Dieting
Encyclopedia
Dieting is the practice of eating
food in a regulated fashion to achieve or maintain a controlled weight. In most cases dieting is used in combination with physical exercise
to lose weight
in those who are overweight
or obese. Some athletes, however, follow a diet to gain weight (usually in the form of muscle
). Diets can also be used to maintain a stable body weight.
Diets to promote weight loss
are generally divided into four categories: low-fat
, low-carbohydrate
, low-calorie
, and very low calorie
. A meta-analysis
of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies. At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized.
The first popular diet was "Banting", named after William Banting
. In his 1863 pamphlet, Letter on Corpulence, Addressed to the Public, he outlined the details of a particular low-carbohydrate, low-calorie diet that had led to his own dramatic weight loss.
(i.e. they restrict carbohydrate intake sufficiently to cause ketosis
).
. The National Institutes of Health reviewed 34 randomized controlled trial
s to determine the effectiveness of low-calorie diets. They found that these diets lowered total body mass by 8% in the short term, over 3–12 months.
and produce an average weekly weight loss of 1.5–2.5 kilograms (3.3–5.5 lb). "2-4-6-8", a popular diet of this variety, follows a four-day cycle in which only 200 calories are consumed the first day, 400 the second day, 600 the third day, 800 the fourth day, and then the cycle repeats. These diets are not recommended for general use as they are associated with adverse side effect
s such as loss of lean muscle mass, increased risks of gout
, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications.
filtering) and celery
and other juicy low-calorie
vegetables (for salt
absorption).
people, or people suffering from obesity
, typically aim to reduce the percentage of body fat
. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person's body shape. To determine the proportion of weight loss that is due to decreased fat tissue, various methods of measuring body fat percentage
have been developed.
Muscle
loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics
) and by maintaining sufficient protein
intake. Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake. According to the National Academy of Sciences
, the Dietary Reference Intake
for protein is 0.8 grams per kilogram of body weight for adults.
Excessive protein intake, though not connected to declined kidney functioning in healthy individuals, may be harmful to those with certain kidney diseases. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous; it has only been shown that these diets are dangerous in individuals already suffering from kidney and liver problems.
The Basal Metabolic Rate
, which is the amount of calories the body expends at rest, meaning without performing any physical activity, is influenced by the person's total weight
and total amount of muscle
. The more muscle, the more calories a person can burn naturally. When the amount of muscle is increased, then more calories can be ingested without gaining weight. Conversely, if the amount of fat
is increased, increasing the number of calories ingested will only add weight.
Normally, when people lose weight, they lose a combination of fat and muscle. If the diet plan includes a daily caloric intake greater than the basal metabolic rate (BMR), the person will most likely lose fat. In contrast, if the person follows a diet that includes a lower caloric intake than the BMR, this person will lose fat but also a higher percentage of muscle. Severe diets may make people lose 50% fat and 50% muscle weight thus affecting their metabolism
because by losing muscle the BMR is affected.
Maintaining muscle mass while losing fat is therefore a key factor to reach both the ideal weight and body
composition. To achieve this goal, experts advise not to reduce carbohydrates aggressively. Fat can be lost by reducing the calorie intake by 20% of daily needs for two days. This reduced calorie intake, even in the presence of 100% carbohydrate consumption, allows for reduction of fat without muscle loss because the glycogen in the muscle is properly replenished.
Exercising on days when the highest amount of carbohydrates is consumed, 1.5 to 2 hours after eating, is also helpful to achieve a balanced fat reduction in the absence of muscle loss. Within this window of time, sugar
and insulin
levels are undergoing a slow decline. When insulin levels start dropping, the pancreas
then produces the hormone glucagon while releasing nutrients stored in the fat cells
to the blood
to be turned into energy
. Conversely, if blood sugar levels suffer a high increase, insulin feeds the muscle cells and deposits excess into fat cells. Furthermore, if insulin levels decrease too much, the muscle cells do not receive the appropriate amount of food they require. There should always be a meal
left during the day after exercising to allow the muscles to recover from exercise.
and the efficiency of utilization. The efficiency of digestion is largely dependent on the type of food being eaten, while efficiency of utilization is affected by a variety of factors, including age, gender, body weight, hormone
levels, and many more.
Chewing
, especially in the elderly, has been shown to increase the intake of micronutrient
s. However, the effect of chewing on the intake of macronutrients, such as sugars, fats, and proteins has not been observed.
provides nutrients from six broad classes: protein
s, fat
s, carbohydrate
s, vitamin
s, dietary mineral
s, and water
. Carbohydrates are metabolized to provide energy. Proteins provide amino acid
s, which are required for cell construction, especially for the construction of muscle cells. Essential fatty acid
s are required for brain and cell membrane construction. Vitamins and trace minerals helps to keep good electrolyte balance and are used for metabolic processes. Dietary fiber
also affects one's health, although it's not digested into the body.
The National Academy of Sciences
and the World Health Organization
publish guidelines for dietary intakes of all known essential nutrients.
Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don't menstruate
) need to be wary of iron poisoning
. Retinol (oil-soluble vitamin A) is toxic in large doses. Vitamin E
supplements have been found in some studies to increase mortality, congenital heart defects in offspring and an increased risk of stroke (see the corresponding article). Most people can obtain their nutritional needs from their diet. In any event, a multivitamin taken once a day will suffice for the majority of the population.
Weight loss diets that manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been shown to be any more effective than diets that maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may, in some cases, lead to malnutrition.
Besides the importance of eating a balanced diet that includes all the necessary nutrients, other factors also contribute to healthy nutrition. As well, drinking sufficient amounts of water can help eliminate toxins and fat. Heavily processed and fried foods as well as sweets, junk foods, and alcohol
should also be avoided in a healthy diet.
Also a topic of great importance discussed among nutritionists as well as psychologists is the attitude to weight-loss and the consumption of food in general. Voicing ideas such as "it's just one burger" during and after weight loss regimes is discouraged, and often is said on the part of an insecure individual who has reached the unfortunate conclusion that nothing can be done any longer and that any effort to do so is futile. The advice given is, avoid reaching such a conclusion, as not only does it change one's perception of the effect of excessive amounts of food on the body, but also encourages a 'lack-lustre' lifestyle and approach to life as a whole.
Nutritionists also agree on the importance of avoiding fats, especially saturated fats, to reduce weight and to be healthier. They also agree on the importance of reducing salt
intake because commercial foods such as snacks, biscuits, and bread
, among others, already contain salt, thus contributing to an excess of salt daily intake.
MyPyramid Food Guidance System is the result of extensive research performed by the United States Department of Agriculture
to revise the original Food Guide Pyramid
. It offers a wide array of personalized options to help individuals make healthy food choices. It also provides advice on physical activity.
(by glycogenolysis
). Glycogen is a complex carbohydrate, 65% of which is stored in skeletal muscles and the remainder, in the liver (totaling about 2,000 kcal in the whole body). It is created from the excess of ingested macronutrients, mainly carbohydrates. When glycogen is nearly depleted, the body begins lipolysis
, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol
and fatty acids, which can be used to generate energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.
Fats are also secreted by the sebaceous gland
s (in the skin).
and Peertrainer
. The latter include, Overeaters Anonymous
, also several groups run by local churches, hospitals, and like-minded individuals.
These organizations' customs and practices differ widely. Some groups are modelled on twelve-step program
s, while others are quite informal. Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking.
showed that dieters who kept a daily food diary (or diet journal), lost twice as much weight as those who did not keep a food log, suggesting that if you write your food down, you wouldn't eat as many calories. Accordingly, diet journal software and websites have gained significant popularity, and help people track calorie consumption, calorie burning, weight loss goals, and nutritional balance.
) of 30 or above, as well as for smoking cessation treatments, Acomplia is still pending FDA approval for use in the United States. Other weight loss medications, like amphetamine
s, are dangerous and are now banned for casual weight loss. Some supplements, including those containing vitamin
s and minerals
, may not be effective for weight loss.
s induce weight loss through the excretion of water. Diuretics, which can be used in the forms of medications, supplements, or herb
s, reduce overall body weight, but have no effect on an individual's total body fat content. Diuretics can thicken the blood, cause cramping, kidney and liver damage. In a single report, the death of Jacqueline Henson was found to be related to swelling in her brain, which was associated with excessive water consumption over a short period of time, while she was on a special water diet.
s such as ephedrine
, green tea
, caffeine
or synephrine
work to increase the basal metabolic rate
.
can be dangerous due to the risk of malnutrition
and should be carried out under medical supervision. During prolonged fasting or very low calorie diet
s, the reduction of blood glucose, the preferred energy source of the brain
, causes the body to deplete its glycogen stores. Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein (including but not limited to skeletal muscle) to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting although some dispute this. The use of short-term fasting, or various forms of intermittent fasting have been used as a form of dieting to circumvent this issue.
) diet versus a low-fat diet (LEARN diet, Ornish diet). The Nurses' Health Study
, an observational cohort study
, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease
. The same study also found no correlation (with multivariate adjustment) between animal fat intake and coronary heart disease (table 4).
A meta-analysis
of randomized controlled trials by the international Cochrane Collaboration
in 2002 concluded that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people. A more recent meta-analysis
that included randomized controlled trials published after the Cochrane review found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."
The Women's Health Initiative
Randomized Controlled Dietary Modification Trial found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily resulted in:
Additional recent randomized controlled trials have found that:
The American Diabetes Association
released for the first time a recommendation (in its January 2008 Clinical Practice Recommendations) for a low carbohydrate diet to reduce weight for those with or at risk of Type 2 diabetes.
(GI) factor is a ranking of foods based on their overall effect on blood sugar levels. The diet based around this research is called the Low GI diet. Low glycemic index foods, such as lentils, provide a slower, more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycemic index foods, such as white bread."
The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".
In a randomized controlled trial
that compared four diets that varied in carbohydrate amount and glycemic index found complicated results:
Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.
A meta-analysis
by the Cochrane Collaboration
concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration
grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.
Eating
Eating is the ingestion of food to provide for all organisms their nutritional needs, particularly for energy and growth. Animals and other heterotrophs must eat in order to survive: carnivores eat other animals, herbivores eat plants, omnivores consume a mixture of both plant and animal matter,...
food in a regulated fashion to achieve or maintain a controlled weight. In most cases dieting is used in combination with physical exercise
Physical exercise
Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, as well as for the purpose of...
to lose weight
Weight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
in those who are overweight
Overweight
Overweight is generally defined as having more body fat than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary...
or obese. Some athletes, however, follow a diet to gain weight (usually in the form of muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
). Diets can also be used to maintain a stable body weight.
Diets to promote weight loss
Weight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
are generally divided into four categories: low-fat
Low-fat diet
According to the USDA, a low-fat diet as the name implies is a diet that consists of little fat, especially saturated fat and cholesterol, which are thought to lead to increased blood cholesterol levels and heart attack...
, low-carbohydrate
Low-carbohydrate diet
Low-carbohydrate diets or low-carb diets are dietary programs that restrict carbohydrate consumption usually for weight control or for the treatment of obesity. Foods high in digestible carbohydrates are limited or replaced with foods containing a higher percentage of proteins and fats...
, low-calorie
Calorie restriction
Caloric restriction , or calorie restriction, is a dietary regimen that restricts calorie intake, where the baseline for the restriction varies, usually being the previous, unrestricted, intake of the subjects...
, and very low calorie
Very Low Calorie Diet
Very low calorie diet is a diet with very or extremely low daily food energy consumption. It is defined as a diet of per day or less. VLCDs are formulated, nutritionally complete, liquid meals containing 800 kilocalories or less per day. VLCDs also contain the recommended daily requirements for...
. A meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies. At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized.
The first popular diet was "Banting", named after William Banting
William Banting
William Banting , was a formerly obese English undertaker who was the first to popularise a weight loss diet based on limiting intake of refined and easily digestible carbohydrates. He undertook his dietary changes at the suggestion of Dr...
. In his 1863 pamphlet, Letter on Corpulence, Addressed to the Public, he outlined the details of a particular low-carbohydrate, low-calorie diet that had led to his own dramatic weight loss.
Low-fat diets
Low-fat diets involve the reduction of the percentage of fat in one's diet. Calorie consumption is reduced because less fat is consumed. Diets of this type include NCEP Step I and II. A meta-analysis of 16 trials of 2–12 months' duration found that low-fat diets (without intentional restriction of caloric intake) resulted in average weight loss of 3.2 kg (7.1 lb) over habitual eating.Low-carbohydrate diets
Low carbohydrate diets such as Atkins and Protein Power are relatively high in protein. Low-carbohydrate diets are sometimes ketogenicKetogenic diet
The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that in medicine is used primarily to treat difficult-to-control epilepsy in children. The diet mimics aspects of starvation by forcing the body to burn fats rather than carbohydrates...
(i.e. they restrict carbohydrate intake sufficiently to cause ketosis
Ketosis
Ketosis is a state of elevated levels of ketone bodies in the body. It is almost always generalized throughout the body, with hyperketonemia, that is, an elevated level of ketone bodies in the blood. Ketone bodies are formed by ketogenesis when the liver glycogen stores are depleted...
).
Low-calorie diets
Low-calorie diets usually produce an energy deficit of 500–1,000 calories per day, which can result in a 0.5 kilogram (1.1 lb) to 1 kilogram (2.2 lb) weight loss per week. Amongst some of the most commonly used low-calorie diets include DASH diet, Diet to Go, and Weight WatchersWeight Watchers
Weight Watchers is an international company that offers various dieting products and services to assist weight loss and maintenance. Founded in 1963 by Brooklyn homemaker Jean Nidetch, it operates in about 30 countries around the world, generally under names that are local translations of “Weight...
. The National Institutes of Health reviewed 34 randomized controlled trial
Randomized controlled trial
A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...
s to determine the effectiveness of low-calorie diets. They found that these diets lowered total body mass by 8% in the short term, over 3–12 months.
Very low-calorie diets
Very low calorie diets provide 200–800 calories per day, maintaining protein intake but limiting calories from both fat and carbohydrates. They subject the body to starvationStarvation
Starvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...
and produce an average weekly weight loss of 1.5–2.5 kilograms (3.3–5.5 lb). "2-4-6-8", a popular diet of this variety, follows a four-day cycle in which only 200 calories are consumed the first day, 400 the second day, 600 the third day, 800 the fourth day, and then the cycle repeats. These diets are not recommended for general use as they are associated with adverse side effect
Adverse effect (medicine)
In medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...
s such as loss of lean muscle mass, increased risks of gout
Gout
Gout is a medical condition usually characterized by recurrent attacks of acute inflammatory arthritis—a red, tender, hot, swollen joint. The metatarsal-phalangeal joint at the base of the big toe is the most commonly affected . However, it may also present as tophi, kidney stones, or urate...
, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications.
Detox diets
Detox diets claim to eliminate undesirable "toxins" from the human body rather than claiming to cause weight loss. Many of these use herbs and other homeopathic remedies, such as dandelion root (for liverLiver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
filtering) and celery
Celery
Apium graveolens is a plant species in the family Apiaceae commonly known as celery or celeriac , depending on whether the petioles or roots are eaten: celery refers to the former and celeriac to the latter. Apium graveolens grows to 1 m tall...
and other juicy low-calorie
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
vegetables (for salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
absorption).
Fat loss versus muscle loss
Weight loss typically involves the loss of fat, water and muscle. OverweightOverweight
Overweight is generally defined as having more body fat than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary...
people, or people suffering from obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
, typically aim to reduce the percentage of body fat
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...
. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person's body shape. To determine the proportion of weight loss that is due to decreased fat tissue, various methods of measuring body fat percentage
Body fat percentage
A person's body mass percentage is the total weight of the person's fat divided by the person's weight and consists of essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than...
have been developed.
Muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics
Calisthenics
Calisthenics are a form of aerobic exercise consisting of a variety of simple, often rhythmical, movements, generally using multiple equipment or apparatus. They are intended to increase body strength and flexibility with movements such as bending, jumping, swinging, twisting or kicking, using...
) and by maintaining sufficient protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
intake. Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake. According to the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
, the Dietary Reference Intake
Dietary Reference Intake
The Dietary Reference Intake is a system of nutrition recommendations from the Institute of Medicine of the U.S. National Academy of Sciences. The DRI system is used by both the United States and Canada and is intended for the general public and health professionals...
for protein is 0.8 grams per kilogram of body weight for adults.
Excessive protein intake, though not connected to declined kidney functioning in healthy individuals, may be harmful to those with certain kidney diseases. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous; it has only been shown that these diets are dangerous in individuals already suffering from kidney and liver problems.
The Basal Metabolic Rate
Basal metabolic rate
Basal Metabolic Rate , and the closely related resting metabolic rate , is the amount of daily energy expended by humans and other animals at rest. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state...
, which is the amount of calories the body expends at rest, meaning without performing any physical activity, is influenced by the person's total weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
and total amount of muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
. The more muscle, the more calories a person can burn naturally. When the amount of muscle is increased, then more calories can be ingested without gaining weight. Conversely, if the amount of fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
is increased, increasing the number of calories ingested will only add weight.
Normally, when people lose weight, they lose a combination of fat and muscle. If the diet plan includes a daily caloric intake greater than the basal metabolic rate (BMR), the person will most likely lose fat. In contrast, if the person follows a diet that includes a lower caloric intake than the BMR, this person will lose fat but also a higher percentage of muscle. Severe diets may make people lose 50% fat and 50% muscle weight thus affecting their metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
because by losing muscle the BMR is affected.
Maintaining muscle mass while losing fat is therefore a key factor to reach both the ideal weight and body
Body
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
composition. To achieve this goal, experts advise not to reduce carbohydrates aggressively. Fat can be lost by reducing the calorie intake by 20% of daily needs for two days. This reduced calorie intake, even in the presence of 100% carbohydrate consumption, allows for reduction of fat without muscle loss because the glycogen in the muscle is properly replenished.
Exercising on days when the highest amount of carbohydrates is consumed, 1.5 to 2 hours after eating, is also helpful to achieve a balanced fat reduction in the absence of muscle loss. Within this window of time, sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
and insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
levels are undergoing a slow decline. When insulin levels start dropping, the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
then produces the hormone glucagon while releasing nutrients stored in the fat cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
to the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
to be turned into energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
. Conversely, if blood sugar levels suffer a high increase, insulin feeds the muscle cells and deposits excess into fat cells. Furthermore, if insulin levels decrease too much, the muscle cells do not receive the appropriate amount of food they require. There should always be a meal
Meal
A meal is an instance of eating, specifically one that takes place at a specific time and includes specific, prepared food.Meals occur primarily at homes, restaurants, and cafeterias, but may occur anywhere. Regular meals occur on a daily basis, typically several times a day...
left during the day after exercising to allow the muscles to recover from exercise.
Energy obtained from food
The energy intake from food is limited by the efficiency of digestionDigestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
and the efficiency of utilization. The efficiency of digestion is largely dependent on the type of food being eaten, while efficiency of utilization is affected by a variety of factors, including age, gender, body weight, hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
levels, and many more.
Chewing
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
, especially in the elderly, has been shown to increase the intake of micronutrient
Micronutrient
Micronutrients are nutrients required by humans and other living things throughout life in small quantities to orchestrate a whole range of physiological functions, but which the organism itself cannot produce. For people, they include dietary trace minerals in amounts generally less than 100...
s. However, the effect of chewing on the intake of macronutrients, such as sugars, fats, and proteins has not been observed.
Proper nutrition
FoodFood
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
provides nutrients from six broad classes: protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s, fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s, carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s, vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s, dietary mineral
Dietary mineral
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. Examples of mineral elements include calcium, magnesium, potassium, sodium, zinc, and iodine...
s, and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. Carbohydrates are metabolized to provide energy. Proteins provide amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s, which are required for cell construction, especially for the construction of muscle cells. Essential fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s are required for brain and cell membrane construction. Vitamins and trace minerals helps to keep good electrolyte balance and are used for metabolic processes. Dietary fiber
Dietary fiber
Dietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...
also affects one's health, although it's not digested into the body.
The National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
and the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
publish guidelines for dietary intakes of all known essential nutrients.
Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don't menstruate
Menstruation
Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...
) need to be wary of iron poisoning
Iron poisoning
Iron poisoning is an iron overload caused by a large excess of iron intake and usually refers to an acute overload rather than a gradual one. The terms has been primarily associated with young children who consumed large quantities of iron supplement pills, which resemble sweets and are widely...
. Retinol (oil-soluble vitamin A) is toxic in large doses. Vitamin E
Vitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...
supplements have been found in some studies to increase mortality, congenital heart defects in offspring and an increased risk of stroke (see the corresponding article). Most people can obtain their nutritional needs from their diet. In any event, a multivitamin taken once a day will suffice for the majority of the population.
Weight loss diets that manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been shown to be any more effective than diets that maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may, in some cases, lead to malnutrition.
Besides the importance of eating a balanced diet that includes all the necessary nutrients, other factors also contribute to healthy nutrition. As well, drinking sufficient amounts of water can help eliminate toxins and fat. Heavily processed and fried foods as well as sweets, junk foods, and alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
should also be avoided in a healthy diet.
Also a topic of great importance discussed among nutritionists as well as psychologists is the attitude to weight-loss and the consumption of food in general. Voicing ideas such as "it's just one burger" during and after weight loss regimes is discouraged, and often is said on the part of an insecure individual who has reached the unfortunate conclusion that nothing can be done any longer and that any effort to do so is futile. The advice given is, avoid reaching such a conclusion, as not only does it change one's perception of the effect of excessive amounts of food on the body, but also encourages a 'lack-lustre' lifestyle and approach to life as a whole.
Nutritionists also agree on the importance of avoiding fats, especially saturated fats, to reduce weight and to be healthier. They also agree on the importance of reducing salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
intake because commercial foods such as snacks, biscuits, and bread
Bread
Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...
, among others, already contain salt, thus contributing to an excess of salt daily intake.
MyPyramid Food Guidance System is the result of extensive research performed by the United States Department of Agriculture
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...
to revise the original Food Guide Pyramid
Food guide pyramid
A food guide pyramid is a triangular or pyramid-shaped nutrition guide divided into sections to show the recommended intake for each food group. The first food pyramid was published in Sweden in 1974. The most widely known food pyramid was introduced by the United States Department of Agriculture...
. It offers a wide array of personalized options to help individuals make healthy food choices. It also provides advice on physical activity.
How the body eliminates fat
All body processes require energy in order to function properly. When the body is expending more energy than it is consuming (e.g. when exercising), the body's cells rely on internally stored energy sources, such as complex carbohydrates and fats, for energy. The first source to which the body turns is glycogenGlycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
(by glycogenolysis
Glycogenolysis
Glycogenolysis is the conversion of glycogen polymers to glucose monomers. Glycogen is catabolized by removal of a glucose monomer through cleavage with inorganic phosphate to produce glucose-1-phosphate...
). Glycogen is a complex carbohydrate, 65% of which is stored in skeletal muscles and the remainder, in the liver (totaling about 2,000 kcal in the whole body). It is created from the excess of ingested macronutrients, mainly carbohydrates. When glycogen is nearly depleted, the body begins lipolysis
Lipolysis
Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
and fatty acids, which can be used to generate energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.
Fats are also secreted by the sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s (in the skin).
Psychological aspects of weight loss
Cognitive Behavior Therapy has been effective in producing long term weight loss.Weight loss groups
Some weight loss groups aim to make money, others work as charities. The former include Weight WatchersWeight Watchers
Weight Watchers is an international company that offers various dieting products and services to assist weight loss and maintenance. Founded in 1963 by Brooklyn homemaker Jean Nidetch, it operates in about 30 countries around the world, generally under names that are local translations of “Weight...
and Peertrainer
PEERtrainer
PEERtrainer is a social networking website that aims to help people lose weight. It is based on the idea that social support is the most important factor in weight loss. Development on the website began in August 2004; it was launched in October 2005. The potential of the company's health oriented...
. The latter include, Overeaters Anonymous
Overeaters Anonymous
Overeaters Anonymous is a twelve-step program for people with problems related to food including, but not limited to, compulsive overeaters, those with binge eating disorder, bulimics and anorexics...
, also several groups run by local churches, hospitals, and like-minded individuals.
These organizations' customs and practices differ widely. Some groups are modelled on twelve-step program
Twelve-step program
A Twelve-Step Program is a set of guiding principles outlining a course of action for recovery from addiction, compulsion, or other behavioral problems...
s, while others are quite informal. Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking.
Food diary
A 2008 study published in the American Journal of Preventive MedicineAmerican Journal of Preventive Medicine
American Journal of Preventive MedicineThe American Journal of Preventive Medicine is the official journal of the American College of Preventive Medicine and the Association for Prevention Teaching and Research. It publishes articles in the areas of prevention research, teaching, practice and policy...
showed that dieters who kept a daily food diary (or diet journal), lost twice as much weight as those who did not keep a food log, suggesting that if you write your food down, you wouldn't eat as many calories. Accordingly, diet journal software and websites have gained significant popularity, and help people track calorie consumption, calorie burning, weight loss goals, and nutritional balance.
Medications
Certain medications can be prescribed to assist in weight loss. The most recent prescription weight loss medication released is Acomplia (generic name Rimonabant), manufactured by Sanofi Aventis. Used to treat obesity in persons with a BMI (body mass indexBody mass index
The body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...
) of 30 or above, as well as for smoking cessation treatments, Acomplia is still pending FDA approval for use in the United States. Other weight loss medications, like amphetamine
Amphetamine
Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
s, are dangerous and are now banned for casual weight loss. Some supplements, including those containing vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s and minerals
Dietary mineral
Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. Examples of mineral elements include calcium, magnesium, potassium, sodium, zinc, and iodine...
, may not be effective for weight loss.
Diuretics
DiureticDiuretic
A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...
s induce weight loss through the excretion of water. Diuretics, which can be used in the forms of medications, supplements, or herb
Herb
Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...
s, reduce overall body weight, but have no effect on an individual's total body fat content. Diuretics can thicken the blood, cause cramping, kidney and liver damage. In a single report, the death of Jacqueline Henson was found to be related to swelling in her brain, which was associated with excessive water consumption over a short period of time, while she was on a special water diet.
Stimulants
StimulantStimulant
Stimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...
s such as ephedrine
Ephedrine
Ephedrine is a sympathomimetic amine commonly used as a stimulant, appetite suppressant, concentration aid, decongestant, and to treat hypotension associated with anaesthesia....
, green tea
Green tea
Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally...
, caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
or synephrine
Synephrine
Synephrine is a drug commonly used for weight loss. While its effectiveness is widely debated, synephrine has gained significant popularity as an alternative to ephedrine, a related substance which has been made illegal or restricted in many countries due to health risks and its use as a precursor...
work to increase the basal metabolic rate
Basal metabolic rate
Basal Metabolic Rate , and the closely related resting metabolic rate , is the amount of daily energy expended by humans and other animals at rest. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state...
.
Dangers of fasting
Lengthy fastingFasting
Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...
can be dangerous due to the risk of malnutrition
Malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
and should be carried out under medical supervision. During prolonged fasting or very low calorie diet
Very Low Calorie Diet
Very low calorie diet is a diet with very or extremely low daily food energy consumption. It is defined as a diet of per day or less. VLCDs are formulated, nutritionally complete, liquid meals containing 800 kilocalories or less per day. VLCDs also contain the recommended daily requirements for...
s, the reduction of blood glucose, the preferred energy source of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
, causes the body to deplete its glycogen stores. Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein (including but not limited to skeletal muscle) to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting although some dispute this. The use of short-term fasting, or various forms of intermittent fasting have been used as a form of dieting to circumvent this issue.
Side effects
Dieting, especially extreme food-intake reduction and rapid weight loss, can have the following side effects and consequences:- Subsequent weight re-gain
- Lowered metabolismMetabolismMetabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, causing future attempts at weight loss to become more difficult, and making weight gain easier - Muscle atrophyMuscle atrophyMuscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass...
- Risk of developing Eating DisorderEating disorderEating disorders refer to a group of conditions defined by abnormal eating habits that may involve either insufficient or excessive food intake to the detriment of an individual's physical and mental health. Bulimia nervosa, anorexia nervosa, and binge eating disorder are the most common specific...
s, especially Anorexia NervosaAnorexia nervosaAnorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...
or Bulimia NervosaBulimia nervosaBulimia nervosa is an eating disorder characterized by binge eating and purging or consuming a large amount of food in a short amount of time, followed by an attempt to rid oneself of the food consumed, usually by purging and/or by laxative, diuretics or excessive exercise. Bulimia nervosa is...
, even if initial intentions of dieting were health-wise - Prolonged hungerHungerHunger is the most commonly used term to describe the social condition of people who frequently experience the physical sensation of desiring food.-Malnutrition, famine, starvation:...
- DepressionDepression (mood)Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...
- Reduced sex driveLibidoLibido refers to a person's sex drive or desire for sexual activity. The desire for sex is an aspect of a person's sexuality, but varies enormously from one person to another, and it also varies depending on circumstances at a particular time. A person who has extremely frequent or a suddenly...
- Fatigue
- IrritabilityIrritabilityIrritability is an excessive response to stimuli. The term is used for both the physiological reaction to stimuli and for the pathological, abnormal or excessive sensitivity to stimuli; It is usually used to refer to anger or frustration....
- Fainting
- SinusParanasal sinusParanasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...
problems (especially post-nasal dripPost-nasal dripPost-nasal drip , also known as Upper Airway Cough Syndrome , occurs when excessive mucus is produced by the nasal mucosa. The excess mucus accumulates in the throat or back of the nose...
) - RashRashA rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...
es - AcidosisAcidosisAcidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....
- Bloodshot eyes
- GallbladderGallbladderIn vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
disease - Seizures
- MalnutritionMalnutritionMalnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
, possibly leading to deathDeathDeath is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury.... - ConstipationConstipationConstipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...
, due to lack of food-intake - DehydrationDehydrationIn physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
, due to lack of fluid-intake
Low carbohydrate versus low fat
Many studies have focused on diets that reduce calories via a low-carbohydrate (Atkins diet, Scarsdale diet, Zone dietZone diet
The Zone diet is a diet popularized in books by biochemist Barry Sears. It advocates consuming calories from carbohydrates, protein, and fat in a balanced ratio.- Theory :...
) diet versus a low-fat diet (LEARN diet, Ornish diet). The Nurses' Health Study
Nurses' Health Study
The Nurses Health Study, established in 1976 by Dr. Frank Speizer, and the Nurses' Health Study II, established in 1989 by Dr. Walter Willett, are the most definitive long-term epidemiological studies conducted to date on older women's health. The study has followed 121,700 female registered...
, an observational cohort study
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
, found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease
Coronary heart disease
Coronary artery disease is the end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium with oxygen and nutrients. It is sometimes also called coronary heart disease...
. The same study also found no correlation (with multivariate adjustment) between animal fat intake and coronary heart disease (table 4).
A meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
of randomized controlled trials by the international Cochrane Collaboration
Cochrane Collaboration
The Cochrane Collaboration is a group of over 28,000 volunteers in more than 100 countries who review the effects of health care interventions tested in biomedical randomized controlled trials. A few more recent reviews have also studied the results of non-randomized, observational studies...
in 2002 concluded that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people. A more recent meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
that included randomized controlled trials published after the Cochrane review found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."
The Women's Health Initiative
Women's Health Initiative
The Women's Health Initiative was initiated by the U.S. National Institutes of Health in 1991. The objective of this women's health research initiative was to conduct medical research into some of the major health problems of older women...
Randomized Controlled Dietary Modification Trial found that a diet of total fat to 20% of energy and increasing consumption of vegetables and fruit to at least 5 servings daily and grains to at least 6 servings daily resulted in:
- no reduction in cardiovascular disease
- no statistically significant reduction in invasive breast cancer
- no reductions in colorectal cancer
Additional recent randomized controlled trials have found that:
- A comparison of Atkins, Zone dietZone dietThe Zone diet is a diet popularized in books by biochemist Barry Sears. It advocates consuming calories from carbohydrates, protein, and fat in a balanced ratio.- Theory :...
, Ornish diet, and LEARN diet in premenopausal women found the greatest benefit from the Atkins diet.
- The choice of diet for a specific person may be influenced by measuring the individual's insulin secretion:
- In young adultsYoung adult (psychology)A young adult, according to Erik Erikson's stages of human development, is generally a person between the age of 20 - 40, whereas an adolescent is a person between the age of 13 - 19, although definitions and opinions vary. The young adult stage in human development precedes middle adulthood. A...
"Reducing glycemic [carbohydrate] load may be especially important to achieve weight loss among individuals with high insulin secretion." This is consistent with prior studies of diabetic patients in which low carbohydrate diets were more beneficial.
The American Diabetes Association
American Diabetes Association
The American Diabetes Association is a United States-based association working to fight the consequences of diabetes, and to help those affected by diabetes...
released for the first time a recommendation (in its January 2008 Clinical Practice Recommendations) for a low carbohydrate diet to reduce weight for those with or at risk of Type 2 diabetes.
Low glycemic index
"The glycemic indexGlycemic index
The glycemic index, glycaemic index, or GI is a measure of the effects of carbohydrates on blood sugar levels. Carbohydrates that break down quickly during digestion and release glucose rapidly into the bloodstream have a high GI; carbohydrates that break down more slowly, releasing glucose more...
(GI) factor is a ranking of foods based on their overall effect on blood sugar levels. The diet based around this research is called the Low GI diet. Low glycemic index foods, such as lentils, provide a slower, more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycemic index foods, such as white bread."
The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount".
In a randomized controlled trial
Randomized controlled trial
A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...
that compared four diets that varied in carbohydrate amount and glycemic index found complicated results:
- Diet 1 and 2 were high carbohydrate (55% of total energy intake)
- Diet 1 was high-glycemic index
- Diet 2 was low-glycemic index
- Diet 3 and 4 were high protein (25% of total energy intake)
- Diet 3 was high-glycemic index
- Diet 4 was low-glycemic index
Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3. Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable.
A meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
by the Cochrane Collaboration
Cochrane Collaboration
The Cochrane Collaboration is a group of over 28,000 volunteers in more than 100 countries who review the effects of health care interventions tested in biomedical randomized controlled trials. A few more recent reviews have also studied the results of non-randomized, observational studies...
concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles. However, the Cochrane Collaboration
Cochrane Collaboration
The Cochrane Collaboration is a group of over 28,000 volunteers in more than 100 countries who review the effects of health care interventions tested in biomedical randomized controlled trials. A few more recent reviews have also studied the results of non-randomized, observational studies...
grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index.
See also
- Body imageBody imageBody image refers to a person's perception of the aesthetics and sexual attractiveness of their own body. The phrase body image was first coined by the Austrian neurologist and psychoanalyst Paul Schilder in his masterpiece The Image and Appearance of the Human Body...
- Eating disorderEating disorderEating disorders refer to a group of conditions defined by abnormal eating habits that may involve either insufficient or excessive food intake to the detriment of an individual's physical and mental health. Bulimia nervosa, anorexia nervosa, and binge eating disorder are the most common specific...
- Carbon footprintCarbon footprintA carbon footprint has historically been defined as "the total set of greenhouse gas emissions caused by an organization, event, product or person.". However, calculating a carbon footprint which conforms to this definition is often impracticable due to the large amount of data required, which is...
- Crash dietCrash dietA crash diet is a diet which is extreme in its nutritional deprivations, typically severely restricting calorie intake. It is meant to achieve rapid weight loss and may differ from outright starvation only slightly. It is not meant to last for long periods of time, at most a few weeks. ...
- DietitianDietitianDietitians supervise the preparation and service of food, develop modified diets, participate in research, and educate individuals and groups on good nutritional habits. The goals of dietitians are to provide medical nutritional intervention, and to obtain, safely prepare, serve and advise on...
- FastingFastingFasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...
- Food Balance WheelFood Balance WheelThe Food Balance Wheel suggests an alternate interpretation of the USDA Food Guide Pyramid recommendations for balanced eating. Created by author Art Dragon, it converts the principles of the food pyramid from a number-based format to a visual presentation that may be more accessible to users...
- Food faddismFood faddismThe phrases food faddism and fad diet originally referred to idiosyncratic diets and eating patterns that promote short-term weight loss, usually with no concern for long-term weight maintenance, and enjoy temporary popularity...
- Healthy dietHealthy dietA healthy diet is one that helps maintain or improve general health. It is important for lowering many chronic health risks, such as obesity, heart disease, diabetes, hypertension and cancer. A healthy diet involves consuming appropriate amounts of all essential nutrients and an adequate amount of...
- Intermittent fastingIntermittent fastingIntermittent fasting is a pattern of eating that alternates between periods of fasting and non-fasting. A specific form of IF is alternate day fasting , which is a 48-hour routine typically composed of a 24-hour fast followed by a 24-hour non-fasting period...
- List of diets
- National Weight Control RegistryNational Weight Control RegistryThe National Weight Control Registry is a research study that includes people who have lost at least 13.6 kg of weight and kept it off for at least one year. There are currently over 10,000 members enrolled in the study, making it perhaps the largest study of weight loss ever conducted...
- NutrigenomicsNutrigenomicsNutrigenomics is the study of the effects of foods and food constituents on gene expression. It is about how our DNA is transcribed into mRNA and then to proteins and provides a basis for understanding the biological activity of food components...
- Nutritional rating systemsNutritional rating systemsNutritional rating systems are methods of ranking or rating food products or food categories to communicate the nutritional value of food in a simplified manner to a target audience...
- Nutrition scaleNutrition scaleA Nutrition scale is a weighing instrument that output precise nutritional information for foods or liquids. Most scales calculate calories, carbohydrates, and fats, with more sophisticated scales calculating additional nutrients such as Vitamin K, potassium, magnesium, and sodium.Scales often use...
- High residue dietHigh residue diet- General guidelines :Women should aim for at least 21 to 25 grams of fiber daily. Men should try for 30 to 38 grams daily.- Foods to include :High fiber foods include whole grain breads and cereals, vegetables and fruits .- External links :* livestrong.com...
- UnderweightUnderweightThe term underweight refers to a human who is considered to be under a healthy weight. "Underweight" means weighing less than what is expected to be a healthy person . The definition is usually made with reference to the body mass index . A BMI of under 18.5 is usually referred to as underweight...
- Online weight loss plansOnline weight loss plansOnline weight loss plans are web-based fitness programs designed to help participants lose weight. They usually include assistance in the areas necessary for weight loss. For example, weight loss information, goal setting, progress tracking, meal and workout planning, and personal support from...
External links
- The food pyramid: Video lectures at the Harvard School of public health
- US News and World Report, Health: Eat Like Our Ancestors. An Interview with Harvard Psychology’s Deirdre Barrett 6/29/07
- A PBS Frontline interview with Prof. Walter Willett, Chair of Harvard's nutrition department
- "Not All Calories Are Created Equal, Author Says". Excerpt from Good Calories, Bad Calories and NPR interview with Gary TaubesGary TaubesGary Taubes is an American science writer.He is the author of Nobel Dreams , Bad Science: The Short Life and Weird Times of Cold Fusion , and Good Calories, Bad Calories , titled The Diet Delusion in the UK and Australia. His book Why We Get Fat: And What to Do About It was released in December...
and Dr. Ronald KraussRonald KraussRonald M. Krauss is Director of Atherosclerosis Research at Children's Hospital Oakland Research Institute, Adjunct Professor of Medicine, UCSF, Adjunct Professor of Nutritional Sciences, University of California at Berkeley, and Guest Senior Scientist in the Genome Sciences Division of Lawrence...
(November 2, 2007).