Low-carbohydrate diet

Low-carbohydrate diet

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Low-carbohydrate diets or low-carb diets are dietary programs that restrict 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...

 consumption usually for weight control or for the treatment of 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...

. Foods high in digestible carbohydrates (e.g. 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...

, pasta
Pasta
Pasta is a staple food of traditional Italian cuisine, now of worldwide renown. It takes the form of unleavened dough, made in Italy, mostly of durum wheat , water and sometimes eggs. Pasta comes in a variety of different shapes that serve for both decoration and to act as a carrier for the...

) are limited or replaced with foods containing a higher percentage of proteins and 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 (e.g. meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

, poultry, fish, shellfish, eggs, cheese, nuts, seeds and peanuts) and other foods low in carbohydrates (e.g. most salad vegetables), although other vegetable
Vegetable
The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....

s and fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

s (especially berries
Berry
The botanical definition of a berry is a fleshy fruit produced from a single ovary. Grapes are an example. The berry is the most common type of fleshy fruit in which the entire ovary wall ripens into an edible pericarp. They may have one or more carpels with a thin covering and fleshy interiors....

) are often allowed. The amount of carbohydrate allowed varies with different low-carbohydrate diets.

Such diets are sometimes ketogenic (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...

), such as the Induction phase of the Atkins diet
Atkins Nutritional Approach
The Atkins diet, officially called the Atkins Nutritional Approach, is a low-carbohydrate diet created by Robert Atkins from a research paper he read in the Journal of the American Medical Association published by Gordon Azar and Walter Lyons Bloom. Atkins stated that he used the study to resolve...

. Some sources, though, consider less restrictive variants to be low-carbohydrate as well.

In addition to obesity, low-carbohydrate diets are used as treatments for some other conditions, notably diabetes, epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

,, chronic fatigue syndrome
Chronic fatigue syndrome
Chronic fatigue syndrome is the most common name used to designate a significantly debilitating medical disorder or group of disorders generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months, not due to ongoing exertion, not substantially...

 (see 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...

) and polycystic ovarian syndrome.

Prehistory



As with the Paleolithic diet
Paleolithic diet
The modern dietary regimen known as the Paleolithic diet , also popularly referred to as the caveman diet, Stone Age diet and hunter-gatherer diet, is a nutritional plan based on the presumed ancient diet of wild plants and animals that various hominid species habitually consumed during the...

, several advocates of low-carbohydrate diets have argued that they are closer to the ancestral diet of humans before the invention of agriculture, and therefore that humans are genetically adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....

 to diets low in carbohydrate. Direct archaeological or fossil evidence on nutrition during the Paleolithic
Paleolithic
The Paleolithic Age, Era or Period, is a prehistoric period of human history distinguished by the development of the most primitive stone tools discovered , and covers roughly 99% of human technological prehistory...

 era, when all humans subsisted by hunting and gathering
Hunting and gathering
Hunting and gathering may refer to:*Hunting and gathering, the subsistence method based on edible plants and animals from the wild*Hunting and Gathering...

, is limited, but suggests that humans evolved from the vegetarian diets common to other great apes
Hominidae
The Hominidae or include them .), as the term is used here, form a taxonomic family, including four extant genera: chimpanzees , gorillas , humans , and orangutans ....

 to one with a greater level of meat eating. Some close relatives of modern Homo sapiens, such as the Neanderthal
Neanderthal
The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...

s, appear to have been almost exclusively carnivorous. A more detailed picture of early human diets before the invention of agriculture may be obtained by analogy to contemporary hunter-gatherers. According to one survey of these societies, a relatively low carbohydrate (22–40% of total energy), animal food-centered diet is preferred "whenever and wherever it [is] ecologically possible", and where plant foods do predominate carbohydrate consumption remains low because wild plants are much lower in carbohydrate and higher in fiber than modern domesticated crops. Primatologist Katherine Milton, however, has argued that the survey data this conclusion is based on inflates the animal content of typical hunter-gatherer diets; much of it was based on early ethnography
Ethnography
Ethnography is a qualitative method aimed to learn and understand cultural phenomena which reflect the knowledge and system of meanings guiding the life of a cultural group...

 which may have overlooked the role of women in gathering plant foods. She has also highlighted the diversity of both ancestral and contemporary foraging diets, arguing that there is no evidence that humans are especially adapted to a single Paleolithic diet over and above the vegetarian diets characteristic of the last thirty million years of primate evolution.

The invention of agriculture brought about a rise in carbohydrate levels in human diets. The industrial age
Industrial Age
Industrial Age may refer to:*Industrialisation*The Industrial Revolution...

 has seen a particularly steep rise in refined carbohydrate levels in Western
Western world
The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

 societies.

Early dietary science


In 1797 Dr. John Rollo reported on the results of treating two diabetic Army officers with a low-carbohydrate diet and medications. A very low-carbohydrate, ketogenic diet was the standard treatment for diabetes throughout the 19th century.

In 1863 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...

, an obese English undertaker and coffin maker, published "Letter on Corpulence Addressed to the Public" in which he described a diet for weight control giving up bread, butter, milk, sugar, beer and potatoes. His booklet was widely read, so much so that some people used the term "Banting" for the activity usually called "dieting."

In 1888, James Salisbury
James Salisbury
James Henry Salisbury, M.D. was a 19th-century American physician, and the inventor of the Salisbury steak....

 introduced the Salisbury steak
Salisbury steak
Salisbury steak is a dish made from a blend of minced beef and other ingredients, which is shaped to resemble a steak, and usually is served with gravy / brown sauce. Hamburger steak is a similar product, but differs in ingredients....

 as part of his high-meat diet, which limited vegetables, fruit, starches, and fats to one-third of the diet.

In 1967, Dr. Irwin Stillman published The Doctor's Quick Weight Loss Diet
Stillman diet
The Doctor's Quick Weight Loss Diet was created by Irwin Maxwell Stillman, M.D. in 1967. It's an early form of the high-protein and low-carbohydrate diets. It differs from low-carbohydrate diets such as the Atkins Plan in that it is also a low-fat diet.The diet includes lean beef, veal, chicken,...

. The "Stillman Diet" is a high-protein, low-carbohydrate and low-fat diet
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...

. It is regarded as one of the first low-carbohydrate diets to become popular in the US. Other low-carbohydrate diets in the 1960s included the Air Force Diet and the Drinking Man’s Diet. Austrian physician Dr Wolfgang Lutz published his book Leben Ohne Brot (Life Without Bread) in 1967. However, it was hardly noticed in the English-speaking world.

In 1972, Dr. Robert Atkins
Robert Atkins (nutritionist)
Robert Coleman Atkins, MD was an American physician and cardiologist, best known for the Atkins Nutritional Approach , a popular but controversial way of dieting that entails close control of carbohydrate consumption, emphasizing protein and fat intake, including saturated fat in addition to...

 published Dr. Atkins Diet Revolution which advocated a low-carbohydrate diet he had successfully used in treating patients in the 1960s (having himself developed the diet from an unspecified article published in JAMA
Journal of the American Medical Association
The Journal of the American Medical Association is a weekly, peer-reviewed, medical journal, published by the American Medical Association. Beginning in July 2011, the editor in chief will be Howard C. Bauchner, vice chairman of pediatrics at Boston University’s School of Medicine, replacing ...

). The book met with some success but, because of research at that time suggesting risk factors associated with excess fat and protein, it was widely criticized by the mainstream medical community as being dangerous and misleading, thereby limiting its appeal at the time. Among other things critics pointed out that Dr. Atkins had done little real research into his theories and based them mostly on anecdotal evidence. Later that decade, Walter Voegtlin and Dr. Herman Tarnower published books advocating the Stone age diet and Scarsdale diet, respectively, each meeting with moderate success.

The concept of the glycemic index
Glycemic 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...

 was developed about 1981 by Dr. David Jenkins to account for variances in speed of digestion of carbohydrates (e.g., the sugar in cooked carrots has more rapid effect than pure glucose). This concept classifies foods according to the rapidity of their effect on blood sugar levels with fast digesting simple carbohydrates causing a sharper increase and slower digesting complex carbohydrates such as whole grains a slower one. The concept has been extended to include amount of carbohydrate actually absorbed as well, as a tablespoonful of cooked carrots is less significant overall than a large baked potato (effectively pure starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

, which is efficiently absorbed as glucose), despite differences in glycemic index.

Low-carb diets since the 1990s


In the 1990s Dr. Atkins published Dr. Atkins New Diet Revolution and other doctors began to publish books based on the same principles. This has been said to be the beginning of the "low carb craze." During the late 1990s and early 2000s low-carbohydrate diets became some of the most popular diets in the U.S. (by some accounts as much as 18% of the population was using a low-carbohydrate diet at its peak) and spread to many countries. These were noted by some food manufacturers and restaurant chains as substantially affecting their businesses (notably Krispy Kreme
Krispy Kreme
Krispy Kreme is the name of an international chain of doughnut stores that was founded by Vernon Rudolph in 1937 in Winston-Salem, North Carolina. The parent company of Krispy Kreme is Krispy Kreme Doughnuts, Inc...

). Some in the mainstream medical community continued to denounce low-carbohydrate diets as being a dangerous trend. It is, however, valuable to note that many of these same doctors and institutions at the same time quietly began altering their own advice to be closer to the low-carbohydrate recommendations (e.g. eating more protein, eating more fiber/less starch, reducing consumption of juices by children). The low-carbohydrate advocates did some adjustments of their own, increasingly advocating controlling fat and eliminating trans fat
Trans fat
Trans fat is the common name for unsaturated fat with trans-isomer fatty acid. Because the term refers to the configuration of a double carbon-carbon bond, trans fats are sometimes monounsaturated or polyunsaturated, but never saturated....

. Many of the diet guides and gurus that appeared at this time intentionally distanced themselves from Atkins and the term low carb (because of the controversies) even though their recommendations were based on largely the same principles (e.g. the Zone diet
Zone 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 :...

). As a result, it is often a matter of debate which diets are really low-carbohydrate and which are not. The 1990s and 2000s also saw the publication of an increased number of clinical studies regarding the effectiveness and safety (pro and con) of low-carbohydrate diets (see low-carbohydrate diet medical research
Medical research related to low-carbohydrate diets
Low-carbohydrate diets became a major weight loss and health maintenance trend during the late 1990s and early 2000s. While their popularity has waned recently from its peak, they remain popular. This diet trend has stirred major controversies in the medical and nutritional sciences communities...

).

After 2004 the popularity of this diet trend began to wane significantly although it still remains quite popular. In spite of the decline in popularity this diet trend has continued to quietly garner attention in the medical and nutritional science communities.

Practices and theories


The term "low-carbohydrate diet" today is most strongly associated with the Atkins Diet. However, there is an array of other diets that share to varying degrees the same principles (e.g. the Zone Diet
Zone 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 :...

, the Protein Power Lifeplan, The Primal Blueprint, the Go Lower Diet, The Earth Diet
The Earth Diet
The Earth Diet is a lifestyle designed by actress and former beauty queen Liana Werner-Gray. Although the original purpose of the lifestyle is to focus on the abundance of what the earth provides naturally, word of the diet spread and quickly gained popularity as a means to lose weight and reduce...

 and the South Beach Diet
South Beach Diet
The South Beach Diet is a diet plan designed by cardiologist Arthur Agatston and dietician Marie Almon as an alternative to low-fat approaches such as the Ornish Diet and the Pritikin Diet advocated by the American Heart Association in the 1980s. Although the original purpose of the diet was to...

). The American Academy of Family Physicians
American Academy of Family Physicians
The American Academy of Family Physicians was founded in 1947 to promote the science and art of family medicine. It is one of the largest medical organizations in the United States, with over 100,000 members...

 defines low-carbohydrate diets as diets that restrict carbohydrate intake to 20g to 60g per day. Atkins (in the later phases) and some other low-carbohydrate diets exceed the 60g limit definition by this group. There is no widely accepted definition of what precisely constitutes a low-carbohydrate diet. It is important to note that the level of carbohydrate consumption defined as low-carbohydrate by medical researchers may be different from the level of carbohydrate defined by diet advisors. For the purposes of this discussion, this article focuses on diets that reduce (nutritive) 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...

 intake sufficiently to dramatically reduce 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....

 production in the body and to encourage 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...

 (production of ketones to be used as energy in place of glucose).

Although originally low-carbohydrate diets were created based on anecdotal evidence of their effectiveness, today there is a much greater theoretical basis on which these diets rest. The key scientific principle which forms the basis for these diets is the relationship between consumption of carbohydrates and the subsequent effect on blood sugar
Blood sugar
The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...

 (i.e. blood glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

) and on production of certain specific 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...

s. Blood sugar levels in the human body must be maintained in a fairly narrow range to maintain health. The two primary hormones related to regulating blood sugar levels, produced in 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...

, are insulin, which lowers blood sugar levels (among many other effects, most of considerable metabolic significance), and glucagon
Glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...

, which raises blood sugar levels. In general, most western
Western world
The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

 diets (and many others) are sufficiently high in nutritive carbohydrates that nearly all meals evoke insulin secretion from the beta cells in the pancreas; carbohydrates which are digested to produce glucose in the blood stream are the primary control for insulin secretion. Another aspect of insulin secretion is control of 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...

; in the non-ketotic state, the human body stores dietary fat in fat cells (i.e., adipose tissue) and preferentially uses glucose as cellular fuel. By contrast, low-carbohydrate diets, or more properly, diets that are very low in nutritive carbohydrates, evoke less insulin (to cover the ingested glucose in the blood stream), leading to longer and more frequent episodes of ketosis. Some researchers suggest that this causes body fat to be eliminated from the body, although this theory remains controversial, insofar as it refers to excretion of lipids (i.e., fat and oil) and not to fat metabolism during ketosis.

Low-carbohydrate diet advocates in general recommend reducing nutritive carbohydrates (commonly referred to as "net carbs," i.e. grams of total carbohydrates reduced by the non-nutritive carbohydrates) to very low levels. This means sharply reducing consumption of desserts, breads, pastas, potatoes, rice, and other sweet or starchy foods. Some recommend levels less than 20 grams of "net carbs" per day, at least in the early stages of dieting (for comparison, a single slice of white bread typically contains 15 grams of carbohydrate, almost entirely starch). By contrast, the U.S. Institute of Medicine
Institute of Medicine
The Institute of Medicine is a not-for-profit, non-governmental American organization founded in 1970, under the congressional charter of the National Academy of Sciences...

 recommends a minimum intake of 130 grams of carbohydrate per day (the FAO
Food and Agriculture Organization
The Food and Agriculture Organization of the United Nations is a specialised agency of the United Nations that leads international efforts to defeat hunger. Serving both developed and developing countries, FAO acts as a neutral forum where all nations meet as equals to negotiate agreements and...

 and WHO
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...

 similarly recommend that the majority of dietary energy come from carbohydrates).

Low-carbohydrate diets often differ in the specific amount of carbohydrate intake allowed, whether certain types of foods are preferred, whether occasional exceptions are allowed, etc. Generally they all agree that processed sugar should be eliminated, or at the very least greatly reduced, and similarly generally discourage heavily processed grains (white bread, etc.). Low-carbohydrate diets vary greatly in their recommendations as to the amount of fat allowed in the diet. The Atkins Diet does not limit fat. Others recommend a moderate fat intake.

Although low-carbohydrate diets are most commonly discussed as a weight-loss approach, some experts have proposed using low-carbohydrate diets to mitigate or prevent diseases including diabetes, metabolic disease and epilepsy. Some low-carbohydrate proponents and others agrue that the rise in carbohydrate consumption, especially refined carbohydrates, caused the epidemic levels of many diseases in modern society, including metabolic disease and type 2 diabetes.

There is also a category of diets known as low-glycemic-index diets
Glycemic 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...

 (low-GI diets) or low-glycemic-load diets (low-GL diets), in particular the Low GI Diet by Brand-Miller et al. In reality, low-carbohydrate diets can also be low-GL diets (and vice versa) depending on the carbohydrates in a particular diet. In practice, though, "low-GI"/"low-GL" diets differ from "low-carb" diets in the following ways. First, low-carbohydrate diets treat all nutritive carbohydrates as having the same effect on metabolism, and generally assume that their effect is predictable. Low-GI/low-GL diets are based on the measured change in blood glucose levels in various carbohydrates - these vary markedly in laboratory studies. The differences are due to poorly understood digestive differences between foods. However, as foods influence digestion in complex ways (e.g., both protein and fat delay absorption of glucose from carbohydrates eaten at the same time) it is difficult to even approximate the glycemic effect (e.g., over time or even in total in some cases) of a particular meal.

Another related diet type, the low-insulin-index diet
Insulin index
The Insulin Index is a measure used to quantify the typical insulin response to various foods. The index is similar to the Glycemic Index and Glycemic Load, but rather than relying on blood glucose levels, the Insulin Index is based upon blood insulin levels...

, is similar except that it is based on measurements of direct insulemic responses (i.e., the amount of 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....

 in the bloodstream) to food rather than glycemic response (the amount of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 in the bloodstream). Although such diet recommendations mostly involve lowering nutritive carbohydrates, there are some low-carbohydrate foods that are discouraged as well (e.g., beef). Insulin secretion is stimulated (though less strongly) by other dietary intake. Like glycemic index diets, there is difficulty predicting the insulin secretion from any particular meal, due to assorted digestive interactions and so differing effects on insulin release.

Ketosis and insulin synthesis: what is normal?


At the heart of the debate about most low carbohydrate diets are fundamental questions about what is a normal diet and how the human body is supposed to operate. These questions can be outlined as follows:

The diets of most people in modern western
Western world
The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

 nations, especially the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, contain large amounts of starches and often substantial amounts of sugars, including fructose
Fructose
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...

. Most westerners seldom exhaust stored glycogen supplies and hence rarely go into ketosis. This has been regarded by medical science in the last century as normal for humans. Ketosis had widely been regarded as harmful and potentially life-threatening, unnecessarily stressing the liver and causing destruction of muscle tissues, and ketosis had sometimes been confused with ketoacidosis
Ketoacidosis
Ketoacidosis is a metabolic state associated with high concentrations of ketone bodies, formed by the breakdown of fatty acids and the deamination of amino acids. The two common ketones produced in humans are acetoacetic acid and β-hydroxybutyrate....

, a dangerous and extreme ketotic condition associated with diabetes. A perception developed that getting energy chiefly from dietary protein rather than carbohydrates causes liver damage and that getting energy chiefly from dietary fats rather than carbohydrates causes 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...

 and other health problems. This view is still held by the majority of those in the medical and nutritional science communities. However, it is now widely recognized that periodic ketosis is in fact normal, and that ketosis provides a number of surprising benefits, including neuroprotection against diverse types of cellular injury.

People who eschew low carbohydrate diets cite hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...

 and ketoacidosis as a risk factor, but these are only problematic for people such as diabetics, who have impaired regulation of gluconeogenesis and ketone metabolism.

A diet very low in starches and sugars induces several adaptive responses. Low blood glucose causes the pancreas to produce glucagon
Glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...

, which stimulates the liver to convert stored glycogen into glucose and release it into the blood. When liver glycogen stores are exhausted, the body starts utilizing fatty acids instead of glucose. The brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 cannot use fatty acids for energy, and instead uses ketones produced from fatty acids by the liver. By using fatty acids and ketones as energy sources, supplemented by conversion of proteins to glucose (gluconeogenesis
Gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....

), the body can maintain normal levels of blood glucose without dietary carbohydrates.

Most advocates of low-carbohydrate diets, such as the Atkins Diet, argue that the human body is adapted to function primarily in ketosis. They argue that high insulin levels can cause many health problems, most significantly fat storage and weight gain. They argue that the purported dangers of ketosis are unsubstantiated (some of the arguments against ketosis result from confusion between ketosis and ketoacidosis
Ketoacidosis
Ketoacidosis is a metabolic state associated with high concentrations of ketone bodies, formed by the breakdown of fatty acids and the deamination of amino acids. The two common ketones produced in humans are acetoacetic acid and β-hydroxybutyrate....

 which is a mostly diabetic condition unrelated to dieting or low-carbohydrate intake). They also argue that fat in the diet only contributes to heart disease in the presence of high insulin levels and that if the diet is instead adjusted to induce ketosis, fat and cholesterol in the diet are not a major concern (although most do not advocate unrestricted fat intake and do advocate avoiding trans fat
Trans fat
Trans fat is the common name for unsaturated fat with trans-isomer fatty acid. Because the term refers to the configuration of a double carbon-carbon bond, trans fats are sometimes monounsaturated or polyunsaturated, but never saturated....

).

On a high-carbohydrate diet, glucose is used by cells in the body for the energy needed for their basic functions, and about 2/3 of body cells require insulin in order to use glucose. Excessive amounts of blood glucose are thought to be a primary cause of the complications of diabetes; when glucose reacts with body proteins (resulting in glycosolated proteins) and change their behavior. Perhaps for this reason, the amount of glucose tightly maintained in the blood is quite low. Unless a meal is very low in starches and sugars, blood glucose will rise for a period of an hour or two after a meal. When this occurs, beta cells in 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...

 release insulin to cause uptake of glucose into cells. In liver and muscle cells, more glucose is taken in than is needed and stored as glycogen
Glycogen
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...

 (once called 'animal starch'). Diets with a high starch/sugar content, therefore, cause release of more insulin and so more cell absorption. In diabetics, glucose levels vary in time with meals and vary a little more as a result of high carbohydrate content meals. In non-diabetics, blood sugar levels are restored to normal levels within an hour or two, regardless of the content of a meal.

While there are Essential fatty acids (EFA) and Essential amino acids (EAA) and while a diet devoid of EFA or EAA will result in eventual death, a diet completely without carbohydrates can be maintained indefinitely because fatty acids include a carbohydrate backbone (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...

). There are essential fatty acids and amino acids for structural building blocks, not energy. EPA and EAA will be converted into intermediates for the carbohydrate metabolism, even if it depletes their essential stocks. However, a very low carbohydrate diet (less than 20g per day) may negatively affect certain biomarkers and produce detrimental effects in certain types of individuals (for instance, those with kidney problems). The opposite is also true - for instance, clinical experience suggests very low carbohydrate diet for patients with metabolic syndrome
Metabolic syndrome
Metabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...

.

Studies on health effects


Because of the substantial controversy regarding low-carbohydrate diets and even disagreements in interpreting the results of specific studies, it is difficult to objectively summarize the research in a way that reflects scientific consensus. Although there has been some research done throughout the twentieth century, most directly relevant scientific studies have occurred in the 1990s and early 2000s and, as such, are relatively new. Researchers and other experts have published articles and studies that run the gamut from promoting the safety and efficacy of these diets to questioning their long-term validity to outright condemning them as dangerous. Until recently a significant criticism of the diet trend was that there were no studies that evaluated the effects of the diets beyond a few months. However, studies are emerging which evaluate these diets over much longer periods, controlled studies as long as two years and survey studies as long as two decades.

Weight loss


A 2003 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 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." A 2007 JAMA study comparing the effectiveness of the Atkins low-carb diet to several other popular diets concluded "In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets."

A July 2009 study of existing dietary habits associated a low carbohydrate diet with obesity, although the study drew no explicit conclusion regarding the cause: Whether the diet resulted in the obesity or the obesity motivated people to adopt the diet.

One theory is that one of the reasons people lose weight on low carbohydrate diet is related to phenomenon of spontaneous reduction in food intake.

Blood lipids


Potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol and total cholesterol values when low-carbohydrate diets to induce weight loss are considered. A 2008 systematic review
Systematic review
A systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine...

 of randomized controlled studies that compared low-carbohydrate diets to low-fat/low-calorie diets and found that measurements of weight, HDL cholesterol, triglyceride
Triglyceride
A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....

 levels and systolic blood pressure were significantly better in groups that followed low-carbohydrate diets. The authors of this review also found a higher rate of attrition in groups with low-fat diets, and concluded that "evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year," but they also called for more long-term studies.

Mortality


A study of more than 100,000 people over more than 20 years within 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...

 came to the result that a low-carbohydrate diet high in vegetables, with a large proportion of proteins and oils coming from plant sources, decreases mortality with a hazard ratio
Hazard ratio
In survival analysis, the hazard ratio is the ratio of the hazard rates corresponding to the conditions described by two sets of explanatory variables. For example, in a drug study, the treated population may die at twice the rate per unit time as the control population. The hazard ratio would be...

 of 0.8. In contrast, a low-carbohydrate diet with largely animal sources of protein and fat increases mortality, with a hazard ratio of 1.1.
This study, however, has been met with criticism, due to the unreliability of the self-administered food frequency questionnaire, as compared to food journaling, as well as classifying "low-carbohydrate" diets based on comparisons to the group as a whole (decile method) rather than surveying dieters following established low-carb dietary guidelines like the Atkins or Paleo diet.

Opinions from major governmental and medical organizations


Although opinions regarding low-carbohydrate diets vary greatly throughout the medical and nutritional science communities, major government bodies as well as major medical and nutritional associations have generally opposed this nutritional regimen. In recent years, however, some of these same organizations have gradually begun to relax their opposition to the point that some have even voiced cautious support for low-carbohydrate diets. The following are official statements from some of these organizations.
American Academy of Family Physicians
The AAFP
American Academy of Family Physicians
The American Academy of Family Physicians was founded in 1947 to promote the science and art of family medicine. It is one of the largest medical organizations in the United States, with over 100,000 members...

 released a discussion paper on the Atkins Diet specifically in 2006. Although the paper expresses reservations about the Atkins plan they acknowledge it as a legitimate weight loss approach.
American Diabetes Association
The ADA
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...

 revised their Nutrition Recommendations and Interventions for Diabetes in 2008 to acknowledge low-carbohydrate diets as a legitimate weight-loss plan.
The recommendations fall short of endorsing low-carbohydrate diets as a long-term health plan nor do they give any preference to these diets. Nevertheless, this is perhaps the first statement of support—albeit for the short-term—by one of the foremost medical organizations. In its 2009 publication of Clinical Practice Recommendations, The ADA again reaffirmed its acceptance of carbohydrate-controlled diets as an effective treatment for short-term (up to one year) weight loss among obese people suffering from type two diabetes.
American Dietetic Association
As of 2003 in commenting on a study in the Journal of the American Medical Association, a spokesperson for the American Dietetic Association
American Dietetic Association
The American Dietetic Association is the United States' largest organization of food and nutrition professionals, with nearly 72,000 members. The American Dietetic Association is officially changing its name to the Academy of Nutrition and Dietetics. The announcement was made Saturday, September...

 reiterated the association's belief that "there is no magic bullet to safe and healthful weight loss." The Association specifically endorses the high-carbohydrate diet recommended by 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...

.
American Heart Association
The official statement from the AHA
American Heart Association
The American Heart Association is a non-profit organization in the United States that fosters appropriate cardiac care in an effort to reduce disability and deaths caused by cardiovascular disease and stroke. It is headquartered in Dallas, Texas...

 regarding these diets states categorically that the association "doesn't recommend high-protein diets."
A science advisory from the association further states the associations belief that these diets are "associated with increased risk for coronary heart disease." The AHA has been one of the most adamant opponents of low-carbohydrate diets. Dr. Robert Eckel, past president, noted that the association supported low-fat and low-saturated-fat diets, but that a low-carbohydrate diet could potentially meet AHA guidelines.

Australian Heart Foundation
The position statement by the Heart Foundation regarding low-carbohydrate diets states that "the Heart Foundation does not support the adoption of VLCARB diets for weight loss."
Although the statement recommends against use of low-carbohydrate diets it explains that their major concern is saturated fats as opposed to carbohydrate restriction and protein. Moreover, other statements suggest that their position might be re-evaluated in the event of more evidence from longer-term studies.
Food Standards Agency (UK)
The consumer advice statements of the FSA
Food Standards Agency
The Food Standards Agency is a non-ministerial government department of the Government of the United Kingdom. It is responsible for protecting public health in relation to food throughout the United Kingdom and is led by a board appointed to act in the public interest...

 regarding low-carbohydrate diets state that "rather than avoiding starchy foods, it's better to try and base your meals on them."
They further state concerns regarding fat consumption in low-carbohydrate diets.
Heart & Stroke Foundation (Canada)
The official position statement of the Heart & Stroke Foundation
Heart and Stroke Foundation of Canada
The Heart and Stroke Foundation of Canada is a registered Canadian charity. The foundation's purpose is centered around educating individuals about the prevention and management of heart disease and stroke, and to fund medical research regarding the causes of these conditions...

 states "Do not follow a low carbohydrate diet for purposes of weight loss." They state concerns regarding numerous health risks particularly those related to high consumption of "saturated and trans fats".
National Board of Health and Welfare (Sweden)
In 2008, the Socialstyrelsen
Swedish National Board of Health and Welfare
The Swedish National Board of Health and Welfare is a Swedish government agency. The agency was the result of a merge between the Swedish Royal Medical Board and the Swedish Royal Board of Social Affairs in 1968....

 in Sweden altered its standing regarding low-carbohydrate diets. Although formal endorsement of this regimen has not yet appeared, the government has given its formal approval for using carbohydrate-controlled diets for medically supervised weight loss.
U.S. Department of Health and Human Services
The HHS issues consumer guidelines for maintaining heart health which state regarding low-carbohydrate diets that "they're not the route to healthy, long-term weight management." Nevertheless HHS has issued some statements indicating wavering on this position.

Water-related weight loss


In the first week or two of a low-carbohydrate diet a great deal of the weight loss comes from eliminating water retained in the body (many doctors say that the presence of high levels of insulin in the blood causes unnecessary water retention in the body). However, this is a short-term effect and is entirely separate from the general weight loss that these diets can produce through eliminating excess body fat.

Exercise


Some critics argue that low-carbohydrate diets can inherently cause weakness or fatigue giving rise to the occasional assumption that low-carbohydrate dieting cannot involve an exercise regimen. Advocates of low-carbohydrate diets generally dispute any suggestion that such diets cause weakness or exhaustion (except in the first few days as the body adjusts) and indeed most highly recommend exercise as part of a healthy lifestyle. There is a large body of evidence stretching back to the 1880s that shows that physical performance is not negatively affected by ketogenic diets once a person has been acclimatized to such a diet. Arctic cultures such as the Inuit and African cultures such as the Maasai Tribesmen lead physically demanding lives and yet consume a diet almost completely devoid of carbohydrates. However, studies also indicate that while a low carbohydrate diet will not reduce endurance performance after adapting, they will probably deteriorate anaerobic performance such as strength training or sprint running because these processes rely on glycogen for fuel.
A living example that a ketogenic diet can indeed be combined with outstanding achievements in physical exercise is the Olympic biathlon gold medalist Björn Ferry, who won his gold medal after about 6 months on a low-carbohydrate high-fat diet.

Vegetables and fruits


Many critics argue that low-carbohydrate diets inherently require minimizing vegetable and fruit consumption which in turn robs the body of important nutrients. Some critics imply or explicitly argue that vegetables and fruits are inherently all heavily concentrated sources of carbohydrates (so much so that some sources literally treat the words vegetable and carbohydrate as synonymous). While some fruits may contain relatively high concentrations of sugar, most fruit is largely water and not particularly calorie-dense. Thus, in absolute terms, even sweet fruits and berries do not represent a significant source of carbohydrates in their natural form and also typically contain a good deal of fiber which attenuates the absorption of sugar in the gut and lastly, most of the sugar in fruit is fructose which, in obese subjects, has a reported negligible effect on insulin levels. Most vegetables are low- or moderate-carbohydrate foods (note that in the context of these diets 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...

 is excluded because it is not a nutritive carbohydrate). Some vegetables like potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...

es, rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...

, maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 (corn), and others, have high concentrations of starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

. Most low-carbohydrate diet plans accommodate vegetables such as broccoli
Broccoli
Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage"....

, spinach
Spinach
Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...

, cauliflower
Cauliflower
Cauliflower is one of several vegetables in the species Brassica oleracea, in the family Brassicaceae. It is an annual plant that reproduces by seed...

, and peppers
Capsicum
Capsicum is a genus of flowering plants in the nightshade family, Solanaceae. Its species are native to the Americas where they have been cultivated for thousands of years, but they are now also cultivated worldwide, used as spices, vegetables, and medicines - and have become are a key element in...

. The Atkins Diet recommends that most dietary carbs come from vegetables. Nevertheless debate remains as to whether restricting even just high-carbohydrate fruits, vegetables, and grains is truly healthy.

Contrary to the recommendations of most low-carbohydrate diet guides, some individuals may choose to avoid vegetables altogether in order to minimize carbohydrates. Low-carbohydrate vegetarianism
Vegetarianism
Vegetarianism encompasses the practice of following plant-based diets , with or without the inclusion of dairy products or eggs, and with the exclusion of meat...

 is also practiced. Carrot sticks and veggie sticks are especially useful in low carb diet recipes.

Raw fruits and vegetables are packed with array of other protective chemicals like vitamins, flavonoids or sugar alcohols. Some of those molecules can inhibit sugar absorption from intestines and provide other benefits in sugar control. Industrial food raffination
Raffinate
Raffinating something is a technique used in metallurgy to remove impurities from liquid material. There are many different kinds of raffination, for example you can use vacuum to extract hydrogen from metals....

 depletes some of those beneficial molecules in various degrees, including almost total removal in many cases.

Micronutrients and vitamins


The major low-carbohydrate diet guides generally recommend multi-vitamin and mineral supplements as part of the diet regimen which may lead some to believe that these diets are nutritionally deficient. The primary reason for this recommendation is that if the switch from a high-carbohydrate to a low-carbohydrate, ketogenic diet is rapid, the body can temporarily go through a period of adjustment during which the body may require extra vitamins and minerals (the reasons have to do with the body's releasing excess fluids that were stored during high-carbohydrate eating). In other words, the body goes through a temporary "shock" if the diet is changed to low-carbohydrate dieting quickly just as it would changing to a high-carbohydrate diet quickly. This does not, in and of itself, indicate that either type of diet is nutritionally deficient. While it is true that many foods that are rich in carbohydrates are also rich in vitamins and minerals, there are many low-carbohydrate foods that are similarly rich in vitamins and minerals.

Glucose availability


A common argument in favor of high-carbohydrate diets is that most carbohydrates break down readily into glucose in the bloodstream and, therefore, the body does not have to work as hard to get its energy in a high-carbohydrate diet as a low-carbohydrate diet. This argument, by itself, is incomplete. Although many dietary carbohydrates do break down into glucose, most of that glucose does not remain in the bloodstream for long. Its presence stimulates the beta cells in the pancreas to release insulin which has the effect of causing about 2/3 of body cells to take in glucose, and to cause fat cells to take in fatty acids and store them. As the blood glucose level falls, the amount of insulin released is reduced; the entire process is completed in non-diabetics in an hour or two after eating. High-carbohydrate diets require more insulin production and release than low-carbohydrate diets and there is some evidence that the increasingly large percentage of calories consumed as carbohydrates has led to the increased incidence of metabolic disorders such as type 2 diabetes.

In addition, this claim neglects the nature of the carbohydrates ingested. Some are indigestible in humans (e.g., cellulose), some are poorly digested in humans (e.g., the amylose starch variant), and some require considerable processing to be converted to absorbable forms. In general, uncooked or unprocessed (e.g., milling, crushing, etc.) foods are harder (typically much harder) to absorb and so do not raise glucose levels as much as might be expected from the proportion of carbohydrate present. Cooking (especially moist cooking above the temperature necessary to expand starch granules), and mechanical processing, both considerably raise the amount of absorbable carbohydrate and reduce the digestive effort required. Analyses which neglect these factors are misleading and will not result in a working diet, or at least one which works as intended. (See Catching Fire, Richard Wrangham)

In fact, there is some evidence that the human brain – the largest consumer of glucose in the body – can operate more efficiently on ketones.

Other controversies


In 2004, the Canadian government ruled that foods sold in Canada could not be marketed with reduced or eliminated carbohydrate content as a selling point because reduced carbohydrate content was not determined to be a health benefit, and that existing "low carb" and "no carb" packaging would have to be phased out by 2006.

Some variants of low carbohydrate diets involve substantially lowered intake of 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...

 which can result in constipation
Constipation
Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...

 if not supplemented. For example, this has been a criticism of the Induction phase of the Atkins diet (the Atkins diet is now clearer about recommending a fiber supplement during Induction). Most advocates today argue that fiber is a "good" carbohydrate and encourage a high-fiber diet.

It has been hypothesized that a diet-related change in blood acidity can lead to bone loss through a process called ketoacidosis
Ketoacidosis
Ketoacidosis is a metabolic state associated with high concentrations of ketone bodies, formed by the breakdown of fatty acids and the deamination of amino acids. The two common ketones produced in humans are acetoacetic acid and β-hydroxybutyrate....

, as mentioned earlier in this article. However ketoacidosis, which is often confused with ketosis, is an acute medical condition caused by extreme fasting or as a symptom of untreated diabetes, and is not likely to be induced by an otherwise adequate low-carbohydrate diet.

One of the occasional side effects of a ketogenic diet is a noticeable smell of ketones in the urine, perspiration, and breath. This is caused by the presence of larger than usual amounts of the three ketone bodies normally produced during fat metabolism. One of the ketone bodies, acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...

, is released via the lungs and has a characteristic smell of overripe fruit or nail polish remover. In most cases, periodic ketosis (as occurs between widely separated meals) does not cause a noticeable odor. When the other two ketone bodies are produced in large quantities in diabetic patients, the resulting condition is called ketoacidosis, and can be quite dangerous as even small changes in blood pH are life-threatening.

See also

  • Cyclic ketogenic diet
    Cyclic ketogenic diet
    A cyclic ketogenic diet is a low-carbohydrate diet with intermittent periods of high or moderate carbohydrate consumption. This is a form of the general Ketogenic diet that is used by bodybuilders as a way to maximize fat loss while also building body muscle. A ketogenic diet limits both the...

  • Diet
    Diet (nutrition)
    In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...

  • Glycemic index
    Glycemic 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...

  • Healthy diet
    Healthy diet
    A 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...

  • Insulin resistance
    Insulin resistance
    Insulin resistance is a physiological condition where the natural hormone insulin becomes less effective at lowering blood sugars. The resulting increase in blood glucose may raise levels outside the normal range and cause adverse health effects, depending on dietary conditions. Certain cell types...

  • Ketogenic diet
    Ketogenic 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...

    , a medically supervised diet used to treat epilepsy
    Epilepsy
    Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

  • List of diets
  • Low glycemic index diet
  • Medical research related to low-carbohydrate diets
    Medical research related to low-carbohydrate diets
    Low-carbohydrate diets became a major weight loss and health maintenance trend during the late 1990s and early 2000s. While their popularity has waned recently from its peak, they remain popular. This diet trend has stirred major controversies in the medical and nutritional sciences communities...

  • No-carbohydrate diet
    No-carbohydrate diet
    A no-carbohydrate diet is described as human carnivorism. It excludes dietary consumption of all carbohydrates and suggests fat as the main source of energy with sufficient protein...

  • Online weight loss plans
    Online weight loss plans
    Online 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...

  • Richard K. Bernstein
    Richard K. Bernstein
    Richard K. Bernstein, MD is a physician and an advocate for a low-carbohydrate diabetes diet to help achieve normal blood sugars for diabetics. Bernstein has type 1 diabetes. His private medical practice in Mamaroneck, New York is devoted solely to treating diabetes and prediabetes...

  • Richard D. Feinman
  • Shirataki noodles
    Shirataki noodles
    are very low carbohydrate, low calorie, thin, translucent, gelatinous traditional Japanese noodles made from devil's tongue yam . The word "shirataki" means "white waterfall", describing the appearance of these noodles...

  • High residue diet
    High 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...

  • Low residue diet
    Low residue diet
    A low residue diet is a diet designed to reduce the frequency and volume of stools while prolonging intestinal transit time. It is similar to a low fiber diet, but typically includes restrictions on foods that increase bowel activity, such as milk, milk products, and prune juice. A low residue diet...

  • 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...


Further reading