The term
underweight refers to a
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
who is considered to be under a healthy
weightIn the physical sciences, the weight of an object is the magnitude, W, of the force that must be applied to an object in order to support it in a gravitational field. The weight of an object in static equilibrium equals the magnitude of the gravitational force acting on the object, less the effect...
. The definition is usually made with reference to the
body mass indexThe body mass index , or Quetelet index, is a controversial statistical measurement which compares a person's weight and height. Though it does not actually measure the percentage of body fat, it may be a useful tool to estimate a healthy body weight based on how tall a person is...
(BMI). A BMI of under 18.5 is usually referred to as underweight. This medical definition of underweight may differ from other uses of the term, such as those based on
attractivenessAttractiveness, attractive quality or attraction refer to a quality to be the cause of the emotion of attraction in a person. An attraction emotion is an interest or desire in something or someone....
.
The most common cause of a person being underweight is primarily malnutrition caused by the unavailability of adequate food, which can run as high as 50% in parts of sub-Saharan Africa and south Asia.
The term
underweight refers to a
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
who is considered to be under a healthy
weightIn the physical sciences, the weight of an object is the magnitude, W, of the force that must be applied to an object in order to support it in a gravitational field. The weight of an object in static equilibrium equals the magnitude of the gravitational force acting on the object, less the effect...
. The definition is usually made with reference to the
body mass indexThe body mass index , or Quetelet index, is a controversial statistical measurement which compares a person's weight and height. Though it does not actually measure the percentage of body fat, it may be a useful tool to estimate a healthy body weight based on how tall a person is...
(BMI). A BMI of under 18.5 is usually referred to as underweight. This medical definition of underweight may differ from other uses of the term, such as those based on
attractivenessAttractiveness, attractive quality or attraction refer to a quality to be the cause of the emotion of attraction in a person. An attraction emotion is an interest or desire in something or someone....
.
Causes
The most common cause of a person being underweight is primarily malnutrition caused by the unavailability of adequate food, which can run as high as 50% in parts of sub-Saharan Africa and south Asia. The effects of primary malnutrition may be amplified by disease; even easily treatable diseases such as diarrhea may lead to death.
In the presence of adequate food resources, being underweight can sometimes be the result of mental or physical disease. There are hundreds of possible causes for excessive weight loss or a person being underweight. Some of the more prevalent include:
- Poverty
Poverty is the condition of lacking basic human needs such as nutrition, clean water, health care, clothing, and shelter because of the inability to afford them. This is also referred to as absolute poverty or destitution...
- Anorexia nervosa
Anorexia nervosa is a psychiatric illness that describes an eating disorder characterized by extremely low body weight and body image distortion with an obsessive fear of gaining weight...
- Bulimia nervosa
Bulimia nervosa is an eating disorder characterized by recurrent binge eating, followed by compensatory behaviors. The most common form is defensive vomiting, sometimes called purging; fasting, the use of laxatives, enemas, diuretics, and over exercising are also common.The word bulimia derives...
- Cancer
Cancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
or Cancer Treatment
- Tuberculosis
Tuberculosis is a common and often deadly infectious disease caused by mycobacteria...
- Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland,resulting in overproduction and thus an excess of circulating free thyroid hormones: thyroxine , triiodothyronine , or both...
- Type 1 Diabetes
- Anxiety
Anxiety is a psychological and physiological state characterized by cognitive, somatic, emotional, and behavioral components. These components combine to create an unpleasant feeling that is typically associated with uneasiness, fear, or worry....
and depressive disorders
- Drug use
Drugs can be used in many different ways, as detailed below.-Medication:People can use drugs to relieve pain or discomfort or to cure or prevent disease.-Recreational drug use:...
, especially stimulants
- Inflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis..-Forms:...
- Superior Mesenteric Artery Syndrome
Superior mesenteric artery syndrome is a very rare, life-threatening gastrointestinal disorder characterized by a compression of the third portion of the duodenum by the abdominal aorta and the overlying superior mesenteric artery...
- Malfunctioning digestive organs
- Dental pain
- Over-training (endurance sports)
- HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid,...
/AIDSAcquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus ....
- Genetics / Naturally light weight
- Puberty (height increases, body cannot catch up with muscle/fat growth)
Problems
The most immediate problem with underweight is that it might be secondary to, and/or symptomatic of, an underlying disease. Unexplained weight loss requires professional medical diagnosis.
Underweight can also be a primary causative condition. Severely underweight individuals may have poor physical stamina and a weak
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, leaving them open to
infectionAn infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply, usually at the expense of the host. The infecting organism, or pathogen, interferes with the normal functioning of the...
. According to Robert E. Black of the Johns Hopkins School of Public Health, "Underweight status ... and micronutrient deficiencies also cause decreases in immune and non-immune host defenses, and should be classified as underlying causes of death if followed by infectious diseases that are the terminal associated causes."
People who are malnutrative underweight raise special concerns, as not only gross caloric intake may be inadequate, but also intake and absorption of other vital nutrients, especially essential amino acids and micronutrients such as vitamins and minerals.
In women, being grossly underweight can result in amenorrhea (absence of menstruation) and possible complications during
pregnancyPregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Human pregnancy is the most studied of all mammalian pregnancies. Obstetrics is the surgical field...
. It can also cause anemia and hair loss.
Underweight is an established risk factor for
osteoporosisOsteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered...
, even for young people. This is a particular insidious consequence, because the affected persons do not notice the danger, they can feel fit and may be brilliant for example in endurance sports. After the occurrence of first spontaneous fractures the damage is often already irreversible.
Weight gain
If an individual is severely underweight to the point where problems with his or her health develop, it may be necessary for the person to make a concentrated effort to gain weight. The treatment for an underweight individual is to increase the
food energyFood energy is the amount of energy in food that is available through digestion.Like other forms of energy, food energy is expressed in calories or joules. Some countries use the food calorie, which is equal to 1 kilocalorie , or 1,000 gram calories...
intake so that more food energy is consumed than is being used as work. It is usually suggested that
weight trainingWeight training is a common type of strength training for developing the strength and size of skeletal muscles. It uses the force of gravity to oppose the force generated by muscle through concentric or eccentric contraction...
is also to be undertaken to increase
muscleMuscle is the contractile tissue of the body 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...
mass.
If weight loss results from a disease, resolving the illness and consuming adequate calories can bring many underweight individuals to a healthy body weight.
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