Adipose tissue

From Wikipedia, the free encyclopedia

 

Adipose tissue
Adipose tissue is one of the main types of connective tissue.
Pronunciation	/ˈædɪˌpoʊs/ (listen)
Identifiers
MeSH	D000273
FMA	20110

In biology, adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes.^[1] In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Adipose tissue is derived from preadipocytes. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body. Far from being hormonally inert, adipose tissue has, in recent years, been recognized as a major endocrine organ, as it produces hormones such as leptin, estrogen, resistin, and cytokine (especially TNFα). The two types of adipose tissue are white adipose tissue (WAT), which stores energy, and brown adipose tissue (BAT), which generates body heat. The formation of adipose tissue appears to be controlled in part by the adipose gene. Adipose tissue – more specifically brown adipose tissue – was first identified by the Swiss naturalist Conrad Gessner in 1551.

Anatomical features

In humans, adipose tissue is located: beneath the skin (subcutaneous fat), around internal organs (visceral fat), in bone marrow (yellow bone marrow), intermuscular (Muscular system) and in the breast (breast tissue). Adipose tissue is found in specific locations, which are referred to as adipose depots. Apart from adipocytes, which comprise the highest percentage of cells within adipose tissue, other cell types are present, collectively termed stromal vascular fraction (SVF) of cells. SVF includes preadipocytes, fibroblasts, adipose tissue macrophages, and endothelial cells. Adipose tissue contains many small blood vessels. In the integumentary system, which includes the skin, it accumulates in the deepest level, the subcutaneous layer, providing insulation from heat and cold. Around organs, it provides protective padding. However, its main function is to be a reserve of lipids, which can be oxidised to meet the energy needs of the body and to protect it from excess glucose by storing triglycerides produced by the liver from sugars, although some evidence suggests that most lipid synthesis from carbohydrates occurs in the adipose tissue itself.^[4] Adipose depots in different parts of the body have different biochemical profiles. Under normal conditions, it provides feedback for hunger and diet to the brain.

Mice

The obese mouse on the left has large stores of adipose tissue. It is unable to produce the hormone leptin. This causes the mouse to be hungry and eat more, which results in obesity. For comparison, a mouse with a normal amount of adipose tissue is shown on the right.

 

Mice have eight major adipose depots, four of which are within the abdominal cavity. The paired gonadal depots are attached to the uterus and ovaries in females and the epididymis and testes in males; the paired retroperitoneal depots are found along the dorsal wall of the abdomen, surrounding the kidney, and, when massive, extend into the pelvis. The mesenteric depot forms a glue-like web that supports the intestines and the omental depot (which originates near the stomach and spleen) and - when massive - extends into the ventral abdomen. Both the mesenteric and omental depots incorporate much lymphoid tissue as lymph nodes and milky spots, respectively.

The two superficial depots are the paired inguinal depots, which are found anterior to the upper segment of the hind limbs (underneath the skin) and the subscapular depots, paired medial mixtures of brown adipose tissue adjacent to regions of white adipose tissue, which are found under the skin between the dorsal crests of the scapulae. The layer of brown adipose tissue in this depot is often covered by a "frosting" of white adipose tissue; sometimes these two types of fat (brown and white) are hard to distinguish. The inguinal depots enclose the inguinal group of lymph nodes. Minor depots include the pericardial, which surrounds the heart, and the paired popliteal depots, between the major muscles behind the knees, each containing one large lymph node. Of all the depots in the mouse, the gonadal depots are the largest and the most easily dissected, comprising about 30% of dissectible fat.

Obesity

In an obese person, excess adipose tissue hanging downward from the abdomen is referred to as a panniculus. A panniculus complicates surgery of the morbidly obese individual. It may remain as a literal "apron of skin" if a severely obese person quickly loses large amounts of fat (a common result of gastric bypass surgery). Obesity is treated through exercise, diet, and behavioral therapy. Reconstructive surgery is one method of treatment.

Visceral fat

Abdominal obesity in men - beer belly

Visceral fat or abdominal fat (also known as organ fat or intra-abdominal fat) is located inside the abdominal cavity, packed between the organs (stomach, liver, intestines, kidneys, etc.). Visceral fat is different from subcutaneous fat underneath the skin, and intramuscular fat interspersed in skeletal muscles. Fat in the lower body, as in thighs and buttocks, is subcutaneous and is not consistently spaced tissue, whereas fat in the abdomen is mostly visceral and semi-fluid. Visceral fat is composed of several adipose depots, including mesenteric, epididymal white adipose tissue (EWAT), and perirenal depots. Visceral fat is often expressed in terms of its area in cm² (VFA, visceral fat area).

An excess of visceral fat is known as central obesity, or "belly fat", in which the abdomen protrudes excessively. New developments such as the Body Volume Index (BVI) are specifically designed to measure abdominal volume and abdominal fat. Excess visceral fat is also linked to type 2 diabetes, insulin resistance, inflammatory diseases, and other obesity-related diseases. Likewise, the accumulation of neck fat (or cervical adipose tissue) has been shown to be associated with mortality. Several studies have suggested that visceral fat can be predicted from simple anthropometric measures, and predicts mortality more accurately than body mass index or waist circumference.

Men are more likely to have fat stored in the abdomen due to sex hormone differences. Female sex hormone causes fat to be stored in the buttocks, thighs, and hips in women. When women reach menopause and the estrogen produced by the ovaries declines, fat migrates from the buttocks, hips and thighs to the waist; later fat is stored in the abdomen.

High-intensity exercise is one way to effectively reduce total abdominal fat. One study suggests at least 10 MET-hours per week of aerobic exercise is required for visceral fat reduction.

Epicardial fat

Epicardial adipose tissue (EAT) is a particular form of visceral fat deposited around the heart and found to be a metabolically active organ that generates various bioactive molecules, which might significantly affect cardiac function. Marked component differences have been observed in comparing EAT with subcutaneous fat, suggesting a depot specific impact of stored fatty acids on adipocyte function and metabolism.

Subcutaneous fat

Micro-anatomy of subcutaneous fat

 

Most of the remaining nonvisceral fat is found just below the skin in a region called the hypodermis. This subcutaneous fat is not related to many of the classic obesity-related pathologies, such as heart disease, cancer, and stroke, and some evidence even suggests it might be protective. The typically female (or gynecoid) pattern of body fat distribution around the hips, thighs, and buttocks is subcutaneous fat, and therefore poses less of a health risk compared to visceral fat.

Like all other fat organs, subcutaneous fat is an active part of the endocrine system, secreting the hormones leptin and resistin.^\

 

The relationship between the subcutaneous adipose layer and total body fat in a person is often modelled by using regression equations. The most popular of these equations was formed by Durnin and Wormersley, who rigorously tested many types of skinfold, and, as a result, created two formulae to calculate the body density of both men and women. These equations present an inverse correlation between skinfolds and body density—as the sum of skinfolds increases, the body density decreases.

Factors such as sex, age, population size or other variables may make the equations invalid and unusable, and, as of 2012, Durnin and Wormersley's equations remain only estimates of a person's true level of fatness. New formulae are still being created.

Marrow fat

Marrow fat, also known as marrow adipose tissue (MAT), is a poorly understood adipose depot that resides in the bone and is interspersed with hematopoietic cells as well as bony elements. The adipocytes in this depot are derived from mesenchymal stem cells (MSC) which can give rise to fat cells, bone cells as well as other cell types. The fact that MAT increases in the setting of calorie restriction/ anorexia is a feature that distinguishes this depot from other fat depots. The exercise regulation of marrow fat suggests that it bears some physiologic similarity to other white adipose depots. Moreover, increased MAT in obesity further suggests a similarity to white fat depots.

Ectopic fat

Ectopic fat is the storage of triglycerides in tissues other than adipose tissue, that are supposed to contain only small amounts of fat, such as the liver, skeletal muscle, heart, and pancreas. This can interfere with cellular functions and hence organ function and is associated with insulin resistance in type-2 diabetes. It is stored in relatively high amounts around the organs of the abdominal cavity, but is not to be confused with visceral fat.

The specific cause for the accumulation of ectopic fat is unknown. The cause is likely a combination of genetic, environmental, and behavioral factors that are involved in excess energy intake and decreased physical activity. Substantial weight loss can reduce ectopic fat stores in all organs and this is associated with an improvement of the function of that organ.

In the latter case, non-invasive weight loss interventions like diet or exercise can decrease ectopic fat (particularly in heart and liver) in overweight or obese children and adults.

Physiology

Free fatty acids (FFAs) are liberated from lipoproteins by lipoprotein lipase (LPL) and enter the adipocyte, where they are reassembled into triglycerides by esterifying them onto glycerol. Human fat tissue contains about 87% lipids.

There is a constant flux of FFAs entering and leaving adipose tissue. The net direction of this flux is controlled by insulin and leptin—if insulin is elevated, then there is a net inward flux of FFA, and only when insulin is low can FFA leave adipose tissue. Insulin secretion is stimulated by high blood sugar, which results from consuming carbohydrates.

In humans, lipolysis (hydrolysis of triglycerides into free fatty acids) is controlled through the balanced control of lipolytic B-adrenergic receptors and a2A-adrenergic receptor-mediated antilipolysis.

Fat cells have an important physiological role in maintaining triglyceride and free fatty acid levels, as well as determining insulin resistance. Abdominal fat has a different metabolic profile—being more prone to induce insulin resistance. This explains to a large degree why central obesity is a marker of impaired glucose tolerance and is an independent risk factor for cardiovascular disease (even in the absence of diabetes mellitus and hypertension). Studies of female monkeys at Wake Forest University (2009) discovered that individuals suffering from higher stress have higher levels of visceral fat in their bodies. This suggests a possible cause-and-effect link between the two, wherein stress promotes the accumulation of visceral fat, which in turn causes hormonal and metabolic changes that contribute to heart disease and other health problems.

Recent advances in biotechnology have allowed for the harvesting of adult stem cells from adipose tissue, allowing stimulation of tissue regrowth using a patient's own cells. In addition, adipose-derived stem cells from both human and animals reportedly can be efficiently reprogrammed into induced pluripotent stem cells without the need for feeder cells. The use of a patient's own cells reduces the chance of tissue rejection and avoids ethical issues associated with the use of human embryonic stem cells. A growing body of evidence also suggests that different fat depots (i.e. abdominal, omental, pericardial) yield adipose-derived stem cells with different characteristics. These depot-dependent features include proliferation rate, immunophenotype, differentiation potential, gene expression, as well as sensitivity to hypoxic culture conditions. Oxygen levels seem to play an important role on the metabolism and in general the function of adipose-derived stem cells.

Adipose tissue is a major peripheral source of aromatase in both males and females, contributing to the production of estradiol.

Adipose derived hormones include:

• Adiponectin
• Resistin
• Plasminogen activator inhibitor-1 (PAI-1)
• TNFα
• IL-6
• Leptin
• Estradiol (E2)

Adipose tissues also secrete a type of cytokines (cell-to-cell signalling proteins) called adipokines (adipose cytokines), which play a role in obesity-associated complications. Perivascular adipose tissue releases adipokines such as adiponectin that affect the contractile function of the vessels that they surround.

Brown fat

Brown fat or brown adipose tissue (BAT) is a specialized form of adipose tissue important for adaptive thermogenesis in humans and other mammals. BAT can generate heat by "uncoupling" the respiratory chain of oxidative phosphorylation within mitochondria through tissue-specific expression of uncoupling protein 1 (UCP1). BAT is primarily located around the neck and large blood vessels of the thorax, where may effectively act in heat exchange. BAT is robustly activated upon cold exposure by the release of catecholamines from sympathetic nerves that results in UCP1 activation. BAT activation may also occur in response to overfeeding. UCP1 activity is stimulated by long chain fatty acids that are produced subsequent to β-adrenergic receptor activation. UCP1 is proposed to function as a fatty acid proton symporter, although the exact mechanism has yet to be elucidated. In contrast, UCP1 is inhibited by ATP, ADP, and GTP.

Attempts to simulate this process pharmacologically have so far been unsuccessful. Techniques to manipulate the differentiation of "brown fat" could become a mechanism for weight loss therapy in the future, encouraging the growth of tissue with this specialized metabolism without inducing it in other organs.

Until recently, brown adipose tissue was thought to be primarily limited to infants in humans, but new evidence has now overturned that belief. Metabolically active tissue with temperature responses similar to brown adipose was first reported in the neck and trunk of some human adults in 2007, and the presence of brown adipose in human adults was later verified histologically in the same anatomical regions.

Beige fat and WAT browning

Morphology of three different classes of adipocytes

 

Browning of WAT, also referred to as "beiging", occurs when adipocytes within WAT depots develop features of BAT. Beige adipocytes take on a multilocular appearance (containing several lipid droplets) and increase expression of uncoupling protein 1 (UCP1). In doing so, these normally energy-storing adipocytes become energy-releasing adipocytes. 

The calorie-burning capacity of brown and beige fat has been extensively studied as research efforts focus on therapies targeted to treat obesity and diabetes. The drug 2,4-dinitrophenol, which also acts as a chemical uncoupler similarly to UCP1, was used for weight loss in the 1930s. However, it was quickly discontinued when excessive dosing led to adverse side effects including hyperthermia and death. β3 agonists, like CL316,243, have also been developed and tested in humans. However, the use of such drugs has proven largely unsuccessful due to several challenges, including varying species receptor specificity and poor oral bioavailability.

Cold is a primary regulator of BAT processes and induces WAT browning. Browning in response to chronic cold exposure has been well documented and is a reversible process. A study in mice demonstrated that cold-induced browning can be completely reversed in 21 days, with measurable decreases in UCP1 seen within a 24-hour period. A study by Rosenwald et al. revealed that when the animals are re-exposed to a cold environment, the same adipocytes will adopt a beige phenotype, suggesting that beige adipocytes are retained.

Transcriptional regulators, as well as a growing number of other factors, regulate the induction of beige fat. Four regulators of transcription are central to WAT browning and serve as targets for many of the molecules known to influence this process. These include peroxisome proliferator-activated receptor gamma (PPARγ), PR domain containing 16 (PRDM16), peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), and Early B-Cell Factor-2 (EBF2).

The list of molecules that influence browning has grown in direct proportion to the popularity of this topic and is constantly evolving as more knowledge is acquired. Among these molecules are irisin and fibroblast growth factor 21 (FGF21), which have been well-studied and are believed to be important regulators of browning. Irisin is secreted from muscle in response to exercise and has been shown to increase browning by acting on beige preadipocytes. FGF21, a hormone secreted mainly by the liver, has garnered a great deal of interest after being identified as a potent stimulator of glucose uptake and a browning regulator through its effects on PGC-1α. It is increased in BAT during cold exposure and is thought to aid in resistance to diet-induced obesity FGF21 may also be secreted in response to exercise and a low protein diet, although the latter has not been thoroughly investigated. Data from these studies suggest that environmental factors like diet and exercise may be important mediators of browning. In mice, it was found that beiging can occur through the production of methionine-enkephalin peptides by type 2 innate lymphoid cells in response to interleukin 33.

Genomics and bioinformatics tools to study browning

Due to the complex nature of adipose tissue and a growing list of browning regulatory molecules, great potential exists for the use of bioinformatics tools to improve study within this field. Studies of WAT browning have greatly benefited from advances in these techniques, as beige fat is rapidly gaining popularity as a therapeutic target for the treatment of obesity and diabetes.

DNA microarray is a bioinformatics tool used to quantify expression levels of various genes simultaneously, and has been used extensively in the study of adipose tissue. One such study used microarray analysis in conjunction with Ingenuity IPA software to look at changes in WAT and BAT gene expression when mice were exposed to temperatures of 28 and 6 °C. The most significantly up- and downregulated genes were then identified and used for analysis of differentially expressed pathways. It was discovered that many of the pathways upregulated in WAT after cold exposure are also highly expressed in BAT, such as oxidative phosphorylation, fatty acid metabolism, and pyruvate metabolism.^[74] This suggests that some of the adipocytes switched to a beige phenotype at 6 °C. Mössenböck et al. also used microarray analysis to demonstrate that insulin deficiency inhibits the differentiation of beige adipocytes but does not disturb their capacity for browning. These two studies demonstrate the potential for the use of microarray in the study of WAT browning. 

RNA sequencing (RNA-Seq) is a powerful computational tool that allows for the quantification of RNA expression for all genes within a sample. Incorporating RNA-Seq into browning studies is of great value, as it offers better specificity, sensitivity, and a more comprehensive overview of gene expression than other methods. RNA-Seq has been used in both human and mouse studies in an attempt characterize beige adipocytes according to their gene expression profiles and to identify potential therapeutic molecules that may induce the beige phenotype. One such study used RNA-Seq to compare gene expression profiles of WAT from wild-type (WT) mice and those overexpressing Early B-Cell Factor-2 (EBF2). WAT from the transgenic animals exhibited a brown fat gene program and had decreased WAT specific gene expression compared to the WT mice. Thus, EBF2 has been identified as a potential therapeutic molecule to induce beiging. 

Chromatin immunoprecipitation with sequencing (ChIP-seq) is a method used to identify protein binding sites on DNA and assess histone modifications. This tool has enabled examination of epigenetic regulation of browning and helps elucidate the mechanisms by which protein-DNA interactions stimulate the differentiation of beige adipocytes. Studies observing the chromatin landscapes of beige adipocytes have found that adipogenesis of these cells results from the formation of cell specific chromatin landscapes, which regulate the transcriptional program and, ultimately, control differentiation. Using ChIP-seq in conjunction with other tools, recent studies have identified over 30 transcriptional and epigenetic factors that influence beige adipocyte development.

Genetics

The thrifty gene hypothesis (also called the famine hypothesis) states that in some populations the body would be more efficient at retaining fat in times of plenty, thereby endowing greater resistance to starvation in times of food scarcity. This hypothesis, originally advanced in the context of glucose metabolism and insulin resistance, has been discredited by physical anthropologists, physiologists, and the original proponent of the idea himself with respect to that context, although according to its developer it remains "as viable as when [it was] first advanced" in other contexts.

In 1995, Jeffrey Friedman, in his residency at the Rockefeller University, together with Rudolph Leibel, Douglas Coleman et al. discovered the protein leptin that the genetically obese mouse lacked. Leptin is produced in the white adipose tissue and signals to the hypothalamus. When leptin levels drop, the body interprets this as a loss of energy, and hunger increases. Mice lacking this protein eat until they are four times their normal size.

Leptin, however, plays a different role in diet-induced obesity in rodents and humans. Because adipocytes produce leptin, leptin levels are elevated in the obese. However, hunger remains, and—when leptin levels drop due to weight loss—hunger increases. The drop of leptin is better viewed as a starvation signal than the rise of leptin as a satiety signal. However, elevated leptin in obesity is known as leptin resistance. The changes that occur in the hypothalamus to result in leptin resistance in obesity are currently the focus of obesity research.

Gene defects in the leptin gene (ob) are rare in human obesity. As of July 2010, only 14 individuals from five families have been identified worldwide who carry a mutated ob gene (one of which was the first ever identified cause of genetic obesity in humans)—two families of Pakistani origin living in the UK, one family living in Turkey, one in Egypt, and one in Austria—and two other families have been found that carry a mutated ob receptor. Others have been identified as genetically partially deficient in leptin, and, in these individuals, leptin levels on the low end of the normal range can predict obesity.

Several mutations of genes involving the melanocortins (used in brain signaling associated with appetite) and their receptors have also been identified as causing obesity in a larger portion of the population than leptin mutations.

Physical properties

Adipose tissue has a density of ~0.9 g/ml. Thus, a person with more adipose tissue will float more easily than a person of the same weight with more muscular tissue, since muscular tissue has a density of 1.06 g/ml.

Body fat meter

A body fat meter is a widely available tool used to measure the percentage of fat in the human body. Different meters use various methods to determine the body fat to weight ratio. They tend to under-read body fat percentage.

In contrast with clinical tools, one relatively inexpensive type of body fat meter uses the principle of bioelectrical impedance analysis (BIA) in order to determine an individual's body fat percentage. To achieve this, the meter passes a small, harmless, electric current through the body and measures the resistance, then uses information on the person's weight, height, age, and sex to calculate an approximate value for the person's body fat percentage. The calculation measures the total volume of water in the body (lean tissue and muscle contain a higher percentage of water than fat), and estimates the percentage of fat based on this information. The result can fluctuate several percentage points depending on what has been eaten and how much water has been drunk before the analysis. Before bioelectrical impedance analysis machines were developed, there were many different ways in analyzing body composition such as skin fold methods using calipers, underwater weighing, whole body air displacement plethysmography (ADP) and DXA.

Animal studies

Within the fat (adipose) tissue of CCR2 deficient mice, there is an increased number of eosinophils, greater alternative Macrophage activation, and a propensity towards type 2 cytokine expression. Furthermore, this effect was exaggerated when the mice became obese from a high fat diet.

Fat acceptance movement

From Wikipedia, the free encyclopedia

 

The sculpture Bronskvinnorna (The women of bronze) outside of the art museum (Konsthallen), Växjö, Sweden. The sculpture is a work by Marianne Lindberg De Geer. It displays one emaciated and one fat woman as a reaction to body fixation.

 

Women’s Sumo wrestling. There is modern day prejudice and sexism against it being played in tournaments

 

The fat acceptance movement (also known as fat pride, fat empowerment, and fat activism organiser)^{[citation needed]} is a social movement seeking to change anti-fat bias in social attitudes by raising awareness about obstacles faced by fat persons for the general public. Areas of contention include the aesthetic, legal, and medical approaches to people whose bodies are fatter than the social norm. 

The modern fat acceptance movement began in the late 1960s. Besides its political role, the fat acceptance movement also constitutes a subculture that acts as a social group for its members.

The movement has been criticized, with Cathy Young, writing for The Boston Globe, claiming that "the fat acceptance movement is hazardous to our health", and Barbara Kay, writing for the National Post, stating that "fat-acceptance is not the answer to obesity."

History

The history of the fat acceptance movement can be dated back to 1967 when 500 people met in New York's Central Park to protest against anti-fat bias. Sociologist Charlotte Cooper has argued that the history of the fat activist movement is best understood in waves, similar to the feminist movement, with which she believes it is closely tied. Cooper believes that fat activists have suffered similar waves of activism followed by burnout, with activists in a following wave often unaware of the history of the movement, resulting in a lack of continuity.

First wave

First wave activities consisted of isolated activists drawing attention to the dominant model of obesity and challenging it as only one of a number of possible models.

During the early part of the 20th century, obesity was seen as detrimental to the community, by means of decreasing human efficiency, and that obese people interfere with labor productivity in the coastal areas of the United States. This kind of history and visibility gave rise to the fat acceptance movement which originated in the late 1960s, although its grassroots nature makes it difficult to precisely chart its milestones. Like other social movements from this time period, the fat acceptance movement, initially known as "Fat Pride", "Fat Power", or "Fat Liberation", often consisted of people acting in an impromptu fashion. A "fat-in" was staged in New York's Central Park in 1967. Called by radio personality Steve Post, the "Fat-in" consisted of a group of 500 people eating, carrying signs and photographs of Sophia Loren (an actress famous for her figure), and burning diet books.

In 1967, Lew Louderback wrote an article in the Saturday Evening Post called "More People Should be FAT" in response to discrimination against his wife. The article led to a meeting between Louderback and William Fabrey, who went on to found the first organisation for fat people and their supporters, originally named the 'National Association to Aid Fat Americans' and currently called NAAFA ('National Association to Advance Fat Acceptance'). NAAFA was founded in America, in 1969, by Bill Fabrey in response to discrimination against his wife. He primarily intended it to campaign for fat rights, however a reporter attending the 2001 NAAFA conference notes that few attendees were active in fat rights politics and that most women came to shop for fashion, wear it on the conference catwalk or to meet a potential partner. Since 1991, Fabrey has worked as a director with the Council on Size and Weight Discrimination, specialising in the history of the size acceptance movement.

In 1972 the feminist group The Fat Underground was formed. It began as a radical chapter of NAAFA and spun off to become independent when NAAFA expressed concerns about its promotion of a stronger activist philosophy. The FU were inspired by and, in some cases, members of the Radical Therapy Collective, a feminist group that believed that many psychological problems were caused by oppressive social institutions and practices. Founded by Sara Fishman (then Sara Aldebaran) and Judy Freespirit, the Fat Underground took issue with what they saw as a growing bias against obesity in the scientific community. They coined the saying, "a diet is a cure that doesn't work, for a disease that doesn't exist". Shortly afterwards, Fishman moved to Connecticut, where, along with Karen Scott-Jones, she founded the New Haven Fat Liberation Front, an organization similar to the Fat Underground in its scope and focus. In 1983, the two groups collaborated to publish a seminal book in the field of fat activism, Shadow on a Tightrope, which collected several fat activist position papers initially distributed by the Fat Underground, as well as poems and essays from other writers.

In 1979 Carole Shaw coined the term Big Beautiful Woman (BBW) and launched a fashion and lifestyle magazine of the same name aimed at plus-sized women. The original print magazine closed in the late 1990s but the term BBW has become widely used to refer to any fat woman.

In the UK The London Fat Women's Group was formed, the first British fat activist group, and was active between approximately 1985 and 1989.

Other first wave activities included the productions of zines such as Figure 8 and Fat!So?, by Marilyn Wann which later became a book of the same name.

Second wave

In the second wave, the fat acceptance movement became more widespread in the USA and started to spread to other countries. Ideas from the movement began to appear in the mainstream. Publishers became more willing to publish fat acceptance themed literature.

By the 1990s, input from the fat acceptance movement began to be incorporated into research papers by some members of the medical professions such as new anti-dieting programs and models of obesity management.

The 1980s witnessed an increase in activist organizations, publications, and conferences. In 1989 a group of people including actress Anne Zamberlan formed the first French organisation for fat acceptance, Allegro fortissimo.

Organisations began holding conferences and conventions, including NAAFA.

Third wave

The fat acceptance movement has seen a diversification of projects during the third wave. Activities have addressed issues of both fat and race, class, sexuality and other issues. Size discrimination has been increasingly addressed in the arts, as well. Performance art groups such as Pretty Porky & Pissed Off, The Padded Lilies, a water ballet troupe of large sized women, Big Moves and the Fat Bottom Revue, a Big Burlesque touring show founded by fat activist, Heather MacAllister, and "LEFTOVERS, the Ups & Downs of a Compulsive Eater", by Marcia Kimmell, Deah Schwartz and Anne Wilford. These shows, among others, intentionally feature fat people in them.

The fat acceptance movement increased in the 2000s, with the creation of the "fatosphere" and the "Fat Liberation Feed", providing online communities of blogs and social media dedicated to the fat acceptance movement. Notable fat activists within the "fatosphere" include Marianne Kirby of The Rotund and Kate Harding of Shapely Prose, who co-wrote the book Lessons from the Fat-o-sphere: Quit Dieting and Declare a Truce with Your Body. Additionally, the Fat Studies listserv, Health At Every Size (HAES) was created by Marilyn Wann as a place for scholars to find more fat positive information. 

The individual blogs of the second wave have mainly been overtaken by larger scale social networking sites such as PeopleOfSize.com, while several websites have sprung up to help connect fat people with fat-friendly service providers and products, such as fatshionista. Size discrimination has been increasingly addressed in the arts, as well.

Campaigning themes

The fat acceptance movement argues that fat people are targets of hatred and discrimination. In particular, that obese women are subjected to more social pressure than obese men. The movement argues that these attitudes comprise a fat phobic entrenched societal norm, evident in many social institutions, including the mass media; where fat people are often ridiculed or held up as objects of pity. Discrimination includes lack of equal access to transportation and employment. Members of the fat acceptance movement perceive negative societal attitudes as persistent, and as being based on the presumption that fatness reflects negatively on a person's character. Fat activists continue to strive for change in societal, personal, and medical attitudes toward fat people. Fat acceptance organisations engage in public education about what they describe as myths concerning fat people.

Discrimination

Fat individuals claim to experience weight-based discrimination in a number of avenues within their lives. This discrimination is claimed to be experienced in healthcare, employment, education, interpersonal relationships, and in media.

Health

Fat activists argue that anti-fat stigma and aggressive diet promotion have led to an increase in psychological and physiological problems among fat people. Concerns are also raised that modern culture's focus on weight loss does not have a foundation in scientific research, but instead is an example of using science as a means to control deviance, as a part of society's attempt to deal with something that it finds disturbing. Diet critics cite the high failure rate of permanent weight loss attempts, and the dangers of "yo-yo" weight fluctuations and weight loss surgeries. Fat activists argue that the health issues of obesity and being overweight have been exaggerated or misrepresented, and that the health issues are used as a cover for cultural and aesthetic prejudices against fat.

Proponents of fat acceptance maintain that people of all shapes and sizes can strive for fitness and physical health. They believe health to be independent of body weight. Informed by this approach, psychologists who were unhappy with the treatment of fat people in the medical world initiated the Health at Every Size movement. It has five basic tenets: 1. Enhancing health, 2. Size and self-acceptance, 3. The pleasure of eating well, 4. The joy of movement, and 5. An end to weight bias.

However, the consensus within the scientific community is that obesity has a negative impact on the health of an individual. Numerous medical studies have challenged the 'healthy obesity' concept. One complicating factor in these studies is that definitions of metabolically-healthy obesity are not standardized across studies.

Gender

Fat women

Documentary filmmaker Kira Nerusskaya released her film The BBW World: Under the Fat! In 2008.

 

The issues faced by fat women in society have been a central theme of the fat acceptance movement since its inception. Although the first organisation, NAAFA, and the first book, Fat Power (1970), were both created by men, in each case they were responses to weight discrimination experienced by their wives. Women soon started campaigning on their own behalf with the first feminist group, 'The Fat Underground', being formed in 1973. Issues addressed regarding women have included body image, and in particular The Thin Ideal and its effect on women.

Fat men

The fat acceptance movement has primarily focused on a feminist model of patriarchal oppression of fat women, most clearly represented by the encouragement of women to diet. However, Sander L. Gilman argues that, until the 20th century, dieting has historically been a man's activity. He continues, "Obesity eats away at the idealised image of the masculine just as surely as it does the idealised image of the feminine." William Banting was the author of an 1863 booklet called Letter On Corpulence which modern diets have used as a model. Men respond to being overweight differently, (i.e., having a Body Mass Index of 25 or more), being half as likely as women to diet, a quarter as likely to undergo weightloss surgery and only a fifth as likely to report feeling shame about their weight. Irmgard Tischner identifies this behaviour as rooted in notions of masculinity that require a disregard for healthcare: "Men do not have to care about their size or health, as they have women to care about those things for them".

Some gay men have moved beyond disregard for size to fat acceptance and fat activism with movements like chub culture, which started as Girth & Mirth clubs in San Francisco in 1976^[56] and the bear culture which fetishises big, hairy men. Ganapati Durgadas argues that fat bisexual and gay men "are reminders of the feminine stigma with which heterosexism still tars queer men". In a comparison of queer fat positive zines, the lesbian-produced Fat Girl was found to have political debate content absent from gay male orientated zines such as Bulk Male and Big Ad. Joel Barraquiel Tan comments: "If fat is a feminist issue, then fat or heft is a fetishised one for gay men. Gay men have a tendency to sexualise difference, where lesbians have historically politicised it."

A fat heterosexual man is known as a "Big Handsome Man", in counterpart to a Big Beautiful Woman. Like some fat and gay men, BHMs have sexualized their difference and receive validation of this identity from BBWs or from straight women known as "Female Fat Admirers".

Legislation

In the 1980s fat people in the United States began seeking legal redress for discrimination on the basis of weight, primarily in the workplace but also for being denied access to, or treated differently in regards to, services or entertainment. The results of these cases has varied considerably, although in some instances the Americans with Disabilities Act (ADA) has been successfully used to argue cases of discrimination against fat people. Roth and Solovay argue that, as with transgender people, a major cause for the variation in success is the extent to which litigants are apologetic for their size:

What is the difference between a million-dollar weight case award and a losing case? Like the difference between many winning and losing transgender cases, it's all about the attitude. Does the claimant's attitude and experience about weight/gender reinforce or challenge dominant stereotypes? Winning cases generally adopt a legal posture that reinforces social prejudices. Cases that challenge societal prejudices generally lose.

The Americans with Disabilities Act continues to be used as there is no USA federal law against weight discrimination; however, the state of Michigan has passed a law against weight discrimination. The cities of Washington D.C., San Francisco (2000), Santa Cruz, Binghamton, Urbana (1990s) and Madison (1970s) have also passed laws prohibiting weight discrimination. In the cities that have a weight discrimination law it is rare for more than 1 case a year to be brought, except for San Francisco which may have as many as 6. Opinions amongst city enforcement workers vary as to why the prosecution numbers are so low, although they all suggested that both overweight people and employers were unaware of the protective legislation and it was also noted that the cities with anti-weight discrimination laws tended to be liberal college towns.

However, not all legal changes have protected the rights of fat people. Despite recommendations from the Equal Employment Opportunity Commission to the contrary, the United States Court of Appeals for the Sixth Circuit has decided that fat people will only qualify as disabled if it can be proved that their weight is caused by an underlying condition, supporting the concept that being obese is not inherently a disability.

Other countries besides the United States have considered legislation to protect the rights of fat people. In the UK an All Party Parliamentary Group published a report in 2012 called Reflections on Body Image that found that 1 in 5 British people had been victimised because of their weight. The report recommended that Members of Parliament Investigated putting "appearance-based discrimination" under the same legal basis as sexual or racial discrimination via the Equality Act 2010 which makes it illegal to harass, victimise or discriminate against anyone on the basis of a number of named categories. including size or weight.

Fat studies

There has also been an emerging body of academic studies with a fat activist agenda. Marilyn Wann argues that fat studies moved beyond being an individual endeavour to being a field of study with the 2004 conference Fat Attitudes: An Examination of an American Subculture and the Representation of the Female Body. The American Popular Culture Association regularly includes panels on the subject. In a number of colleges, student groups with a fat activist agenda have emerged, including Hampshire, Smith, and Antioch. Fat studies is now available as an interdisciplinary course of study at some colleges, taking a similar approach to other identity studies such as women's studies, queer studies and African American studies. As of 2011, there were 2 Australian courses and 10 American courses that were primarily focussed on fat studies or on health at every size, and numerous other courses that had some fat acceptance content. Taylor & Francis publish an online Fat Studies journal. In the UK, the first national Fat Studies seminar was held at York in May 2008, leading to the 2009 publication Fat Studies in the UK, edited by Corinna Tomrley and Ann Kalosky Naylor.

Debates within the movement

The fat acceptance movement has been divided in its response to proposed legislation defining morbidly obese people as disabled. NAAFA board member Peggy Howell says: "There's a lot of conflict in the size acceptance community over this. I don't consider myself disabled, and some people don't like 'fat' being considered a disability." An example of the positive perspective of obesity being classified as a disability in wider society is noted by one researcher: "She makes a point to tell me how impressed she is with the way many do make quiet and polite accommodations for her."

Another common division in the fat acceptance community is the differing attitudes towards general society, specifically thin people. The fat acceptance community generally divides into two categories. One is those who feel discrimination towards thin people hinders the fat acceptance cause. The other side views thin people as at least a partial cause of their social stigma.

Women are particularly active within the fat acceptance movement and membership of fat acceptance organizations is dominated by middle-class women in the heaviest 1–2% of the population. Members have criticized the lack of representation in the movement from men, people of color, and people of lower socioeconomic status.

Criticism

The fat acceptance movement has been criticised from a number of perspectives. Primarily there has been a conflict over the medicalisation of fat and health professionals who have criticised proponents of fat acceptance for ignoring health issues that many studies have shown to be linked to obesity. Fat acceptance has also been challenged from a moral perspective and the movement has been criticised for being out of touch with the mainstream.

Lionel Shriver, American journalist and author, wrote a column in Standpoint magazine strongly criticizing the fat acceptance movement. She condemned the movements' demand for respect for fatness in itself, which promotes the same unhealthy lifestyle that she believes killed her brother, who was morbidly obese and died at the age of 55. She also criticized the movements' repeated comparison of sizeism with racism or homophobia, saying that this approach casts obesity in the light of being an unchangeable state.

Cathy Young, writing for The Boston Globe, claimed that the movement was responsible for normalizing and promoting the acceptance of a controllable disease with clear health complications. While she recognizes the value in fighting against self-loathing, she draws the line at advocating for acceptance of an "unhealthy status quo." She says that by normalizing obesity, the fat acceptance movement leads people to underestimate the associated health hazards, and that the movement has also grown intolerant, exhibiting signs of elitism and treading on personal freedom.

The movement has also been criticized for its treatment of women with eating disorders or who follow diets for health-related reasons, since they are seen as betraying the movement. In 2008 Lily-Rygh Glen, a writer, musician, and former fat acceptance activist, interviewed multiple women who claimed to be rejected by their peers within the movement and labeled "traitors" when they changed their diets. One female activist admitted to living in fear that her binge eating disorder and consequent body image issues would be discovered. Glen states, "It is precisely because eating disorders are not openly discussed that many fat people who suffer from bulimia, binge-eating disorder, and pathorexia (defined as disordered appetite, and used to refer to an entire spectrum of disordered eating) feel they aren't welcome in the fat acceptance movement." The author also claimed that while in the process of interviewing and writing the article, which was featured in Bitch magazine's Lost & Found issue, she received wide condemnation from the fat acceptance community, and was labeled fatphobic and healthist.

Medical criticism

The fat acceptance movement has been criticized for not adding value to the debate over human health, with some critics accusing the movement of "promoting a lifestyle that can have dire health consequences". In 2018, the University of East Anglia released a report saying that fat acceptance, body positivity and the "normalization of plus size" was damaging to people's perceptions of obesity, made overweight and obese people less likely to seek medical attention when necessary, and undermined government initiatives intended to overcome the problem.

In response, proponents of fat acceptance claim that being fat in and of itself is not a health problem and that long-term weight-loss is unsuccessful in the majority of cases. There is however a considerable amount of evidence that overweight is associated with increased all-causes mortality, and significant weight loss (>10%), using a variety of diets, improves or reverses metabolic syndromes and other health outcomes associated with overweight and obesity. Barry Franklin, director of a cardio rehab facility states: "I don't want to take on any specific organisation but... A social movement that would suggest health at any size in many respects can be misleading". Fat acceptance campaigners also argue that current approaches constitute fat-shaming which, rather than leading to weight loss, results in psychological issues like eating disorders and more often functions counter-productively, resulting in weight gain.

Resting metabolic rate varies little between people, therefore, weight gain and loss are directly attributable to diet and activity. There is thus little evidence to support the view that some obese people eat little yet gain weight due to a slow metabolism; on average, obese people have a greater energy expenditure than their healthy-weight counterparts due to the energy required to maintain an increased body mass.

Body mass index

From Wikipedia, the free encyclopedia

 

Body mass index (BMI)
Medical diagnostics
A graph of body mass index as a function of body mass and body height. The dashed lines represent subdivisions within a major class.
Synonyms	Quetelet index
MeSH	D015992
MedlinePlus	007196
LOINC	39156-5

Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m², resulting from mass in kilograms and height in metres.

The BMI may be determined using a table or chart which displays BMI as a function of mass and height using contour lines or colours for different BMI categories, and which may use other units of measurement (converted to metric units for the calculation).

The BMI is a convenient rule of thumb used to broadly categorize a person as underweight, normal weight, overweight, or obese based on tissue mass (muscle, fat, and bone) and height. That categorization is the subject of some debate about where on the BMI scale the dividing lines between categories should be placed. Commonly accepted BMI ranges are underweight: under 18.5 kg/m², normal weight: 18.5 to 25, overweight: 25 to 30, obese: over 30.

BMIs under 20.0 and over 25.0 have been associated with higher all-causes mortality, with the risk increasing with distance from the 20.0–25.0 range.

History

Obesity and BMI

 

Adolphe Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, devised the basis of the BMI between 1830 and 1850 as he developed what he called "social physics". The modern term "body mass index" (BMI) for the ratio of human body weight to squared height was coined in a paper published in the July 1972 edition of the Journal of Chronic Diseases by Ancel Keys and others. In this paper, Keys argued that what he termed the BMI was "...if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity".

The interest in an index that measures body fat came with observed increasing obesity in prosperous Western societies. Keys explicitly judged BMI as appropriate for population studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnoses. Additional metrics, such as waist circumference, can be more useful.

The BMI is universally expressed in kg/m², resulting from mass in kilograms and height in metres. If pounds and inches are used, a conversion factor of 703 (kg/m²)/(lb/in²) must be applied. When the term BMI is used informally, the units are usually omitted.

${\displaystyle \mathrm {BMI} ={\frac {{\text{mass}}_{\text{kg}}}{{\text{height}}_{\text{m}}^{2}}}={\frac {{\text{mass}}_{\text{lb}}}{{\text{height}}_{\text{in}}^{2}}}\times 703}$

BMI provides a simple numeric measure of a person's thickness or thinness, allowing health professionals to discuss weight problems more objectively with their patients. BMI was designed to be used as a simple means of classifying average sedentary (physically inactive) populations, with an average body composition. For such individuals, the value recommendations as of 2014 are as follows: a BMI from 18.5 up to 25 kg/m² may indicate optimal weight, a BMI lower than 18.5 suggests the person is underweight, a number from 25 up to 30 may indicate the person is overweight, and a number from 30 upwards suggests the person is obese. Lean male athletes often have a high muscle-to-fat ratio and therefore a BMI that is misleadingly high relative to their body-fat percentage.

Scalability

BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the Ponderal index is based on the natural scaling of mass with the third power of the height.

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height. Carl Lavie has written that, "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."

Categories

A frequent use of the BMI is to assess how far an individual's body weight departs from what is normal or desirable for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI significantly (see discussion below and overweight).

The WHO regards a BMI of less than 18.5 as underweight and may indicate malnutrition, an eating disorder, or other health problems, while a BMI equal to or greater than 25 is considered overweight and above 30 is considered obese. These ranges of BMI values are valid only as statistical categories. 

Category	BMI (kg/m2)		BMI Prime
	from	to	from	to
Very severely underweight		15		0.60
Severely underweight	15	16	0.60	0.64
Underweight	16	18.5	0.64	0.74
Normal (healthy weight)	18.5	25	0.74	1.0
Overweight	25	30	1.0	1.2
Obese Class I (Moderately obese)	30	35	1.2	1.4
Obese Class II (Severely obese)	35	40	1.4	1.6
Obese Class III (Very severely obese)	40	45	1.6	1.8
Obese Class IV (Morbidly obese)	45	50	1.8	2
Obese Class V (Super obese)	50	60	2	2.4
Obese Class VI (Hyper obese)	60		2.4

Children (aged 2 to 20)

BMI for age percentiles for boys 2 to 20 years of age.

 

BMI for age percentiles for girls 2 to 20 years of age.

 

BMI is used differently for children. It is calculated in the same way as for adults, but then compared to typical values for other children of the same age. Instead of comparison against fixed thresholds for underweight and overweight, the BMI is compared against the percentiles for children of the same sex and age.

A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with a BMI between the 85th and 95th percentile are considered to be overweight.

Recent studies in Britain have indicated that females between the ages 12 and 16 have a higher BMI than males of the same age by 1.0 kg/m² on average.

International variations

These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. People from different ethnic groups, populations, and descent have different associations between BMI, percentage of body fat, and health risks, with a higher risk of type 2 diabetes mellitus and atherosclerotic cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m², although the cut-off for observed risk varies among different populations. The cut-off for observed risk varies based on populations and subpopulations both in Europe and Asia.

Hong Kong

The Hospital Authority of Hong Kong recommends the use of the following BMI ranges:

Category	BMI (kg/m2)
	from	to
Underweight		18.5
Normal Range	18.5	23
Overweight—At Risk	23	25
Overweight—Moderately Obese	25	30
Overweight—Severely Obese	30

Japan

Japan Society for the Study of Obesity (2000):

Category	BMI (kg/m2)
	from	to
Low		18.5
Normal	18.5	25
Obese (Level 1)	25	30
Obese (Level 2)	30	35
Obese (Level 3)	35	40
Obese (Level 4)	40

Singapore

In Singapore, the BMI cut-off figures were revised in 2005, motivated by studies showing that many Asian populations, including Singaporeans, have higher proportion of body fat and increased risk for cardiovascular diseases and diabetes mellitus, compared with general BMI recommendations in other countries. The BMI cut-offs are presented with an emphasis on health risk rather than weight. 

Health Risk	BMI (kg/m2)
Risk of developing problems such as nutritional deficiency and osteoporosis	under 18.5
Low Risk (healthy range)	18.5 to 23
Moderate risk of developing heart disease, high blood pressure, stroke, diabetes	23 to 27.5
High risk of developing heart disease, high blood pressure, stroke, diabetes	over 27.5

United States

In 1998, the U.S. National Institutes of Health and the Centers for Disease Control and Prevention brought U.S. definitions in line with World Health Organization guidelines, lowering the normal/overweight cut-off from BMI 27.8 to BMI 25. This had the effect of redefining approximately 29 million Americans, previously healthy, to overweight.

This can partially explain the increase in the overweight diagnosis in the past 20 years, and the increase in sales of weight loss products during the same time. WHO also recommends lowering the normal/overweight threshold for South East Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types.

The U.S. National Health and Nutrition Examination Survey of 1994 showed that 59.8% of American men and 51.2% of women had BMIs over 25. Morbid obesity—a BMI of 40 or more—was found in 2% of the men and 4% of the women. A survey in 2007 showed 63% of Americans are overweight or obese, with 26% in the obese category (a BMI of 30 or more). As of 2014, 37.7% of adults in the United States were obese, categorized as 35.0% of men and 40.4% of women; class 3 obesity (BMI over 40) values were 7.7% for men and 9.9% for women.

Body Mass Index values for males and females aged 20 and over, and selected percentiles by age: United States, 2011–2014.

Age	Percentile
	5th	10th	15th	25th	50th	75th	85th	90th	95th
	Men BMI (kg/m2)
20 years and over (total)	20.7	22.2	23.0	24.6	27.7	31.6	34.0	36.1	39.8
20–29 years	19.3	20.5	21.2	22.5	25.5	30.5	33.1	35.1	39.2
30–39 years	21.1	22.4	23.3	24.8	27.5	31.9	35.1	36.5	39.3
40–49 years	21.9	23.4	24.3	25.7	28.5	31.9	34.4	36.5	40.0
50–59 years	21.6	22.7	23.6	25.4	28.3	32.0	34.0	35.2	40.3
60–69 years	21.6	22.7	23.6	25.3	28.0	32.4	35.3	36.9	41.2
70–79 years	21.5	23.2	23.9	25.4	27.8	30.9	33.1	34.9	38.9
80 years and over	20.0	21.5	22.5	24.1	26.3	29.0	31.1	32.3	33.8
Age	Women BMI (kg/m2)
20 years and over (total)	19.6	21.0	22.0	23.6	27.7	33.2	36.5	39.3	43.3
20–29 years	18.6	19.8	20.7	21.9	25.6	31.8	36.0	38.9	42.0
30–39 years	19.8	21.1	22.0	23.3	27.6	33.1	36.6	40.0	44.7
40–49 years	20.0	21.5	22.5	23.7	28.1	33.4	37.0	39.6	44.5
50–59 years	19.9	21.5	22.2	24.5	28.6	34.4	38.3	40.7	45.2
60–69 years	20.0	21.7	23.0	24.5	28.9	33.4	36.1	38.7	41.8
70–79 years	20.5	22.1	22.9	24.6	28.3	33.4	36.5	39.1	42.9
80 years and over	19.3	20.4	21.3	23.3	26.1	29.7	30.9	32.8	35.2

Consequences of elevated level in adults

The BMI ranges are based on the relationship between body weight and disease and death.^[26] Overweight and obese individuals are at an increased risk for the following diseases:^[27]

• Coronary artery disease
• Dyslipidemia
• Type 2 diabetes
• Gallbladder disease
• Hypertension
• Osteoarthritis
• Sleep apnea
• Stroke
• At least 10 cancers, including endometrial, breast, and colon cancer.
• Epidural lipomatosis 

Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight.

Applications

Public health

The BMI is generally used as a means of correlation between groups related by general mass and can serve as a vague means of estimating adiposity. The duality of the BMI is that, while it is easy to use as a general calculation, it is limited as to how accurate and pertinent the data obtained from it can be. Generally, the index is suitable for recognizing trends within sedentary or overweight individuals because there is a smaller margin of error. The BMI has been used by the WHO as the standard for recording obesity statistics since the early 1980s. 

This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the RDA for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, due to the fact that the majority of children are sedentary. Cross-sectional studies indicated that sedentary people can decrease BMI by becoming more physically active. Smaller effects are seen in prospective cohort studies which lend to support active mobility as a means to prevent a further increase in BMI.

Clinical practice

BMI categories are generally regarded as a satisfactory tool for measuring whether sedentary individuals are underweight, overweight, or obese with various exceptions, such as: athletes, children, the elderly, and the infirm. Also, the growth of a child is documented against a BMI-measured growth chart. Obesity trends can then be calculated from the difference between the child's BMI and the BMI on the chart. In the United States, BMI is also used as a measure of underweight, owing to advocacy on behalf of those with eating disorders, such as anorexia nervosa and bulimia nervosa.

Legislation

In France, Italy, and Spain, legislation has been introduced banning the usage of fashion show models having a BMI below 18. In Israel, a BMI below 18.5 is banned. This is done to fight anorexia among models and people interested in fashion.

Limitations

This graph shows the correlation between body mass index (BMI) and percent body fat (%BF) for 8550 men in NCHS' NHANES 1994 data. Data in the upper left and lower right quadrants suggest the limitations of BMI.

 

The medical establishment and statistical community have both highlighted the limitations of BMI.

Scaling

The exponent in the denominator of the formula for BMI is arbitrary. The BMI depends upon weight and the square of height. Since mass increases to the third power of linear dimensions, taller individuals with exactly the same body shape and relative composition have a larger BMI.

According to mathematician Nick Trefethen, "BMI divides the weight by too large a number for short people and too small a number for tall people. So short people are misled into thinking that they are thinner than they are, and tall people are misled into thinking they are fatter."

For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females.

Physical characteristics

The BMI overestimates roughly 10% for a large (or tall) frame and underestimates roughly 10% for a smaller frame (short stature). In other words, persons with small frames would be carrying more fat than optimal, but their BMI indicates that they are normal. Conversely, large framed (or tall) individuals may be quite healthy, with a fairly low body fat percentage, but be classified as overweight by BMI.

For example, a height/weight chart may say the ideal weight (BMI 21.5) for a man 5 ft 10 in (178 cm) is 150 pounds (68 kg). But if that man has a slender build (small frame), he may be overweight at 150 pounds (68 kg) and should reduce by 10%, to roughly 135 pounds (61 kg) (BMI 19.4). In the reverse, the man with a larger frame and more solid build should increase by 10%, to roughly 165 pounds (75 kg) (BMI 23.7). If one teeters on the edge of small/medium or medium/large, common sense should be used in calculating one's ideal weight. However, falling into one's ideal weight range for height and build is still not as accurate in determining health risk factors as waist-to-height ratio and actual body fat percentage.

Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference and others) to determine what category an individual falls into for a given height. The BMI also fails to take into account loss of height through aging. In this situation, BMI will increase without any corresponding increase in weight.

A new formula, that accounts for the distortions of BMI at high and low heights, has been suggested: BMI = 1.3*weight(kg)/height(m)^2.5.

Muscle versus fat

Assumptions about the distribution between muscle mass and fat mass are inexact. BMI generally overestimates adiposity on those with more lean body mass (e.g., athletes) and underestimates excess adiposity on those with less lean body mass.

A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from the United States' third National Health and Nutrition Examination Survey (NHANES III) and found that BMI-defined obesity (BMI > 30) was present in 21% of men and 31% of women. Body fat-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high specificity (95% for men and 99% for women), BMI showed poor sensitivity (36% for men and 49% for women). In other words, BMI is better at determining a person is not obese than it is at determining a person is obese. Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%.

BMI is particularly inaccurate for people who are very fit or athletic, as their high muscle mass can classify them in the overweight category by BMI, even though their body fat percentages frequently fall in the 10–15% category, which is below that of a more sedentary person of average build who has a normal BMI number. For example, the BMI of bodybuilder and eight-time Mr. Olympia Ronnie Coleman was 41.8 at his peak physical condition, which would be considered morbidly obese. Body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to new, alternative methods to measure obesity, such as the body volume index.

Variation in definitions of categories

It is not clear where on the BMI scale the threshold for overweight and obese should be set. Because of this the standards have varied over the past few decades. Between 1980 and 2000 the U.S. Dietary Guidelines have defined overweight at a variety of levels ranging from a BMI of 24.9 to 27.1. In 1985 the National Institutes of Health (NIH) consensus conference recommended that overweight BMI be set at a BMI of 27.8 for men and 27.3 for women.

In 1998 a NIH report concluded that a BMI over 25 is overweight and a BMI over 30 is obese. In the 1990s the World Health Organization (WHO) decided that a BMI of 25 to 30 should be considered overweight and a BMI over 30 is obese, the standards the NIH set. This became the definitive guide for determining if someone is overweight. 

The current WHO and NIH ranges of normal weights are proved to be associated with decreased risks of some diseases such as diabetes type II; however using the same range of BMI for men and women is considered arbitrary, and makes the definition of underweight quite unsuitable for men.

One study found that the vast majority of people labelled 'overweight' and 'obese' according to current definitions do not in fact face any meaningful increased risk for early death. In a quantitative analysis of a number of studies, involving more than 600,000 men and women, the lowest mortality rates were found for people with BMIs between 23 and 29; most of the 25–30 range considered 'overweight' was not associated with higher risk.

Relationship to health

A study published by Journal of the American Medical Association (JAMA) in 2005 showed that overweight people had a death rate similar to normal weight people as defined by BMI, while underweight and obese people had a higher death rate.

A study published by The Lancet in 2009 involving 900,000 adults showed that overweight and underweight people both had a mortality rate higher than normal weight people as defined by BMI. The optimal BMI was found to be in the range of 22.5–25.

High BMI is associated with type 2 diabetes only in persons with high serum gamma-glutamyl transpeptidase.

In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the overweight range (BMI 25–29.9).

One study found that BMI had a good general correlation with body fat percentage, and noted that obesity has overtaken smoking as the world's number one cause of death. But it also notes that in the study 50% of men and 62% of women were obese according to body fat defined obesity, while only 21% of men and 31% of women were obese according to BMI, meaning that BMI was found to underestimate the number of obese subjects.

A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI is not a good measure for the risk of heart attack, stroke or death. A better measure was found to be the waist-to-height ratio. A 2011 study that followed 60,000 participants for up to 13 years found that waist–hip ratio was a better predictor of ischaemic heart disease mortality.

Alternatives

BMI prime

BMI prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25 kg/m²), i.e., the actual BMI expressed as a proportion of upper limit optimal. The ratio of actual body weight to body weight for upper limit optimal BMI (25 kg/m²) is equal to BMI Prime. BMI Prime is a dimensionless number independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34 kg/m² has a BMI Prime of 34/25 = 1.36, and is 36% over their 

upper mass limit. In South East Asian and South Chinese populations (see § international variations), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.

Waist circumference

Waist circumference is a good indicator of visceral fat, which poses more health risks than fat elsewhere. According to the U.S. National Institutes of Health (NIH), waist circumference in excess of 102 centimetres (40 in) for men and 88 centimetres (35 in) for (non-pregnant) women, is considered to imply a high risk for type 2 diabetes, dyslipidemia, hypertension, and CVD. Waist circumference can be a better indicator of obesity-related disease risk than BMI. For example, this is the case in populations of Asian descent and older people. 94 centimetres (37 in) for men and 80 centimetres (31 in) for women has been stated to pose "higher risk", with the NIH figures "even higher".

Waist-to-hip circumference ratio has also been used, but has been found to be no better than waist circumference alone, and more complicated to measure.

A related indicator is waist circumference divided by height. The values indicating increased risk are: greater than 0.5 for people under 40 years of age, 0.5 to 0.6 for people aged 40–50, and greater than 0.6 for people over 50 years of age.

Surface-based body shape index

The Surface-based Body Shape Index (SBSI) is far more rigorous and is based upon four key measurements: the body surface area (BSA), vertical trunk circumference (VTC), waist circumference (WC) and height (H). Data on 11,808 subjects from the National Health and Human Nutrition Examination Surveys (NHANES) 1999–2004, showed that SBSI outperformed BMI, waist circumference, and A Body Shape Index (ABSI), an alternative to BMI.

${\displaystyle \mathrm {SBSI} ={\frac {({\text{H}}^{7/4})({\text{WC}}^{5/6})}{\text{BSA VTC}}}}$

A simplified, dimensionless form of SBSI, known as SBSI^*, has also been developed.

${\displaystyle \mathrm {SBSI^{\star }} ={\frac {({\text{H}}^{2})({\text{WC}})}{\text{BSA VTC}}}}$

Modified body mass index

Within some medical contexts, such as familial amyloid polyneuropathy, serum albumin is factored in to produce a modified body mass index (mBMI). The mBMI can be obtained by multiplying the BMI by serum albumin, in grams per litre.