"The price of greatness is responsibility." Sir Winston Churchill

From Wikipedia, the free encyclopedia.

Obesity is a condition where the natural energy reserve, stored in the fatty tissue of humans and mammals is increased to the point where it may impair health. Obesity in wild animals is relatively rare, but it is common in domestic animals like pigs and household pets who may be overfed and underexercised. In humans it is generally considered to be a leading cause of health problems.

While scientific and cultural definitions of obesity are subject to change, it is accepted that excessive body weight predisposes to various forms of disease, particularly cardiovascular disease. Interventions, such as weight loss and medication, are frequently recommended to reduce this risk, although its exact benefits are uncertain, and many people undertake weight loss regimens for health as well as aesthetic reasons.

Contents [hide] 1 Definition 2 Etymology 3 Cultural and social significance 3.1 Culture and obesity 3.2 Popular culture 4 Causes 4.1 Causative factors 4.2 Evolutionary aspects 4.3 Neurobiological mechanisms 4.4 Societal causes 4.5 Poverty link 5 Complications 6 Therapy 7 Controversies 7.1 Medicalization of obesity 7.2 Health effects of obesity 7.3 Medical responses to obesity 7.4 Prevalence and public interest 7.5 Policy responses to obesity 8 See also 9 References 10 External links

 

Definition

Obesity
ICD-10 code:	E66
ICD-9 code:	278

Obesity is a concept that is being continually redefined. In humans, the most common statistical estimate of obesity is the body mass index (BMI), calculated by dividing the weight by the height squared; its unit is therefore kg/m², although no actual surface is implied. The BMI was created in the 19th century by the Belgian statistician Adolphe Quetelet.

Interpretation of the BMI:

• A person with a BMI over 25.0 kg/m² is considered overweight.
• A BMI over 30.0 kg/m² denotes obesity.
• A further threshold at 40.0 kg/m² is identified as urgent morbidity risk (morbid obesity).

The American Institute for Cancer Research considers a BMI between 18.5 and 25 to be an ideal target for a healthy individual (although several sources consider a person with a BMI of less than 20 to be underweight).

The cut-off points between categories are occasionally redefined, and may indeed differ from country to country. In June 1998 the National Institutes of Health brought official U.S. category definitions into line with those used by the WHO, moving the American "overweight" threshold from BMI 27 to BMI 25. About 30,000,000 Americans moved from "ideal" weight to being 1–10 pounds (0.5–5 kg) "overweight". In 2000, WHO was advised to consider lowering the BMI threshold for overweight in Asians from BMI 25 to BMI 23, and for obesity in Asians from BMI 30 to BMI 25, due to epidemiological studies indicating that Asians suffer a greater number of obesity-related conditions at lower BMI; however, to date, WHO has not made any changes in recommendations. In addition, some clinicians suggest raising the BMI thresholds for those of African, African-American, and Polynesian descent because members of these groups have a greater ratio of lean body mass to fat at all body weights; the proposed thresholds for these groups are BMI 26 for overweight, and BMI 32 for obesity. To date, no major professional or medical organization has officially adopted this suggestion. In future, healthy BMI for a given individual may be defined to some extent by his ethnic or racial origin.

As a result of this somewhat arbitrary process, the BMI cannot offer a complete diagnosis, in that it ignores fat distribution within the body (see central obesity), and the relative fat-muscle-bone contributions to total body weight. A powerful athlete may be classified as obese by the BMI due to heavy musculature, while a false-normal may be diagnosed in the case of an elderly person with very low lean mass, which masks excess adiposity. On its own, a BMI score is therefore inadequate as a diagnostic tool.

In practice, in most examples of overweightness that may be harmful to health, both doctor and patient can see "by eye" that fat is an issue. In these cases, BMI thresholds provide simple targets all patients can understand. Doctors may also use a simple measure of waist circumference (which is a better predictor of complications such insulin resistance due to visceral fat^[1]); the skinfold test, in which a pinch of skin is precisely measured to determine the thickness of the subcutaneous fat layer; or bioelectrical impedance analysis, usually only carried out at specialist clinics.

Such clinical data is rarely available in the statistical raw materials required for large public health studies, however — whereas height and weight is commonly recorded. For this essential reason, BMI remains the most commonly-used approach for public health studies, and the most useful for cross-border, longitudinal, and other types of comparative analysis.

 

Etymology

Obesity is the nominal form of obese which comes from the Latin obēsus, which means "stout, fat, or plump." Ēsus is the past participle of edere (to eat), with ob added to it. In Classical Latin, this verb is seen only in past participial form. Its first attested usage in English was in 1651, in N. Biggs' Matæotechnia Medicinæ Praxeuus^[2].

 

Cultural and social significance

 

Culture and obesity

In several human cultures, obesity is associated with attractiveness, strength, and fertility. Some of the earliest known cultural artifacts, known as Venuses, are pocket-sized statuettes representing an obese female figure. Although their cultural significance is unrecorded, their widespread use throughout pre-historic Mediterranean and European cultures suggests a central role for the obese female form in magical rituals, and implies cultural approval of (and perhaps reverence for) this body form.

In comparison to Western Culture, the young and slender woman is seen and desired by both men and women. It can be seen as more important for women than men. "Although the female body is predisposed to proportionately more fat and the male to more muscle, the plump or stout woman's body is considered neither beautiful nor sexually attractive."^[3]

Obesity functions as a symbol of wealth and success in cultures prone to food scarcity. Well into the early modern period in European cultures, it still served this role. But as food security was realised, it came to serve more as a visible signifier of "lust for life", appetite, and immersion in the realm of the erotic. This was especially the case in the visual arts, such as the paintings of Rubens (1577–1640), whose regular use of the full female figures gives us the description Rubenesque for plumpness. Obesity can also be seen as symbol for a system of prestige. "The kind of food, the quantity, and the manner in which it is served are among the important criteria of social class. In most tribal societies, even those with a highly stratified social system, everyone - royalty and the commoners - ate the same kind of food, and if there was famine everyone was hungry. With the ever increasing diversity of foods, food has become not only a matter of social status, but also a mark of one's personality and taste."^[4]

Contemporary cultures which approve of obesity, to a greater or lesser degree, include African, Arabic, Indian, and Pacific Island cultures. In Western cultures, obesity has come to be seen more as a medical condition than as a social statement. In American culture, many use a popular snap, "Yo' momma's so fat...", in playing "the dozens". A small minority of activists, especially clustered around the tradition of feminism, seek through the fat acceptance movement to challenge that emerging consensus.

There are some who are trying to combat the problem of obesity. In American society, "we have indicated a number of strong trends in our culture which run counter to obesity. The desire for health, for longevity, for youthfulness, for sexual attractiveness is indeed a powerful motivation."^[5]

 

Popular culture

Various stereotypes of obese people have found their way into expressions of popular culture. A common stereotype is the obese character who has a warm and dependable personality, presumedly in compensation for social exclusion, but equally common is the obese vicious bully. Gluttony and obesity are commonly depicted together in works of fiction. In cartoons, obesity is used to comedic effect, with fat cartoon characters having to squeeze through narrow spaces, frequently getting stuck.

It can be argued that depiction in popular culture adds to and maintains commonly perceived stereotypes, in turn harming self esteem of obese people. A charge of discrimination on the basis of appearance could be leveled against these depictions.

On the other hand, obesity is often associated with positive characteristics such as good humor (the stereotype of the jolly fat man like Santa Claus), and some people are more sexually attracted to obese people than to slender people (see chubby culture, fat admirer).

 

Causes

 

Causative factors

Obesity is believed to be caused by excessive caloric intake accompanied with insufficient caloric expenditure. Factors that may contribute to this imbalance include:

• Limited exercise and sedentary lifestyle
• Genetic predisposition
• A high glycemic diet (i.e. a diet that consists of meals that give high postprandial blood sugar)
• Weight cycling, caused by repeated attempts to lose weight by dieting
• Underlying illness (e.g. hypothyroidism)
• An eating disorder (such as binge eating disorder)
• Stressful mentality
• Insufficient sleeping
• Psychotropic medications

As with many medical conditions, obesity often develops from a combination of genetic and environmental factors. Polymorphisms in various genes controlling appetite, rate of metabolism, and adipokine release predispose to obesity, but the condition, to some extent, requires availability of sufficient calories and/or limited exercise, and possibly other factors, to develop fully. Various genetic abnormalities that predispose to obesity have been identified (such as Prader-Willi syndrome and leptin receptor mutations), but these are absent in most people with obesity. It is presumed that a large proportion of the causative genes are still to be identified.

Some eating disorders can lead to obesity, especially binge eating disorder (BED). As the name indicates, patients with this disorder are prone to overeat, often in binges. A proposed mechanism is that the eating serves to reduce anxiety, and some parallels with substance abuse can be drawn. An important additional factor is that BED patients often lack the ability to recognize hunger and satisfaction, something that is normally learned in childhood. Learning theory suggests that early childhood conceptions may lead to an association between food and a calm mental state.

 

Evolutionary aspects

Although there is no definitive explanation for the recent increase of obesity, the evolutionary hypothesis comes closest to providing some understanding of this phenomenon. In times when food was scarce, the ability to take advantage of rare periods of abundance and use such abundance by storing energy efficiently was undoubtedly an evolutionary advantage. This is precisely the opposite of what is required in a sedentary society, where high-energy food is available in abundant quantities in the context of decreased exercise. Although many people may have a genetic propensity towards obesity, it is only with the reduction in physical activity and a move towards high-calorie diets of modern society that it has become widespread.

 

Neurobiological mechanisms

Flier^[6] summarizes the many possible pathophysiological mechanisms involved in the development and maintenance of obesity. This field of research had been almost unapproached until leptin was discovered in 1994. Since this discovery, many other hormonal mechanisms have been proposed that participate in the regulation of appetite and food intake, storage patterns of adipose tissue, development of insulin resistance, and possible ways of interfering with these mechanisms. Since leptin's discovery, ghrelin, orexin, PYY 3-36, cholecystokinin, adiponectin, and numerous other mediators have been studied. The adipokines are mediators produced by adipose tissue; their action is thought to modify many obesity-related diseases.

Leptin and ghrelin are considered to be complementary in their influence on appetite, with the stomach producing ghrelin when relatively empty and leptin being produced by adipose tissue when satiated with nutrients. Resistance to the leptin signal and causes for this resistance have been implicated in dysregulation of appetite, although administration of leptin has not proven to be a feasible way of suppressing appetite in humans.

Neuroscientific approaches hinge on the action of the aforementioned hormones and mediators on the hypothalamus, the part of the brain that is thought to produce hunger signals for higher centers and induce food intake behavior. Lesion studies in the 1940s and 1950s identified two regions of the hypothalamus — the lateral hypothalamus (LH) and ventromedial hypothalamus (VMH) — as the brain's hunger and satiety centers, respectively. Specific lesions to a mouse's LH suppressed its appetite while damaging the VMH caused overeating.

Studies of the distribution of the leptin receptor in the mid-1990s cast doubt upon this dual center theory of hunger and satiety. Leptin's effect on the arcuate nucleus melanocortin system is now considered central to the regulation of feeding and metabolism.

 

Societal causes

While it may often be obvious why a certain individual gets fat, it is far more difficult to understand why the average weight of certain societies have recently been growing. While genetic causes are central to who is obese, they cannot explain why one culture grows fatter than another.

This is most notable in the United States. In the years from just after the Second World War until 1960 the average person's weight increased, but few were obese. In 1960 almost the entire population was well fed, but not overweight. In the two and a half decades since 1980 the growth in the rate of obesity has accelerated markedly and is increasingly becoming a public health concern.

There are a number of theories as to the cause of this change since 1980. Most believe it is a combination of various factors.

• Lack of activity: obese people appear to be less active in general than lean people, and not just because of their obesity. A controlled increase in calorie intake of lean people did not make them less active; correspondingly when obese people lost weight they did not become more active. Weight change does not affect activity levels, but the converse seems to be the case^[7].

• One of the most important is the much lower relative cost of foodstuffs: massive changes in agricultural policy in the United States and Europe have led to food prices for consumers being lower than at any point in history. Sugar and corn syrup, two huge sources of food energy, are some of the most subsidized products by the United States government. This can raise costs for consumers in some areas but greatly lower it in others. Current debates into trade policy highlight disagreements on the effects of subsidies.

• Increased marketing has also played a role. In the early 1980s the Reagan administration lifted most regulations pertaining to advertising to children. As a result, the number of commercials seen by the average child increased greatly, and a large proportion of these were for fast food and candy.

• Changes in the price of mineral oil and petrol are also believed to have had an effect, as unlike during the 1970s it is now affordable in the United States to drive everywhere — at a time when public transit goes underused. At the same time more areas have been built without sidewalks and parks.

• The changing workforce as each year a greater percent of the population spends their entire workday behind a desk or computer, seeing virtually no exercise. In the kitchen the microwave oven has seen sales of unhealthy frozen convenience foods skyrocket and has encouraged more elaborate snacking.

• A social cause that is believed by many to play a role is the increasing number of two income households where one parent no longer remains home to look after the house. This increases the number of restaurant and take-out meals.

• Urban sprawl may be a factor: obesity rates increase as urban sprawl increases, possibly due to less walking and less time for cooking^[8].

• Since 1980 both sit-in and fast food restaurants have seen dramatic growth in terms of the number of outlets and customers served. Low food costs, and intense competition for market share, led to increased portion sizes — for example, McDonalds french fries portions rose from 200 calories (840 kilojoules) in 1960 to over 600 calories (2,500 kJ) today.

• Increased food production is a likely factor. The U.S. produces three times more food than U.S. residents eat.

• Increasing affluence itself (including many of the above factors as accompaniments of affluence) may be a cause, or contributing factor since obesity tends to flourish as a disease of affluence in countries which are developing and becoming westernised [1]. This is supported by a dip in American GDP after 1990, the year of the Gulf War, followed by an exponential increase. U.S. obesity statistics followed the same pattern, offset by two years [2].

• An ageing population may also be a major factor, as the likelihood of becoming obese increases with age. Beyond their twenties, the older a person becomes the slower their metabolism becomes, reducing the amount of calories required to sustain the body, thus if a person does not reduce their intake of food with age, they will become obese over time. As the average age of individuals within a society increases, the rate of obesity also increases. This situation is exacerbated by the baby boom generation, which represents a disproportionately large portion of the population in many countries and is currently nearing the latter end of the typical lifespan in affluent nations, and therefore is in the high-risk zone for obesity.

Interestingly an increase in the number of Americans who exercise and diet occurred before the increase in obesity, and some scholars have even argued that these trends actually encouraged obesity. Nearly all diets fail, with participants resuming their previous eating habits or even engaging in binge eating. Many then see an overall increase in their weight. If the diet is then repeated and abandoned again, a pattern of rising and falling weight is established, known as weight cycling. Similarly those who work out but then stop can end up being heavier than those who never exercised.

 

Poverty link

Some obesity co-factors are resistant to the theory that the "epidemic" is a new phenomenon. In particular, a class co-factor consistently appears across many studies. Comparing net worth with BMI scores, a 2004 study^[9] found obese American subjects approximately half as wealthy as thin ones. When income differentials were factored out, the inequity persisted — thin subjects were inheriting more wealthy than fat ones. Another study finds women who married into higher status predictably thinner than women who married into lower status.

 

Complications

Obesity, especially central obesity (male-type or waist-predomimant obesity), is an important risk factor for the "metabolic syndrome" ("syndrome X"), the clustering of a number of diseases and risk factors that heavily predispose for cardiovascular disease. These are diabetes mellitus type 2, high blood pressure, high blood cholesterol, and triglyceride levels (combined hyperlipidemia). An inflammatory state is present, which — together with the above — has been implicated in the high prevalence of atherosclerosis (fatty lumps in the arterial wall), and a prothrombotic state may further worsen cardiovascular risk.

Apart from the metabolic syndrome, obesity is also correlated (in population studies) with a variety of other complications. For many of these complaints, it has not been clearly established to what extent they are caused directly by obesity itself, or have some other cause (such as limited exercise) that causes obesity as well. Most confidence in a direct cause is given to the mechanical complications in the following list, compiled by the American Medical Association for general physicians:

• Cardiovascular: congestive heart failure, enlarged heart and its associated arrhythmia and dizziness, cor pulmonale, varicose veins, and pulmonary embolism
• Endocrine: polycystic ovarian syndrome (PCOS), menstrual disorders, and infertility
• Gastrointestinal: gastroesophageal reflux disease (GERD), fatty liver disease, cholelithiasis (gallstones), hernia, and colorectal cancer
• Renal and genitourinary: urinary incontinence, glomerulopathy, hypogonadism (male), breast cancer (female), uterine cancer (female), stillbirth
• Integument (skin and appendages): stretch marks, acanthosis nigricans, lymphedema, cellulitis, carbuncles, intertrigo
• Musculoskeletal: hyperuricemia (which predisposes to gout), immobility, osteoarthritis, low back pain
• Neurologic: stroke, meralgia paresthetica, headache, carpal tunnel syndrome, dementia^[10]
• Respiratory: dyspnea, obstructive sleep apnea, hypoventilation syndrome, Pickwickian syndrome, asthma
• Psychological: Depression, low self esteem, body image disorder, social stigmatization

While being severely obese has many health ramifications, those who are somewhat overweight face little increased mortality or morbidity. Some studies suggest that the somewhat "overweight" tend to live longer than those at their "ideal" weight[3]. This may in part be attributable to lower mortality rates in diseases where death is either caused or contributed to by significant weight loss due to the greater risk of being underweight experienced by those in the ideal category. Osteoporosis is known to occur less in slightly overweight people.

 

Therapy

The mainstay of treatment for obesity is an energy-limited diet and increased exercise. Although adherence to this regimen can cure obesity, many patients are unable to make the required sacrifices. In fact there are no studies showing that an energy restricted diet can lead to long term weight loss. It appears that the homeostatic mechanisms regulating body weight are very robust, thus impeding weight loss when attempted using calorie restriction. Recent scientific research has cast some doubt over whether or not dieting actually improves health, with some studies indicating that dieting may in fact be more detrimental than remaining overweight ^[11]

In a clinical practice guideline by the American College of Physicians^[12], the following five recommendations are made:

1. People with a BMI of over 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
2. If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of side-effects and the unavailability of long-term safety and efficacy data.
3. Drug therapy may consist of sibutramine, orlistat, phentermine, diethylpropion, fluoxetine, and bupropion. Evidence is not sufficient to recommend sertraline, topiramate, or zonisamide.
4. In patients with BMI > 40 who fail to achieve their weight loss goals (with or without medication) and who develop obesity-related complications, referral for bariatric surgery may be indicated. The patient needs to be aware of the potential complications.
5. Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who perform these procedures frequently have fewer complications.

Much research focuses on new drugs to combat obesity, which is seen as the biggest health problem facing developed countries. Nutritionists and many doctors feel that these research