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Obesity is a condition in which the natural energy reserve of a mammal (such as a human), which is stored in fat, is expanded far beyond usual levels to the point where it is believed to pose a health risk. Obesity in wild animals is relatively rare, but it is common in domestic animals like barrows and household pets who may be castrated, spayed, overfed and underexercised.

Table of contents
1 Definiton of obesity
2 Causes and effects of obesity
3 Therapy
4 Controversies
5 Viral origins?
6 See also
7 External links
8 References

Definiton of obesity

Obesity is a concept that is being continually redefined. In humans, the current measurement of obesity is the body mass index (BMI).

A person with a BMI over 25 kg/m2 is considered overweight; a BMI over 30 kg/m2 is considered obese. 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 BMI was created in the 19th century by the Belgian statistician Adolphe Quetelet, and remained largely intact until June 1998 when the BMI was revised downward. This had the remarkable effect of changing some people's status from "ideal" weight to "overweight" in one day!

The BMI has been subject to fundamental criticism, as it ignores fat distribution in the body (see central obesity), and the fat/muscle proportion in total body weight. This means that a very fit athete with little fat but highly developed, and therefore heavy, muscles could be classified as obese. For instance according to the BMI system Brad Pitt is overweight while Russell Crowe is obese. Many researchers therefore hold that a high "waist-hip ratio" is the best indicator of metabolic disturbance, as visceral fat is more prone to cause insulin resistance (Janssen I, et al. 2004.)

Causes and effects of obesity

Causative factors

Obesity is generally a result of a combination of factors:
Although there is no definitive explanation for the recent epidemic 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. Significant proportions (up to 30%) of the population in wealthy countries are now obese, and seen to be at risk of ill health (see e.g. Dr Joel Fuhrman.)

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 learnt in childhood. Learning theory suggests that early childhood conceptions may lead to an association between food and a calm mental state.

Societal causes

While it is often quite 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 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. Canada and Europe are somewhat behind the United States, with the rest of the world mixed. Some nations like Egypt and Mexico have also suffered from greatly increasing rates of obesity.

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

One of the most important is the much lower relative cost of foodstuffs, massive agricultural subsidies in the United States and Europe have lead to food prices for consumers being lower than at any point in history. Sugar and corn syrup, tow huge sources of calories are some of the most subsidized products by the United States government.

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 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 in the United States affordable to drive everywhere while public transit goes unused. 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 has seen sales of generally unhealthy frozen meals skyrocket and has encourage 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.

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 have lead to much large portions for the same price.

Interestingly the vast 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. Most diets fail, ending in binge eating and an overall increase in weight. Similarly those who workout but then stop can end up being fatter than those who never exercised.


Obesity is correlated (in population studies) with an increased risk of: While being greatly overweight has many health ramifications, those who are somewhat overweight face little increased mortality. In fact the somewhat overweight tend to live longer than the those at their "ideal" weight. Being overweight is a symptom of inactivity and a poor diet, both of which have important health impacts and changing diet and exercise levels, even if one's weight remains the same, provides many health benefits.


The mainstay of treatment for obesity is an energy-limited diet and increased exercise. Although adherence to this regimen can cure obesity, a large segment of patients is unable to make the required sacrifices. There might be an additional behavioral factor at the brain level "forbidding" obesity patients from losing too much weight.

Much research focusses on new drugs to combat obesity, which is seen as the biggest health problem facing developed countries. Some nutritionists feel that these these research funds would be better devoted to advice on good nutrition, healthy eating and promoting a more active lifestyle.

Medication prescribed for diet/exercise-resistant obesity is orlistat (Xenical®, reduced intestinal fat absorption by inhibiting pancreatic lipase) and sibutramine (Reductil®, Medaria®, an anorectic).

In the presence of diabetes mellitus, there is evidence that the anti-diabetic drug metformin (Glucophage®) can assist in weight loss - rather than sulfonylurea derivatives and insulin, which often lead to further weight gain. The thiazolidinediones (rosiglitazone or pioglitazone) can cause slight weight gain, but decrease the "pathologic" form of abdominal fat, and are therefore often used in obese diabetics.

Increasingly, surgery is being used to limit stomach capacity (and thus food intake); this can happen laparoscopically. Ileal bypass reduces the length of the intestine and hence absorbing surface, but has more complications.


There is continuous debate on what constitutes the ideal diet in the prevention and treatment of obesity, and much of the available scientific evidence is contradictory or statistically untenable.

A leading nutritionist (Professor Thomas Sanders, the director of the Nutrition, Food & Health Research Centre at King's College London) emphasises the need for balance between activity and consumption:

In trials, there is no evidence suggesting that reducing fat intake has an effect on obesity. As long as your expenditure equals what you eat, you won't put on weight, regardless of how high the fat content is in your diet (The Times, London, 10/3/04).

Controversy also exists as to whether the concept of "obesity" is a valid one. These critics assert that physically active people are healthier than the sedentary regardless of their body weight. The focus on weight and body mass is fed, in their view, by a diet promotion industry, drug companies, and segments of the medical profession for profit purposes, by promoting a vision that equates health with slenderness, and makes extreme slenderness of a sort that is quite difficult for most people to achieve an ideal. In The Obesity Myth, Paul Campos writes that:

. . . (F)rom the perspective of a profit-maximising medical and pharmaceutical industry, the ideal disease would be one that never killed those who suffered from it, that could not be treated effectively, and that doctors and their patients would nevertheless insist on treating anyway. Luckily for it, the American health care industry has discovered (or rather invented) just such a disease. It is called "obesity". Basically, obesity research in America is funded by the diet and drug industry - that is, the economic actors who have the most to gain from the conclusion that being fat is a disease that requires aggressive treatment. Many researchers have direct financial relationships with the companies whose products they are evaluating. [1]

On July 16, 2004, the US Department of Health and Human Services officially classified obesity as a disease. Speaking to a Senate committee, Tommy Thompson, the Secretary of Health and Human Services, stated that Medicare would cover obesity-related health problems. However, reimbursement would not be given if a treatment was not proven to be effective.

Viral origins?

Recent research has suggested that some human obesity may be caused by a viral infection. The virus AD-36 has been identified as a cause of obesity in animals.

See also

External links