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.

Definition 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:
  • Genetic predisposition
  • Energy-rich diet
  • Limited exercise
  • Underlying illness
  • An eating disorder such as binge eating disorder
  • Stressful mentality (debated)

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.)

Binge Eating Disorder are people who eat too much, often in binges. The reason they eat too much is that eating reduces anxiety. One can compare with substance abuse, the causes are very similar. An important additional factor is that the person lacks ability to recognize hunger and satisfaction. The ability to recognize hunger and satisfaction is something you learn as a child. If parents give their child food when the child is distressed because of other factors than hunger, then the children will associate hunger with other distresses also as an adult.


  • Obesity is correlated (in population studies) with an increased risk of:
  • Heart disease
  • Metabolic syndrome X
  • high blood pressure
  • diabetes mellitus (type II)
  • high blood cholesterol and triglyceride (combined hyperlipidemia)
  • Certain types of cancer

Mechanical complications:

  • osteoarthritis
  • Gastroesophageal Reflux Disease (GERD)
  • obstructive sleep apnea syndrome
  • Carpal tunnel syndrome
  • Asthma

While being greatly overweight has many health ramifications, those who are somewhat overweight face little increased mortality. In fact the somewhat overwieght 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.

Worldwide distribution of obesity

The United States has one of the highest obesity rates in the world and is the first nation to have people who are both impoverished and obese.

The obesity epidemic is also increasing in Europe, Asia, and throughout the Americas: as the Indian newspaper The Tribune states:

Obesity also plagues middle eastern countries, with 35 per cent of Egyptians considered obese, a greater proportion than the population in the USA at 20 per cent.

The spread of obesity is thought to be related to the increasing westernisation of these countries (see the China project), which brings fundamental change in eating habits and decreased levels of physical activity.

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