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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.
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:
- Genetic predisposition
- Energy-rich diet
- Limited exercise
- Underlying illness
- 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.)
Complications
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 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.
Therapy
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 (XenicalŽ,
reduced intestinal fat absorption by inhibiting pancreatic lipase) and sibutramine (ReductilŽ, MedariaŽ, an anorectic).
In the presence of diabetes mellitus, there is evidence that
the anti-diabetic drug metformin (GlucophageŽ) 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.
Controversies
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]
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.
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. -- [2]
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. There is some
speculation that some food industries may be delaying attempts to limit the spread of obesity, see the ABC news article . The United states response[3] in November 2003 to the WHO draft strategy on
obesity introduced the notion of food industry-sponsored initiatives. These sorts of links with vested interests are regarded
with scepticism by some nutritionists[4] .
See also
External links
References
- Janssen I, Katzmarzyk PT, Ross R. Waist circumference and not body mass index explains obesity-related health risk.
Am J Clin Nutr. 2004 Mar;79(3):379-84.
- Roberts, S. B., Savage, J., Coward, W. A., Chew, B., & Lucas, A. (1988). Energy expenditure and intake in infants born to
lean and overweight mothers. The New England Journal of Medicine, 318, 461-466.
- Ross, J. G., & Pate, R. R. (1987). The National Children and Youth Fitness Study II: A summary of findings. Journal of
Physical Education, Recreation and Dance, 58(9), 51-56. EJ 364 411.
- Wolf, M. C., Cohen, K. R., & Rosenfeld, J. G. (1985). School-based interventions for obesity: Current approaches and
future prospects. Psychology in the Schools, 22, 187-200. EJ 318 072.
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