Obesity

(Date of publication 19 November 2004)

Some 300 million people around the world are obese and most suffer from weight-related illnesses, according to leading specialists at the recent meeting of the International Association for the Study of Obesity, who concluded that the global obesity epidemic is completely out of control. In South Africa more than 30% of men and 50% of women are overweight, obesity in Japanese men has risen by 100% since 1982, and huge numbers of overweight children in the Middle East are developing diabetes. The knock-on effects are enormous and sometimes surprising. For example, health costs arising from excess weight account for 9.1% of total US medical expenditure ($78.5 billion), and because the average weight of Americans rose by 10 lbs (4.5 kg) during the 1990s, US airlines burned 350 million more gallons of fuel in 2000 than in 1990, releasing an extra 3.8 million tons of CO₂ into the atmosphere.

Obesity is usually defined as a Body Mass Index (BMI) of 30 or above. Your BMI can be calculated by dividing your weight in kilograms by the square of your height in metres - or by utilising the handy reckoner here, which also allows you to enter imperial measures.

The greatest numbers of obese people are found in the USA. This CDC map for 2003 shows that in four states more than 25% of the population were obese, and in most of the rest the figure was between 20% and 24%. Contrast this with 1991, when no state had a prevalence rate above 19% and only four had rates above 15%. Statistics for the UK are just as alarming; the incidence in adults has tripled since 1982 and today 19% of Britons are obese, with 39% being overweight. In England alone, obesity is responsible for 30,000 deaths each year.

The basic cause of obesity is expending less energy than is consumed in the form of food. However, the regulation of weight is incompletely understood and a number of factors are believed to be involved in the accumulation of excessive body fat. Genes may have an influence; for example, mutations in the ob gene may interfere with the production of leptin, which acts on areas of the brain that control metabolism, and studies have shown that the heritability of BMI is about 33%. The personal environment has an even greater effect. Growing up with a low socioeconomic status is a powerful risk factor for obesity, as are a large food intake and a sedentary lifestyle, which may paradoxically increase food intake in some people. Regulatory determinants that may predispose to weight gain include pregnancy, a fat childhood, drug treatment with steroids or psychoactive drugs, and psychological factors.

Obesity is associated with a wide range of severe complications. The chart near the top of this page illustrates how the risk of developing Type 2 diabetes mellitus and hypertension is directly proportional to the BMI. The lower chart shows that women with a BMI of 35 or over have more than 93 times the risk of developing Type 2 diabetes than women whose BMI is less than 22. However, the distribution of fat is also important, the incidence of co-morbidity being higher when fat is concentrated around the waist rather than on the hips and thighs. In general, a waist-to-hip circumference ratio of more than 0.9 for men and 1.0 for women is associated with an increased risk of morbidity.

The specific health risks related to obesity are covered more extensively on the WebPath and Weight.com sites, the latter having links to further details about each condition mentioned. In particular, the incidence of Type 2 diabetes in the USA increased by 25% between 1990 and 2000, and 80% to 90% of these patients are obese. Research at Harvard University indicates that excess weight stresses the endoplasmic reticulum in individual cells, so that they suppress insulin receptors on the cell surface, leading to insulin resistance and Type 2 diabetes. If you are especially interested in this condition, there is a clinical review at the emedicine.com site.

Another major consequence of obesity is its adverse effect on cardiovascular health. Population studies suggest that it is directly responsible for at least 75% of cases of hypertension. Excessive weight also raises plasma triglyceride and low density lipoprotein ('bad cholesterol') levels, multiplies the risk of stroke, and is associated with a 12-fold increase in mortality in 25 - 35 year olds.

Lifestyle changes - such as adopting a more sensible diet and increasing physical activity - can reduce weight effectively, particularly if the BMI is between 27 and 30, when it can produce moderate weight loss with minimal side effects. However, if this approach fails or the condition is severe (BMI>40), surgery may be considered. The three main procedures are outlined here. In vertical gastric banding, the stomach is stapled to reduce its capacity, while lasparoscopic gastric banding is a minimally invasive method in which a band is placed around the upper portion of the stomach to achieve the same effect. The Roux-en-Y gastric bypass combines stapling of the upper stomach with the attachment of the distal small intestine to the stomach pouch thus created. Information about risks, benefits, success rates, complications and side effects are available from the American Obesity Association.

Having focused on the dire consequences of obesity, it is pleasing to note that there are numerous examples on the Web of people triumphing over the condition and regaining normal weight, complete with documentary evidence. Would you believe that this photographand this one are the same person before and after treatment?

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A Tour around Obesity

A Tour around Obesity