Leo Sher, M.D.

Overweight and obesity have become a major public health problem in both developing and developed countries as they are related to a wide spectrum of diseases including diabetes, cardiovascular diseases, cancer and depression.

Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in meters (kg/m²). The current value settings are as follows: a BMI of 18.5 to 25 may indicate optimal weight; a BMI lower than 18.5 suggests the person is underweight while a number above 25 may indicate the person is overweight; a BMI below 17.5 may indicate the person has anorexia nervosa or a related disorder; a number above 30 suggests the person is obese; and a number above 40 suggests the individual is morbidly obese. In adults, BMI correlates strongly with the total body fat content. Because muscle weighs more than fat, people who are unusually muscular may have a high BMI.

BMI has been used by the World Health Organization as the standard for recording obesity statistics since the early 1980s. The U.S. National Institutes of Health (NIH) now defines normal weight, overweight, and obesity according to the BMI rather than the traditional height/weight charts.

Many studies have shown that higher BMI is associated with higher mortality (1). A systematic review of 8 studies found that increased BMI is independently associated with increased risk of dementia (2). According to the NIH Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, adults who have a BMI of 25 or more are considered at risk for premature death and disability as a consequence of overweight and obesity (3). These health risks increase even more as the severity of an individual’s obesity increases.

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References:

1. Carlsson S, Andersson T, de Faire U, Lichtenstein P, Michaëlsson K, Ahlbom A. Body Mass Index and mortality: Is the association explained by genetic factors? Epidemiology, in press.

2. Gorospe EC, Dave JK. The risk of dementia with increased body mass index. Age Ageing 2007;36(1):23-9.

3. National Institutes of Health. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults.