The secrets of longevity are as diverse as the people who live long enough to be invited to reveal them. The science of life expectancy, however, includes a universal premise. All things being equal, shedding excess weight reduces the risk of premature death from related illnesses such as heart disease, hypertension and diabetes. Now a new study raises doubts whether this is true of people who are overweight, as opposed to obese. The real surprise is that scientists do not know why.
Analysis of 97 studies involving 3 million men and women worldwide, including Americans, Chinese and Europeans, found, as expected, higher mortality among the significantly obese. But it also found that people who were merely overweight died at slightly lower rates than those of so-called normal weight. Epidemiologist Katherine Flegal, lead author of findings published in the Journal of the American Medical Association, noted that this had been observed before. Other studies suggest that overweight or mildly obese people are treated more aggressively by their doctors for high blood pressure or cholesterol. Moderately overweight people may also be more likely to see the need for exercise, and thin people may not have controlled their weight by healthy means.
None of this suggests that carrying a few extra kilos actually makes someone healthier. As we bring waistlines back under control after the festive season, we should reflect on a recent study by the University of Hong Kong medical faculty that found waistlines, or "central obesity", were the most accurate pointer to the disturbing incidence of non-alcoholic fatty liver disease, a precursor to liver cancer or cirrhosis. And obesity among our schoolchildren last year was still significantly higher than 15 years ago, though it is now trending downwards.
Amid the fast-food culture and sedate lifestyle of our affluent society, it does suggest that other lifestyle factors such as exercise and moderation, including a healthy diet and work-life balance, can also bear on life expectancy.