Overweight and mortality: surprising new data

As concern about the health implications of the obesity epidemic has increased one frequently mentioned claim is that the current generation will be the first to live shorter lives than their parents. The assumption is that the effects of obesity on the risk for chronic disease are so significant that life expectancy will inevitably fall. But new evidence suggests that this assumption may be wrong.

New meta-analysis

A new meta-analysis of the effects of overweight and obesity on all-cause mortality was published this month in the Journal of the American Medical Association. The analysis included data from 97 studies from around the world, providing a combined sample size of more than 2.88 million subjects and more than 270,000 deaths.

The risk of death of all obese subjects (BMI>30) was substantially and significantly higher (18%) than that of subjects of normal weight (BMI 18.5-25) – the sort of finding that we have come to expect. However, the results told a different and perplexing story when narrower weight categories were considered. For example, those who were overweight (BMI 25-30) experienced 6 per cent lower risk of mortality than subjects of normal weight. Subjects with grade 1 obesity (BMI 30-35) had the same mortality risk as subjects of normal weight. Consequently, the mortality risk associated with obesity appeared to be due entirely to higher grades of obesity – BMI greater than 35, which was associated with a 29% increase in risk.

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