12 January - 20 June 2016

Modest weight gain may be good for you

9 Jan 13

The world's media also picked up a review paper in the Journal of American Medical Association, of reported hazard ratios (HRs) of all cause mortality for overweight and obesity relative to normal weight in the general population.  Key to understanding the study is to recognise the terminology used; underweight (BMI of <18.5), normal weight (BMI of 18.5-<25), overweight (BMI of 25-<30), and obesity (BMI of <30). Grade 1 obesity was defined as a BMI of 30 to < 35; grade 2 obesity, a BMI of 35 to < 40; and grade 3 obesity, a BMI of 40 or greater. The authors note that these standard categories have been increasingly used in published studies of BMI and mortality, but the literature reporting these results has not been systematically reviewed.  The 97 data sources used provided a sample size approaching 3 million people and more than 270,000 deaths.   The reviewers found that relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. However, grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.   The reviewers state that their findings are consistent with observations of lower mortality among overweight and moderately obese patients, although they acknowledge potential bias in the available data, and potential flaws in their own analysis. Nonetheless the large sample size does dilute bias from specific source data, and the authors suggest possible explanations for their findings, such as earlier presentation of heavier patients, greater likelihood of receiving optimal medical treatment, cardioprotective metabolic effects of increased body fat, and benefits of higher metabolic reserves.

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