A recent meta- analysis in JAMA by Flegal et al has created a major media frenzy and angry reactions in the public health research community by concluding: “Relative to normal weight, both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality.”
At a time when childhood underweight has been downgraded from #1 global risk factor in 1990 to #8 in 2010, while high body mass index (BMI) rose from #10 to #6 (Lancet. 2012 Dec 15;380(9859):2224-60. doi: 10.1016/S0140-6736(12)61766-8.) it is counterintuitive to learn from Men’s Health that fat guys live longer. Did the media misinterpret the JAMA study, or is Dr. Walter Willett (Harvard School of Public Health, Chair, Nutrition Department) right : “Stated politely, the paper is a pile of rubbish” and “It is clear that the Flegal study is misleading and should be ignored by health professionals and the general public. ”
The Harvard School of Public health has staged a symposium on Feb. 20 (check out the videocast), asking “Does being overweight really reduce mortality?” The participants squash the JAMA study. Main arguments: The low BMI groups are biased by the sick and smokers, and high quality studies containing data from 6 million individuals were excluded.
Irrespective of potential weaknesses of the JAMA study: Its data, as well as previous studies, suggest that the nadir of the J-shaped BMI vs. mortality curve is farther to the right than most people think, close to a BMI of 25. Of note, no data exists to demonstrate that a dietary intervention to bring BMI to the nadir (fasting, or ‘overeating’, depending from which side of the curve you come) reduces individual mortality!