Researchers at the Mayo Clinic in Minnesota recently reviewed 40 studies comprising over 250,000 heart patients; average follow-up time was just under four years. Their conclusion? The Body-Mass Index (BMI) is not useful in predicting mortality in patients with coronary artery disease (CAD). More to the point, fatter people with CAD don’t die at higher rates than leaner ones, with the exception of morbidly obese people, whose relative risk of death from cardiac events was 1.88 times the norm of patients studied.
The findings were published in this week’s issue of The Lancet, which, if you’ve never heard of it, is the British answer to the New England Journal of Medicine in terms of prestige and overall reputation. You can read the summary here, but you have to register (it’s free) at the Lancet site first.
The researchers, who emphasized that obesity and overweight are still grave risk factors for various medical problems, concluded that the reason the BMI fails to correlate well with outcomes in this population is that it fails to discriminate between lean body mass (i.e., muscle) and blubber.
The researchers know a lot more than I do, and I haven’t read the whole study, but I admit to a bit of skepticism here. Most people with high BMIs — in fact, most people, period — are not heavily muscled. Patients with CAD and high BMIs are even less likely than younger, healthy people to be built like linebackers. I’d be willing to bet that close to 100% of the high-BMI patients studied by the Mayo team were, or are, simply fat. And if I had to wager a guess — and if Orac or one of the other medical types reads this, maybe he or she can jump in — I would further speculate that the higher mortality in low-BMI CAD patients was tied to factors such as the wasting that occurs in late-stage congestive heart failure and other co-morbidities. But the study summary notes that the team, not surprisingly (the Mayo isn’t generally associated with amateur hour), controlled for confounding factors.
Naturally, Big Fat Blog is pleased to report these findings, but as usual muddles some important details. Paul McAleer correctly notes that the Reuters article to which he links gives an annual-deaths-from-obesity-figure — 300,000 – that the Centers for Disease Control (CDC) lowered to 112,000 over a year ago. But his claim that “the BMI is useless as used today to gauge one’s health” is overreaching and is certainly not supported by the findings of the Mayo group, which looked only at heart patients. Apparently some folks have forgotten that people become ill and die from numerous health problems experienced at far higher rates in obese and overweight persons than in leanfolk.
That said, were I fat, inclined toward righteousness, and not all that inclined to dig below the surface, I too would be wondering why the researchers were so adamant about insisting that excess weight is pestilential when their own study suggested just the opposite, at least with respect to one organ system; that the researchers could only speculate about the reason(s) for their findings makes their claims about blotation seem all the more shaky.