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Is Being A Little Overweight Really OK? The BMI Controversy

Resolving the recent controversy over BMI measurements

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Updated May 23, 2014

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Is being somewhat overweight - having a moderately elevated BMI - associated with increased medical risk, or is it not? While obesity pretty clearly increases medical risk, and while society and the medical experts have lately placed great emphasis on maintaining a "normal" body weight, the excess risk posed by being merely overweight (as opposed to obese) is less clear.

The unsettled nature of this question briefly popped into view a few years ago when an article appearing in the Lancet suggested that heart patients who were a "little" overweight, according to their BMI (body mass index) score, actually had a slightly lower risk than patients who were of "normal" weight. Even the authors of this paper seemed a little embarrassed by these findings. And to confuse the issue further, two major articles appearing at about the same time in the New England Journal of Medicine supported the more popular notion - that being overweight, by any amount, increases the risk of mortality.

Trying to stifle public confusion about the matter, according to the Wall Street Journal the Centers for Disease Control instructed its researchers not to comment publicly on the new studies, and " a spokeswoman for the agency had no comment as well." ( You can read the Wall Street Journal article here, but it requires a subscription.)

The BMI score is meant to be a quick way of determining whether a person has too much body fat. BMI scores of 20 to 24.9 are considered normal, scores of 25 to 29.9 are overweight, scores of 30 to 34.9 are obese, and scores above 35 are extremely obese. Scores under 20 are considered underweight. ( You can read about the BMI score, and easily calculate your own BMI, here.)

Virtually all studies using BMI scores agree on a few points. First, patients who are obese or extremely obese have a greatly increased risk of cardiovascular disease and death. Second, patients who are underweight also have an increased risk of death. (This is thought to be mainly because of underlying disease processes - such as heart disease, lung disease, cancer or infection -which themselves often produce weight loss as the disease progresses.)

If there is a controversy it centers around individuals who are classed as overweight, but not obese, that is, whose BMI scores are a bit over 25. Most studies have shown increased medical risk even for this mild state of overweight. But a few studies show a slightly lower risk for these individuals.

Several explanations for this apparent discrepancy have been suggested, but the one that has the most traction is the idea that the BMI measure itself - which simply takes into account one's weight and height - often gives a false measure of "overweight" if a person is simply in good shape and has good muscle mass. That is, for healthy individuals with BMIs of 25 or 26, the "excess" weight may actually not be fat.

A Comment:

Having too much fat - specifically, too much fat in the abdominal area - places significant metabolic stress on the cardiovascular system and increases the risk of cardiovascular disease. The BMI index is very accurate for individuals who are very underweight or very overweight (e.g., it is very difficult to put on enough muscle mass to get your BMI above 30 without abusing steroids), but BMI is less accurate for detecting individuals who are merely "overweight." There are, indeed, some individuals who have BMI scores in the 25 - 27 range just because they are in good shape. But, I submit, those individuals ought to know who they are.

So, if you have a BMI score in the "overweight" category, and are considering celebrating because you choose to believe the Lancet article and to ignore all the other evidence to the contrary, let's just have you answer this one question before you crack open that next Bud: Is your waist size less than than your hip size? If "yes," then you are probably one of those people in excellent physical shape, and the "excess" weight contributing to your BMI score is muscle, and not fat (in which case you were also not actually preparing to celebrate by consuming empty calories). But if the answer is "no," and you have that dreaded centrally-deposited fat, you have nothing to celebrate about.

For, while the BMI score is sometimes useful and easy to measure, the waist-to-hip ratio is probably the far more important index of cardiovascular risk.

Sources:

Romero-Corral A, Montori VM, Somers VK, et al. Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: A systematic review of cohort studies. Lancet 2006; 368: 666-678.

Adams KF, Schatzkin A, Harris TB, et al. Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. N Engl J Med 2006; 355:763-778.

Lee SH, Sull JW, Park J et al. Body-mass index and mortality in Korean men and women. N Engl J Med 2006; 355:779-787.

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