Monday, August 25, 2008

Health Misreporting

There's a new study that purports to tell us that fat people can be healthy:

The Obese Without Cardiometabolic Risk Factor Clustering and the Normal Weight With Cardiometabolic Risk Factor Clustering

Prevalence and Correlates of 2 Phenotypes Among the US Population (NHANES 1999-2004)

Rachel P. Wildman, PhD; Paul Muntner, PhD; Kristi Reynolds, PhD; Aileen P. McGinn, PhD; Swapnil Rajpathak, MD, DrPH; Judith Wylie-Rosett, EdD; MaryFran R. Sowers, PhD

Arch Intern Med. 2008;168(15):1617-1624.

Background The prevalence and correlates of obese individuals who are resistant to the development of the adiposity-associated cardiometabolic abnormalities and normal-weight individuals who display cardiometabolic risk factor clustering are not well known.

Methods The prevalence and correlates of combined body mass index (normal weight, <25.0; overweight, 25.0-29.9; and obese, ≥30.0 [calculated as weight in kilograms divided by height in meters squared]) and cardiometabolic groups (metabolically healthy, 0 or 1 cardiometabolic abnormalities; and metabolically abnormal, ≥2 cardiometabolic abnormalities) were assessed in a cross-sectional sample of 5440 participants of the National Health and Nutrition Examination Surveys 1999-2004. Cardiometabolic abnormalities included elevated blood pressure; elevated levels of triglycerides, fasting plasma glucose, and C-reactive protein; elevated homeostasis model assessment of insulin resistance value; and low high-density lipoprotein cholesterol level.

Results Among US adults 20 years and older, 23.5% (approximately 16.3 million adults) of normal-weight adults were metabolically abnormal, whereas 51.3% (approximately 35.9 million adults) of overweight adults and 31.7% (approximately 19.5 million adults) of obese adults were metabolically healthy. The independent correlates of clustering of cardiometabolic abnormalities among normal-weight individuals were older age, lower physical activity levels, and larger waist circumference. The independent correlates of 0 or 1 cardiometabolic abnormalities among overweight and obese individuals were younger age, non-Hispanic black race/ethnicity, higher physical activity levels, and smaller waist circumference.
According to the New York Times:
Stephen Blair, a co-author of the study and a professor at the Arnold School of Public Health at the University of South Carolina, said the lesson he took from the study was that instead of focusing only on weight loss, doctors should be talking to all patients about the value of physical activity, regardless of body size.

“Why is it such a stretch of the imagination,” he said, “to consider that someone overweight or obese might actually be healthy and fit?”
As is typical in such news stories, no one even bothers to mention the fact that body mass index (BMI) is a hopelessly inadequate measure of bodyfat in the first place. Seemingly skinny people can have high bodyfat because they are so lacking in muscle mass; and at the same time, building any muscle mass via exercise is a good way to fall into the "overweight" category of BMI regardless of your level of bodyfat. It's baffling to me that anyone like this would be counted as evidence that being "overweight" (a term that readers might associate with bodyfat) is healthy.

At a minimum, it ought to be clarified in such stories that having too much bodyfat is probably not a good idea, no matter what your weight.


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