Fatness, Fitness, and Health

Human Biology, 5th ed. (pp. 346-34) has a Current Issue feature on the topic of whether or not being “overweight” (BMI 25-30) is overstated as a risk factor for poor health or mortality. A report out just last week in The Archives of Internal Medicine (168: 1617-1624, 2008) supports that notion. The study documents the prevalence of six cardiometabolic risk factors (elevated blood pressure; elevated triglyceride level; decreased HDL level; elevated fasting glucose level; insulin resistance; systemic inflammation) in normal, overweight, and obese individuals. The study found that nearly 24% of all normal-weight individuals were ”metabolically abnormal” by virtue of having at least two of the six risk factors. And conversely, 54% of the overweight individuals were still metabolically healthy. The study suggests that just being overweight does not necessarily mean that an individual is at increased risk for heart disease.

A study published last December tends to support the hypothesis that being overweight is not as important a factor previously thought (Journal of the American Medical Association 298:2507-2516, December 5, 2007). In this study, 2603 adults over the age of 60 were tested for cardiovascular fitness (gentle treadmill test) and then mortality was followed for 12 years. Overweight individuals did have a higher mortality rate than did normal-weight individuals (18 vs 13 deaths per 1000 person-years). However, even more striking was the effect of fitness; mortality rate of the least-fit quintile was four times that of the most fit quintile (33 vs. 8 deaths per 1000 person-years.) Among the older generation at least, maintaining cardiorespiratory fitness may be more important than maintaining a normal body weight. Whether this is also true for younger individuals remains to be seen.