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Low BMI, high body fat percentage associated with increased mortality

Recent findings published in Annals of Internal Medicine showed that low BMI and high body fat percentage were independently associated with increased mortality.

“These findings suggest that body composition, not just weight, needs to be considered when assessing a patient’s health and risk of death,” William D. Leslie, MD, MSc, professor of medicine and radiology at the University of Manitoba, Canada, told Healio Internal Medicine. “In some people, higher BMI may actually reflect nonfat tissue such as muscle, and this did not appear to be harmful in terms of survival.”

William D. Leslie

Previous population-based cohort studies of middle-aged patients with chronic diseases have reported lower mortality rates in patients who are overweight compared with patients who are normal weight, the researchers wrote. This unexpected finding was termed “the obesity paradox.” The researchers believe that this finding is due to BMI being used as a measure for body fat, which confounds the relationship between obesity and mortality risk.

To determine the associations of BMI and body fat percentage with all-cause mortality, the researchers performed a population-based cohort study of 49,476 women and 4,944 men who underwent dual-energy X-ray absorptiometry (DXA). The researchers constructed adjusted, sex-stratified Cox models and divided BMI and DXA-derived body fat percentage into five quintiles.

For women, the researchers found that a BMI of 22.52 kg/m² or less (HR = 1.44; 95% CI, 1.3-1.59) and a body fat percentage of more than 38.68% (HR = 1.19; 95% CI, 1.08-1.32) were associated with higher mortality. For men, the researchers found that a BMI of 23.85 kg/m² or lower (HR = 1.45; 95% CI, 1.17-1.79) and a body fat percentage higher than 36.14% (HR = 1.59; 95% CI, 1.28-1.96) were associated with higher mortality.

The results suggest that BMI may be an inappropriate measure for obesity, the researchers wrote.

“Patients and physicians need to be aware that weight and BMI are not always reliable indicators of a healthy body size,” Leslie said. “Having the ‘right stuff,’ (ie, muscle mass) and avoiding the ‘wrong stuff,’ (ie, excess fat mass) is probably optimal.” – by Will Offit

Disclosure: Leslie reports grants from Genzyme and Amgen and speaker fees from Amgen, Eli Lilly, and Novartis outside the submitted work.