Researchers investigating links between mortality, BMI, and body fat percentage have concluded that low BMI and high body fat are associated with increased risk for all-cause mortality
Results from previous population-based cohort studies of middle-aged and older adults, and more focused studies in people with chronic diseases such as heart failure and chronic kidney disease, have reported lower mortality rates in overweight and mildly or moderately obese people than in those with normal weight. This “obesity paradox” led researchers to hypothesize that greater body fat percentage might be independently associated with increased mortality because BMI is an imperfect measure of body fat.
“When BMI and body fat percentage were included in the same fully adjusted models, low BMI and high body fat percentage were both associated with increased all-cause mortality,” the researchers wrote in the Annals of Internal Medicine. “Mortality increased as BMI decreased and body fat percentage increased. This suggests that after adjustment for BMI, higher adiposity may have a detrimental effect on survival and that after adjustment for body fat percentage, a lower BMI.”
Researchers performed a population-based cohort study of 49 476 women and 4944 men in Manitoba, Canada. Participants were 40 years or older and had initial dual-energy x-ray absorptiometry of the spine and hip for bone mineral density testing between 1999 and 2013. They followed participants until death or the end of the study.
For women, mean age was 63.5 years, mean BMI was 27.0 kg/m2, and mean body fat percentage was 32.1%. Mean age for men was 65.5 years, mean BMI was 27.4 kg/m2, and mean body fat percentage was 29.5%.
The Pearson correlation between BMI and mean body fat percentage was 0.76 in women and 0.63 in men.
In the fully adjusted models, low BMI in women was significantly associated with increased mortality for women in the 2 lowest quintiles (hazard ratios [HRs]=1.44 [95% CI, 1.30-1.59] and 1.12 [95% CI, 1.02-1.23] for quintiles 1 and 2, respectively). Body fat percentage was also independently associated with significantly higher mortality for women in the highest quintile (HR=1.19; 95% CI, 1.08-1.3).
Researchers observed similar results among men, noting an increase in mortality among the lowest BMI quintile (HR=1.45; 95% CI, 1.17-1.79) and highest body fat percentage quintile (HR=1.59; 95% CI, 1.28-1.96).