Increased body fat percentage is associated with a higher risk of all-cause mortality, regardless of BMI, according to a study published in the Annals of Internal Medicine. In a second study, researchers found that young people who are not physically fit have an increased risk of developing type 2 diabetes later in life, regardless of body weight.

The first study, led by Raj Padwal, MD, MSc, included 49,476 women and 4,944 men aged ≥40 years who had been referred for bone mineral density testing. During a median of 6.7 years, 4,965 women died, and over a median of 4.5 years, 984 men died.

The researchers found that high body fat percentage and low BMI were associated with increased mortality in women and men.

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“Body mass index is widely used as a proxy for adiposity even though it more closely reflects lean mass than fat mass,” the researchers wrote. “Increasing BMI may therefore reflect higher fitness levels, greater metabolic reserve, and less cachexia — factors that are associated with greater survival — rather than increasing fat.”

The second study, led by Casey Crump, MD, PhD, included 1,534,425 male military conscripts from 1969 to 1997 with no prior diagnosis of type 2 diabetes. Every participant was aged 18 years at the time of the examination. Aerobic capacity was measured in watts, and muscle strength was measured in newtons per kilogram of body weight.

During 39.4 million person-years of follow-up, 34,008 participants (2.2%) were diagnosed with type 2 diabetes. Both low aerobic capacity and muscle strength were independently associated with an increased risk of developing type 2 diabetes. After 20 years of follow-up, the absolute difference in cumulative incidence of type 2 diabetes between the lowest and highest tertiles of aerobic capacity and muscle strength was 0.22%; this increased to 0.76% at 30 years and 3.97% at 40 years. The combination of low aerobic capacity and low muscle strength had the highest associated risk for type 2 diabetes (hazard ratio 3.07), even among participants with a normal BMI.