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Increasing body fat, not BMI, a primary risk factor for death

Keeping body fat low as you age is more important than achieving a low number on the scale, according to an article published in Annals of Internal Medicine. Both low body mass index (BMI), a measure of a person’s weight in relation to height, and high body fat percentage are independently associated with increased risk for death.

Recent studies have shown an association between mild obesity (as measured by BMI) and lower mortality risk. Known as the “obesity paradox,” these findings have been the source of debate, as physicians are advised to counsel obese patients to lose weight to decrease their risk for chronic conditions, such as diabetes and heart disease.

Because BMI is an imperfect measure of body fat, researchers hypothesized that greater body fat percentage, independent of BMI, would be associated with increased mortality.

They measured body fat using dual-energy x-ray absorptiometry (DXA) and BMI for 50,000 men and women over the age of 40 to examine associations between BMI and percent fat – alone and in combination – with mortality. They found that having a higher percent body fat was independently associated with reduced survival, as was having a low BMI.

These finding suggest that body composition, not just weight, needs to be considered when assessing a patient’s health and risk of death. The authors say that in some people, higher BMI may actually reflect non-fat tissue such as muscle.