A new study questions the use of body mass index (BMI) to predict the effect of obesity on health, saying it ignores important health factors such as how fat is distributed, the ratio of muscle to fat and differences in body composition. The authors call for more accurate and easy-to-use risk assessments.

BMI is a measure of weight in relation to height. According to the American Heart Association, a BMI of less than 25 indicates healthy weight; between 25 and 29.9, overweight; and 30 or higher, obesity.  You can determine your BMI using the American Heart Association’s BMI Calculator.

Research has shown higher risk of cardiovascular diseases, Type 2 diabetes and cancer for people with a BMI of 30 or higher. This study discusses the use of BMI in light of the “obesity paradox,” that obesity appears to protect some people against certain diseases.

“BMI is at best a crude biomarker that cannot independently predict risk,” said Robert Eckel, M.D. past president of the American Heart Association. “However, a large majority of people with a BMI of over 30 have at least one risk factor for cardiovascular disease other than age. Even more people with a BMI of over 40 have cardiovascular risk factors.”

Lifestyle factors or genetics can both contribute to metabolic health, even in people who are overweight or obese, but this is the exception rather than rule, he said.

Weight is one of the American Heart Association’s Life’s Simple 7 — seven health factors contributing to heart health and cardiovascular disease risk.