Body Mass Index found useless because it does not consider body composition

New research published in The Lancet medical journal suggests that the Body Mass Index (BMI) system of classifying body weight may be inaccurate for assessing the risk of dying prematurely from heart disease.

The BMI, which classifies people as "underweight," "normal weight," "overweight" or "obese," is calculated by dividing a person's weight by their height squared. However, researchers say that because the BMI does not take into account body composition -- whether or not excess weight is fat or muscle -- it is not an accurate measure of predicting early death for heart patients.

Researchers from the Mayo Clinic in Rochester, Minn., examined data from 40 studies involving 250,000 people with heart disease, and found that patients identified as "overweight" according to BMI standards survived longer than "normal" weight patients. The researchers believe that because muscle weighs more than fat, many physically fit people are classified as "overweight," when in reality they are less likely to die young than a "normal" weight individual whose excess weight is mostly fat.

The study's lead researcher, Dr. Francisco Lopez-Jimenez, says the study's aim was not to prove that obesity isn't harmful, but that measuring risk of heart disease should come from BMI combined with other body composition measures, such as waist-to-hip ratio, which calculates the amount of abdominal fat. Such fat -- called visceral fat -- packs in around the organs in the abdomen and releases acids that increase the risk of heart disease, high blood pressure and high blood sugar.

"When assessing the risk of developing coronary heart disease, or dying from it, what really matters is how much fat you are carrying in your abdomen. BMI is related to, but is not, an absolute measurement of abdominal fat," says Judy O'Sullivan, a spokeperson for the British Heart Foundation. "The most important thing to consider is your body shape and weight. Eating less and being more active is an effective way of controlling both and improving your heart health."