BMI may not provide an accurate picture of a person's health

Jun 9 2009

Being overweight is a health concern, and using only body mass index (BMI) to determine weight classification may not give an accurate picture of a person's health, according to an advisory published in Circulation: Journal of the American Heart Association.

About one-third of the U.S. population is overweight - the middle range between normal weight and obesity. Overweight in adults is a BMI of 25.0 to 29.9. BMI is a numerical value of weight in relation to height.

Studies that examined the relationship between overweight (as measured by BMI) and risk of death from all causes (often referred to as total mortality) have had contradictory results. However, considering death from all causes overlooks the role that overweight may play in the development of risk factors for cardiovascular diseases.

Even among the young, overweight is related to the development of serious risk factors for cardiovascular disease, such as high blood pressure, obesity, elevated levels of cholesterol and type 2 diabetes.

Part of the problem with quantifying the true impact of overweight lies in the way it's commonly measured, say the experts. The widely-used body mass index doesn't distinguish between fat mass which is related to important health concerns - such as type 2 diabetes - and lean mass, including muscle, which reduces health risks. Also, BMI does not directly measure the distribution of fat, such as whether there is greater fat at the waist than at the hips, which may be more detrimental to health.

Focusing on the relationship between total mortality and BMI misses the "larger picture," the statement said.

"This larger picture includes important relationships between BMI and other health outcomes, such as cardiovascular disease and its risk factors," said Cora E. Lewis, M.D., M.S.P.H., lead author of the advisory and professor of medicine and public health at the University of Alabama at Birmingham. "Arguably, the most important relationship among the cardiovascular disease risk factors is diabetes, which is significantly more common in overweight than in normal-weight people."

The advisory recommends doing research on overweight and health, beyond studies that focus solely on the relationship between total body mass index and risk of death.

"Meanwhile, we cannot afford to wait for this research to begin addressing the problem of overweight in our patients and in our society," write the advisory authors.

An increasing number of children are overweight, which puts them at risk for developing higher than normal blood pressure, blood cholesterol and blood sugar.

"Weight gain is progressive and weight loss difficult. Although a young child is unlikely to have a heart attack, overweight children are likely to become overweight or obese adults, which puts them at risk for cardiovascular events as they mature. Achieving and maintaining a healthy body weight is of high importance for all Americans," said Lewis.

Physical inactivity and excess weight increase risk of death and other adverse health outcomes; so overweight and obese persons in particular would benefit from adopting a physically active lifestyle and healthy eating habits.

Advisory co-authors include Kathleen M. McTigue, M.D., M.P.H.; Lora E. Burke, Ph.D., M.P.H.; Paul Poirier, M.D., Ph.D.; Robert H. Eckel, M.D.; Barbara V. Howard, Ph.D.; David B. Allison, Ph.D.; Shiriki Kumanyika, Ph.D., M.P.H.; and F. Xavier Pi-Sunyer, M.D. Author disclosures are available on the manuscript.

For tips on eating well and losing weight, visit americanheart.org/weightloss.