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Can you be normal weight and fat at the same time?
That's the implication of a provocative recent report from the Mayo Clinic, which suggests that fat in your body can get you and your heart into trouble even if you don't look fat and if the scale tells you you're healthy.
The Mayo researchers, led by cardiologist Francisco Lopez-Jimenez, have coined a term for the phenomenon: normal weight obesity. In a study that looked at data from 6,171 Americans with normal body size, as measured by body mass index, those with a high percentage of body fat were at significantly greater risk of future heart problems than those with low amounts of fat. Their bodies 'behave like they are obese, but they are not,' Dr. Lopez-Jimenez says.
People don't have to be overweight to have excess body fat. Instead, these people have a higher ratio of fat to muscle tissue than do people with low body fat. Indeed, even people of the same weight, or those with comparable body mass index, which factors together weight and height, can have different body-fat percentages.
Based on results of the nine-year study, as well as U.S. Census and obesity data, Dr. Lopez-Jimenez and his colleagues estimate that as many as 30 million Americans may fall into the normal-weight-obesity category, many of them unaware they may be at increased heart risk.
The study 'drills down on a population where we're making assumptions that everybody is healthy. It may well be that they're not,' says Robert Eckel, an obesity and metabolic-syndrome expert at the University of Colorado, Denver, who wasn't involved with the study.
But Dr. Eckel and other medical experts caution that the findings need to be validated with additional research. Big epidemiological studies such as the Mayo report are useful for spotting important trends and raising hypotheses for further inquiry. But they are not necessarily reliable for prescribing specific remedies for individual patients.
Indeed, Dr. Eckel says he doesn't think the study's results mean people should have their body fat measured to assess their cardiac risk. Generally, a little extra weight around the middle among normal weight people should be a sufficient wakeup call, other doctors say. More research is needed to determine whether reducing body fat percentage in such people would lower risk of heart disease.
Among some of the Mayo Clinic study's findings: High body fat among normal-weight men and women was associated with a nearly four-fold increase in the risk for metabolic syndrome -- a cluster of abnormalities including elevated blood sugar and blood pressure. This syndrome is common among people who are obese and is an increasingly important precursor to diabetes and cardiovascular disease. For women, high body fat meant a heightened risk of being diagnosed with cardiovascular disease over the course of the study. Both men and women had a higher risk of abnormal cholesterol and men with high body fat were more likely to develop high blood pressure.
The research suggests that body mass index, or BMI, the tool doctors and researchers often use to determine whether a person is obese, may fall short in some cases as an indicator of good health. BMI is obtained by dividing your weight in kilograms by your height in meters squared. People with a BMI between 18.5 and 24.9 -- the range for the participants in the Mayo study -- are considered to be normal weight under government guidelines. A BMI of 30 or higher indicates obesity, while people in the range from 25 to 29.9 are considered overweight. The overweight category in particular has generated controversy because many people who exercise regularly and are considered fit have BMIs above 25. 2010-03-08
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