By Lisa Collier Cool
May 19, 2011

Did you know that a big belly is as dangerous to your health as smoking a pack of cigarettes daily or having high cholesterol? People with clogged arteries and a wide waistline are nearly twice as likely to die prematurely, even if their body mass index (BMI) is normal, according to a study published in the May 10 issue of Journal of the American College of Cardiology. One of the Mayo Clinic researchers’ most surprising findings was that as BMI went up, risk of death from CAD actually went down, thus confirming the so-called “obesity paradox” observed in some earlier studies.

Although obesity raises the risk of premature death from all causes, the impact of BMI on coronary artery disease (CAD) has been controversial since some studies report that increasing BMI seems to actually protect against CAD. Yet it doesn’t make scientific sense that obesity could be good for the heart. To investigate the apparent paradox, the Mayo Clinic researchers studied two other ways to measure body fat to see which method was the best predictor of CAD mortality. Here’s a closer look at the study which pooled data from six earlier studies involving 15,923 people.

What body fat measurements were studied? The study compared measures of overall obesity (BMI) and measures of central obesity (waist-to-hip ratio and waist circumference). CAD patients with central obesity (belly fat) were 70 percent more likely to die during the study period, which had an average of 2.3 years of follow-up.

How does BMI affect health risks? BMI is a measure of weight relative to height. You are considered normal if your BMI is 18.5 to 24.9, overweight if it’s 25 to 29.5, and obese if it’s 30 or above. In the study, 6,648 people had a normal BMI and 2,396 were obese. The 33 percent of CAD patients with the highest BMI had 36 percent lower risk of death in the study. Although BMI is widely used by doctors to screen for obesity, "it is not a good measure of body fatness and gives no insight into the distribution of fat,” said Thais Coutinho, MD, the study’s lead author in a statement. Also, BMI can produce misleading results in people who are very muscular.

What’s the impact of belly fat? Central obesity was measured by a composite of waist circumference and waist-to-hip ratio. CAD patients with large bellies were 70 percent more likely to die during the study period, even if their BMI was normal. Those who had both big bellies and a BMI above 30 were 93 percent more likely to die. “What seems to be important is how the fat is distributed on the body,” said Dr. Coutinho.

Why is belly fat so dangerous? Belly fat is more metabolically active than other types of fat, and is linked to harmful changes in cholesterol, blood pressure, and blood sugar—all of which are a boost for cardiovascular events, such as heart attacks, strokes, and death from CAD, while fat on the thighs or butt doesn’t influence these risks. This explains why people with a wide waist and apple shape are at increased risk for premature death, even if their BMI is normal, while those with an obese BMI and pear shape are at lower risk.

What’s the best way to check for belly fat? Measure your waist with a tape measure crossing your belly button and your hips at the widest point. A waist measurement above 35 inches in a woman or above 40 inches in a man indicates central obesity. Divide your waist measurement by your hip measurement--a ratio of .80 or less is healthy for women, while .90 is healthy for men. For both sexes, the danger zone that raises risk for heart disease and other serious disorders is a ratio of 1.0 or higher, even if your weight and BMI are normal.

What’s “normal-weight obesity”? Last year, the researchers reported that up to 30 million Americans may fall into the “normal-weight obesity” category, with many unaware that they’re at increased risk for heart disease and type 2 diabetes. These people have a normal weight, but their bodies behave as if they were obese, due to belly fat. If your waist circumference or waist-to-hip ratio are too high, slimming down could save your life. Shedding as little as five percent of your body weight (7.5 pounds for a 150 pound person) improves blood pressure and cholesterol and helps prevent diabetes and heart disease. You’ll also look and feel better.

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