According to the latest study the fat around the belly is the chief culprit in the link between obesity and cardiovascular disease. This study raises the possibility that people can be overweight without significantly raising their heart risk, so long as they carry the extra fat in places other than their belly. In fact, a few extra pounds may even lower the risk of death from heart disease, researchers found.
Earlier studies have shown a possible protective effect of being overweight—a phenomenon that has been called the “obesity paradox.” But the new study suggests the issue isn't about the dangers of obesity, but rather the limitations of the tool called body mass index, or BMI, that is typically used to measure it.
This new report says obesity is clearly an important factor in heart risk. “Fat does matter,” says Francisco Lopez-Jimenez, a cardiologist at Mayo Clinic, Rochester, Minn., and senior author of the study. “But it depends on how you measure [it]. It's mostly about fat distribution and not total fatness.” The report was published online Monday by the Journal of the American College of Cardiology.
The researchers, for this study pooled data from nearly 16,000 patients with heart disease U.S., Denmark, France and Korea and found that the bigger the waistline, the higher the chances of dying in the months and years after a heart attack or major heart procedure. The heightened risk remained even for people considered normal weight according to the BMI measurement tool they find.
BMI is based on only the height and weight and is widely accepted as a way to measure obesity in a large population. But its failure to differentiate between body fat and muscle mass or to account for where fat is located are among reasons its value in sizing up an individual patient has been challenged in this study. When patients in the study were assessed on BMI alone, without factoring in waist measurements, those who were overweight or obese had a 16% to 25% lower risk of dying than people whose BMIs ranked them as normal weight. Patients were followed for a median period of 2.3 years after a heart attack or heart procedure.
On the other hand patients who had a larger waistline, as measured by either waist circumference or waist-to-hip ratio, had a higher risk of death. They were 1.7 times as likely to die during the follow-up period as those with normal waist measurements, the researchers said. Waist measurements of 40 inches or more for men and 35 inches or more for women are considered in the danger zone as are waist-hip ratios (waist measurement divided by hip measurement) of greater than 0.9 for men and 0.85 for women.
“Our data suggest waist circumference and hip-waist-ratio to be more reliable than body mass index in stratifying mortality risk in coronary artery disease patients,” Dr. Thais Coutinho, the study's lead author and a cardiology fellow at Mayo Clinic and her co-authors concluded. “These findings might have significant implications for clinical practice, because it is generally accepted that, if body mass index is normal, no further measures of obesity are necessary, and no lifestyle modifications to induce weight loss might be recommended.”
“Fat is not created equal and where fat is located makes a difference,” says Michael Lauer, director of cardiovascular sciences at the National Institutes of Health's National Heart, Lung and Blood Institute. “We don't want people to get the message that it's OK to be fat,” he says. Dr. Lauer was an independent observer. Visceral or intra-abdominal fat surrounding the internal organs has been found to be more metabolically active, producing more changes in cholesterol, blood pressure and blood sugar compared with people who have fat mostly in the legs and buttocks, the researchers said.
The study looked only at patients who had suffered a heart attack or had a major heart procedure. Several other large studies suggest belly fat is associated with higher risk of heart attack and other heart problems among people who haven't been diagnosed with heart disease.
In a study published in March in the Lancet by British researchers it was noted that BMI and abnormal waist measurements were similarly associated with risk of disease. But Salim Yusuf, executive director of the Population Health Research Institute at McMaster University in Hamilton, Ontario, says he thinks details in the British data were consistent with concerns about the impact of central obesity, the technical term for belly fat. He also noted that in patients without a history of heart problems, risks of obesity are reflected in conventional characteristics, such as blood pressure, elevated blood sugar and abnormal cholesterol.
“For a given BMI, there is a huge variation in waist circumference and that variation make a huge difference,” said Jean-Pierre Després, director of cardiology research and an obesity expert at institute universitaire de cardiologie et de pneumologie de Quebec in Quebec, Canada. He was author of an editorial accompanying the study. Genetics plays a “very strong” role in whether a person gains weight around the waist, Després says. He estimates that about 30 percent of the population has this tendency to put on fat in these “undesirable sites.”
The findings also underscore the importance of diet and especially physical exercise in combating belly fat. Research suggests that both aerobic exercises alone and in combination with resistance training has a beneficial effect on central obesity and overall heart risk.
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