Abdominal fat raises heart disease risk

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OTTAWA: First came BMI. Now comes hypertriglyceridemic waist -- a cheap and simple way to identify people at increased risk of heart attack due to excess abdominal fat, even if they do not look obese.

In a study published this week in the Canadian Medical Association Journal, researchers from Quebec City's Laval University are reporting that a large waistline and high triglycerides -- a type of blood fat -- substantially increase the risk of coronary artery disease in both men and women.

Obesity has long been linked with a litany of health problems, but not every obese person has the same "metabolic abnormalities" associated with excess body fat, according to the research team -- a collaboration between investigators from Laval and scientists from the Netherlands and the U.K.

When it comes to diabetes and cardiovascular disease, what matters most is abdominal fat. Abdominal, or "visceral" fat, is a deep layer of fat that wraps around internal organs, distinct from the subcutaneous fat just beneath the skin that you can pinch with your fingers.

"In some people, the abdominal cavity is loaded with this visceral fat. But very obese patients could have a lot of total body fat without necessarily being abdominally obese," says Jean-Pierre Despres, director of research in cardiology at the Quebec Heart and Lung Institute and professor in the faculty of medicine at Laval.

Even waist circumference alone doesn't tell the entire story, because it doesn't distinguish between how much of the fat is visceral and how much is subcutaneous.

Despres and his colleagues discovered a decade ago that people with excess visceral fat have elevated blood levels of triglyceride. The term "hypertriglyceridemic-waist phenotype" was born. The researchers thought it could be a useful and inexpensive way to screen people at risk of coronary artery disease and Type 2 diabetes.

They looked at a group of 21,787 men and women, age 45 to 79, living in Norfolk, U.K., who are participating in a large study investigating cancer and nutrition.

After an average of nearly 10 years of followup, 2,109 developed coronary artery disease.

The rather unwieldy "hypertriglyceridemic-waist phenotype" is defined as a waist circumference of 90 centimetres or more, and a triglyceride level of 2.0 millimoles per litre of blood or more in men, and a waist circumference of 85 centimetres or more, and a triglyceride level of 1.5 mmol/L or more in women.

In both men and women, a large waist circumference or elevated triglycerides increased the risk of developing heart disease. But the combination of the two was associated with the highest risk for both sexes.

Among men, those with a hypertriglyceridemic waist had a 2.4-fold increased risk of developing coronary artery disease over the followup period, compared with men without the "phenotype." For women with the unhealthy high-waist-high-blood-fat combination, their risks for heart disease increased nearly fourfold.

When the researchers controlled for smoking, high cholesterol, high blood pressure and other more traditional risk factors, the risks for men increased by 28 per cent, and by 67 per cent for women.

Despres said it doesn't take expensive testing to identify those at risk -- just a tape measure and a standard lipid test. A lipid test measures total cholesterol. It also measures the amount of fat in the blood -- triglycerides -- but Despres says doctors aren't trained to pay attention to triglyceride levels unless they're quite high.

"We suggest that moderately elevated triglyceride levels, when combined with an elevated waistline, predicts excess visceral fat and heart disease," he said.

Visceral fat cells flood the bloodstream with free fatty acids, which travel to the liver. "Impaired liver function due to liver fat accumulation is becoming a big, big issue in North America. And the liver is key here," Despres said.

A liver loaded with fat is a "dysfunctional liver," he said, "releasing a lot of glucose in the blood -- increasing your risk of diabetes -- and a lot of triglycerides, leading to a lipid profile that will increase the risk of heart disease."

Excess visceral fat also increases substances that contribute to inflammation in the body, increasing the risk of heart disease, he said.