By Barbara A. Brehm, Ed.D.

When does being somewhat overweight increase your risk of heart disease? When that extra fat is carried on the torso, most commonly around the middle. Fat in this area (a so-called “apple” shape) is associated with several metabolic conditions that contribute to the buildup of plaque in the blood vessels, including the arteries that nourish the heart. Extra fat carried primarily in the hips and thighs (a “pear” shape) appears to pose less of a health risk.

Why is abdominal fat more harmful to your health?

Extra abdominal fat contributes to premature artery disease in three ways: It increases blood cholesterol levels, decreases the body's ability to use insulin effectively and raises blood pressure.

Abdominal fat, particularly the fat located around the abdominal organs, is metabolically more active than fat in other regions. It increases the amount of fats in the bloodstream going to the liver, a metabolically active organ. This high level of blood fats causes the liver to manufacture substances called lipoproteins to carry fat and cholesterol in the bloodstream. The type of lipoproteins manufactured in response to a high-blood-fat level (low-density lipoproteins, or LDLs) are associated with an increased blood cholesterol level and increased risk of artery disease.

But that's not all. Abdominal fat is also associated with a disruption of blood sugar control that can result in type 2 diabetes mellitus. In this condition, the cells have trouble using insulin, an important hormone that helps blood sugar get into the cells where it can be stored or used for energy. Since the sugar can't get into the cells, it remains in the blood, a condition known as hyperglycemia, or high blood sugar, which is symptomatic of diabetes. Diabetes increases a person's risk of artery disease.

High blood pressure often accompanies extra abdominal fat. The high blood-insulin levels affect the nervous system in a way that increases the resistance of blood flow through the arteries. Insulin also causes the kidneys to excrete less sodium, which increases blood volume and blood pressure.

Why do some people carry extra fat in the abdomen, while others carry it in their hips and thighs?

An individual's pattern of fat distribution is genetically determined. It is also affected by age and gender. Men are more likely to store extra fat in the abdominal area than in the lower body, while women are more likely to carry extra weight in the hips and thighs. After menopause, abdominal fat increases for many women. Extra abdominal fat is a risk factor for both men and women.

Are there special exercises I can do to get rid of extra abdominal fat?

A weight-reduction program based on regular exercise and a low fat, nutritious diet is the only way to decrease body fat. The pattern of fat loss varies from person to person, but fat is generally lost from all over the body. There is no way (short of surgery) to direct the location of fat loss, or to redistribute fat to other parts of the body. Doing 100 sit-ups a day will increase the strength and endurance of your abdominal muscles, but it will not decrease the amount of fat stored around your middle.

I used to exercise regularly, but I never lost any weight, so I quit.

Exercise improves blood cholesterol levels and the body's ability to use insulin effectively, even if you don't lose any weight, so keep exercising. However, most people can lose weight if they exercise regularly and are careful about what they eat. Your fitness instructor might be able to help you design a more effective weight control program that will reduce both your heart disease risk and your weight.