Health authorities have been telling us for years that being overweight is associated with greater risk for cardiovascular disease. But the underlying mechanisms by which excess weight affects the cardiovascular system are still being investigated.

One of the ways excess weight may harm the heart is by increasing the secretion of inflammatory substances called cytokines, which tax the body's immune system and increase the risk of disease. A recent study found that cytokine secretion was reduced in obese women who lost weight over the course of 2 years. The results are published in the Journal of the American Medical Association.

Studying obese women in Italy

Researchers in Italy recruited 120 premenopausal women between the ages of 20 and 46 who were obese (body mass index 30 or more) and who had no history of conditions that could affect their heart disease risk, such as high cholesterol, high blood pressure, and diabetes.

The women were randomly assigned to either an "intervention group" or "control group." Those in the intervention group received detailed advice on how to lose at least 10% of their body weight through a balanced, calorie-reduced diet and increased physical activity; they had regular meetings with dietitians and exercise trainers. The women in the control group simply received general information about healthful eating and exercise, but did not receive any additional support. Blood tests for pro-inflammatory markers and insulin resistance were done before and at the end of the study.

Intervention produces healthy habits

Not surprisingly, the women in the intervention group had greater reductions in their body mass index measurements after two years compared with women in the control group. They were found to be eating fewer calories and less cholesterol and saturated fat than the control group participants. Women in the intervention group were also eating more complex carbohydrates, fiber, and monounsaturated fat than women in the control group.

The "invisible" effects of weight loss

At the same time the women in the intervention group were losing weight and improving their diets, they may also have been lowering their risk for heart disease in other ways. These women had greater reductions in their secretion of certain proinflammatory cytokines - interleukin 6, interleukin 18, and C-reactive protein (CRP) - compared with women in the control group; they also had a reduction in insulin resistance.

Why cytokine secretion decreased

It's important to note that the women in this study not only lost weight but also ate what is generally considered a "heart-healthy" diet - one rich in complex carbohydrates, fiber, and monounsaturated fat. In addition, they balanced their caloric intake with physical activity. It's not clear whether any one of these lifestyle factors (i.e., losing weight, eating heart-healthy diet, exercising) affected the secretion of cytokines more than another. Rather, it was the lifestyle as a whole that produced the changes in the women in this study.

With obesity nearing epidemic proportions and with heart disease the leading killer of American men and women, these results underscore current advice to eat well, exercise, and maintain a healthy weight.