Dietary advice for reducing cardiovascular risk

Diet is an important part of coronary heart disease prevention, and a new review of studies finds that dietary advice leads to modest improvement in risk factors such as high cholesterol and blood pressure, especially in people at higher risk.

The Cochrane reviewers looked at 38 studies in which randomly assigned healthy adults received dietary advice in some cases and no advice in others. The recommendations usually focused on reducing fat and salt intake while increasing the intake of fruit, vegetables and fiber.

People who were received advice on their diets increased their fruit and vegetable consumption by 1.25 servings over the course of follow-up. Fiber intake also increased while total dietary fats and saturated fatty acids fell. Researchers also noted what they called “modest” changes for the better in total cholesterol, LDL (or “bad” cholesterol) and blood pressure. In studies that separated effects by sex, women tended to have larger reductions in fat intake.

“Diet is a key health behavior and a definitive review of the effects of dietary advice among healthy people was lacking, “ said lead author Eric Brunner, Ph.D., a reader in the Department of Epidemiology and Public Health at the University College London Medical School. “The key question is whether the general population responds.”

The answer is “yes,” Brunner said, “but the dietary and risk factor changes are modest. Our findings point to the fact that individuals with risk factor elevation — such as high blood pressure or cholesterol — respond better than those at ‘average' levels of risk, even though average coronary heart disease risk in Western populations is very high compared to a country like Japan, where rates of CHD are relatively low.”

Counseling that occurred in health care settings, such as doctors' offices, resulted in greater reductions in fat and increases in fruit and vegetable consumption. However, it was not clear that these changes translate into lowering of blood cholesterol.

High-intensity interventions involving more than three personal contacts were associated with larger effects than those with fewer contacts. However, “there was a dearth of long-duration studies, meaning that we have little idea of the long-term effects of counseling,” Brunner said.

The Cochrane Library is a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

“Our review suggests that the average changes in individual nutrients and related risk factors are likely to be relatively small,” said Brunner. “When taken across the entire diet, however, several small changes in food habits may lead to greater health gains than the estimates would suggest.”

The more effective, higher-intensity interventions uncovered by the dietary counseling review may not mesh with the current U.S. health care system, cautioned Nieca Goldberg, M.D., spokesperson for the American Heart Association and director of the Women's Heart Program at the New York University School of Medicine.

“With the exception of people with diabetes, health insurance does not pay for targeted nutrition counseling,” Goldberg said. “This often turns into a barrier to proper education when the person cannot afford the costs.”

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.cochrane.org for more information.

Brunner EJ, et al. Dietary advice for reducing cardiovascular risk (Review). Cochrane Database of Systematic Reviews 2007, Issue 4.