Exercise can help people slim down, but those who want to lose substantial amounts of weight and keep it off must make changes in their diets, too, according to a systematic analysis of the best available data.

“Exercise by itself is not going to be an effective weight-loss strategy for an individual. You really need to combine exercise with better nutrition,” Dr. Kelly Shaw of the Department of Health and Human Services in Tasmania, Australia, the study’s lead author, commented in a press release accompanying the study.

But exercise can boost heart health even if it doesn’t result in weight loss, Shaw and her team note.

While studies to date have found exercise alone has little effect on weight loss, the researchers note, being active has been shown to prevent weight gain. To better understand the role of exercise in weight loss, they reviewed 43 exercise clinical trials that lasted at least three months, and included a total of 3,476 overweight or obese people.

Their findings appear in The Cochrane Library, a journal published by an international organization that evaluates health care research.

Low- and high-intensity exercise were equally effective in helping people slim down when combined with dietary changes, Shaw and her team found, but when people relied on exercise alone for weight loss, higher intensity workouts were more effective.

The researchers also found that exercise reduced blood pressure, cholesterol, triglycerides and blood glucose, while increasing levels of “good” HDL cholesterol, whether or not people lost weight. The more intense the exercise, the greater the effect on blood glucose.

They conclude: “Although exercise alone improved weight loss only marginally compared with no treatment in this study, when combined with dietary interventions, the amount of weight loss achieved with exercise increased substantially.”

SOURCE: The Cochrane Library, October 18, 2006.