NEW YORK (Reuters Health) - Caloric reduction and exercise-induced weight loss both substantially improve risk factors for type 2 diabetes; however, one approach does not appear to be better than the other, a study shows.

"Although diet and exercise can markedly reduce the incidence of type 2 diabetes, the relative contributions of exercise training and calorie restriction to these protective effects are not known," note the researchers in the American Journal of Clinical Nutrition.

Data from the present study suggest that weight loss induced by exercise and by dieting are not different with respect to their abilities to improve glucose tolerance and insulin action, "and presumably, to lower the risk of type 2 diabetes," they point out.

To determine the differing effects of exercise and dieting on blood sugar regulation, Dr. Edward P. Weiss and colleagues from Washington University School of Medicine in St. Louis conducted a year-long study, in which they randomly assigned 46 mostly overweight, but not obese, sedentary men and women between 50 and 60 years of age to one of two weight-loss interventions -- exercise training or calorie restriction -- or to a healthy lifestyle "control" group.

According to the team, weight losses achieved by 1 year of exercise with no change in food intake or 1 year of calorie restriction resulted in significant and similar improvements in glucose tolerance and insulin action.

Weight losses achieved with either approach normalized body weight in 52 percent of the overweight men and women in the study.

"On average, participants in our study performed 60 minutes of cardiovascular exercise, such as brisk walking, almost every day of the week and this resulted in weight loss of approximately 16 pounds in 1 year," Weiss told Reuters Health. "Some participants performed substantially more exercise (up to 90 min/d) and had much greater weight loss (30-40 lbs)."

A caveat, Weiss said, "is that food intake must not increase when a person starts an exercise program to lose weight. Many people think that is okay to eat more food if they exercise or that they need to drink sports drinks or eat energy bars if they exercise. However, a modest increase in food intake can quickly offset the calorie-burning benefit of substantial amounts of exercise," he warned.

The findings from this study, Weiss emphasized, should not be taken to indicate that all aspects of health benefit equally from caloric restriction and exercise-induced weight loss. "For example, we recently published a paper showing that exercise provided greater benefits than caloric restriction with respect to muscle strength and cardiovascular fitness and will soon publish additional papers showing that other areas of health may benefit more from one intervention or the other."