Exercise and Calorie Cutting Lower Diabetes Risk Equally

ST. LOUIS, Nov. 8 -- Eat less? Exercise more? For diabetes prevention, it's a toss up.

Decreasing caloric intake and increasing activity are equally effective at improving glucose tolerance and insulin sensitivity, reported researchers here.

"Both diet and exercise provide profound benefits to reduce the risk of diabetes," said Edward Weiss, Ph.D., of Saint Louis University, and colleagues. "Both those who restrict calories and those who exercise benefit from weight loss."

"We thought exercise probably would produce greater benefits," Dr. Weiss said. "But both of these are providing beneficial health improvements."

In a year-long study, Dr. Weiss and colleagues evaluated nonobese, healthy adults in their 50s who were part of a longevity study. The participants were at the high end of normal in terms of body mass index.

The investigators wanted to see whether energy expenditures achieved through exercise could both produce weight loss and further improve glucose tolerance and insulin action through mechanisms independent of weight loss.

They enrolled 46 sedentary men and women from the ages of 50 to 60 with BMIs of 23.5-29.9 kg/m². The participants were randomly assigned to either 12 months of exercise training or 12 months of calories restriction (18 in each group).

The remaining 10 participants were assigned to a healthy lifestyle intervention as controls. The intervention consisted of advice for a healthy diet if requested, plus free passes to an offsite yoga facility to use at their option, although few took advantage of the classes or advice, the investigators noted.

All participants underwent oral glucose tolerance tests at baseline and at 12 months to measure insulin sensitivity and areas under the curve for both glucose and insulin. The investigators also measured the glucoregulatory factors adiponectin and tumor necrosis factor ?, and used dual-energy x-ray absorptiometry to measure fat mass.

Members of the caloric restriction group met weekly with a dietitian who helped them with individual meal plans, portion-size reduction, and substitution of low-calorie density foods for high-calorie ones. The goal was a 16% reduction in calorie intake for the first three months, and a 20% restriction for the remainder. The dieters were monitored with food diaries and with the doubly labeled water test, a measure of metabolism.

The exercise group members met weekly with an exercise trainer and had open access to a fitness center. They exercised for 60 to 90 minutes daily and tracked their progress on a heart-rate monitor that also recorded calories burned.

"As they got fit, the treadmill could be speeded up," Dr. Weiss said. "They could exercise on a steeper grade and they could burn more calories. All of them learned very quickly the most efficient way to burn more calories was through cardio. If they pushed themselves, the numbers added up quickly."

The authors found that while the exercisers had more rapid results, there were no significant differences in energy deficits between the exercise and diet groups at one year, as shown by changes in body weight and fat mass.

In both the exercise and caloric restriction groups the insulin sensitivity index increased and the glucose and insulin areas under the curve decreased from baseline to the end of the study. There were no significant differences between exercisers and dieters. Among controls, however, insulin sensitivity, glucose, and insulin measured remained unchanged at one year.

In addition, there were "marginally significant" increases in adiponectin, and decreases in the ratio of TNF-? to adiponectin among the exercisers and calorie cutters, but not among controls.

The authors concluded that "weight loss induced by exercise training or calorie restriction improves glucose tolerance and insulin action in non-obese, healthy, middle-aged men and women. However, exercise-induced weight loss does not appear to be greater than that induced by calorie restriction."

Dr. Weiss said that it's still not known whether the combination of exercise and caloric restriction will be able to provide greater benefits that either intervention alone.

The research was funded by the National Institutes of Health.