ST. LOUIS -- Which works best in fighting the risk factors for diabetes--exercise or diet? It's a toss up, according to a study by Edward Weiss, a Saint Louis University researcher and a member of a Washington University team of scientists examining whether a calorie-restrictive diet can extend people's lifespan. However, there's no toss up when it comes to which offers more benefits when it comes to losing weight, another study by the same group found.

"Both diet and exercise provide profound benefits to reduce the risk of diabetes. Both those who restrict calories and those who exercise benefit from weight loss," Weiss says. "We thought exercise probably would produce greater benefits. But both of these are providing beneficial health improvements."

The researchers studied 50- to 60-year-olds whose body mass index was between 23 and 30, placing them at the high end of normal weight or overweight, but not obese.

The study participants were divided into three groups with 18 each in the diet and exercise groups and 10 in the control group. The year-long study was funded by the National Institutes of Health.

All participants had their insulin action and glucose tolerance, which both are markers for diabetes, evaluated at the beginning and end of the study. In addition, their weight, body composition and energy intake were measured at the beginning of the study and at one-, three-, six-, nine- and 12-month intervals.

Those who restricted calories met weekly with a dietitian who helped them develop individualized menu plans and guided them to reduce portion sizes and replace high calorie foods with lower caloric choices. Their goal was to reduce their calorie consumption by 16 percent the first three months and by 20 percent for the next nine. Their progress was tracked by keeping food diaries and the water test, to measure their amount of energy expended.

Exercisers, or those who expended more calories, had the goal of burning 16 percent more calories for the first three months, increasing to 20 percent the next nine months. They met weekly with a personal trainer and had open access to a fitness center. To meet their goal, they exercised for 60-90 minutes a day and tracked their progress on a heart rate monitor that recorded calories burned.

"As they got fit, the treadmill could be speeded up. They could exercise on a steeper grade, and they could burn more calories," Weiss says. "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."

While those in the control group could request general advice on eating a healthy diet and free passes to a yoga class, few did, Weiss says.

Glucose tolerance and insulin levels improved at about the same levels in both the dieters and exercisers. They also lost weight. Those in the control group didn’t lose weight or have changes to their glucose tolerance or insulin levels.

Both groups lost between 9 and 10 percent of their total body weight. Those who exercised engaged in 60 minutes of cardiovascular activity six times a week, such as a brisk three- to four-mile walk. Those exercisers who worked out for 90 minutes a day took off more pounds–15 to 20 percent of their body weight.

Those who dieted lost muscle mass while those who exercised did not. This is because exercisers routinely challenged their muscles, which prevented muscle tissue from degrading. Dieters didn’t work their muscles as vigorously as those who exercised, according to the study.

"If push comes to shove and somebody wants to know if they should diet or exercise to lose weight, I would suggest exercise, provided they are willing to put in the extra time and effort and not offset the gains they make by eating more,"says Weiss.

The study was published in the November issue of the American Journal of Clinical Nutrition.