Researchers from St. Louis University's Doisy College of Health Sciences recruited 34 people between the ages of 50 and 60, who were either overweight or toward the high end of normal weight. The participants were split into two groups -- the first group of 18 was put on a diet, while the second group of 16 exercised.
The dieting group reduced their total calorie intake by 16 percent per day for the first three months of the study. For the final nine months, the dieters reduced their caloric intake by 20 percent.
The second group exercised to burn 16 percent of their caloric intake per day for the first three months, then increased their workouts to burn 20 percent of their calories for the final nine months.
By the study's end, both groups lost roughly 9 to 10 percent of their total body weight. However, the researchers found that the participants of the dieting group lost muscle mass during their weight loss, while the exercising group did not.
"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," said Edward Weiss, the study's lead author.
Though the most effective weight loss strategy is to combine diet and exercise, the researchers emphasized that people who only exercise to lose weight are missing out on some unique health benefits of calorie restriction.
"It's important that dieting not be seen as a bad thing because it provides enormous benefits with respect to reducing the risk of disease and is effective for weight loss," Weiss said. "Furthermore, based on studies in rodents, there is a real possibility that calorie restriction provides benefits that cannot be achieved through exercise-induced weight loss."