Researchers from Washington University in St. Louis recruited 48 non-obese, healthy men and women for a one-year study. The participants were randomly assigned to one of three groups. The first group reduced caloric intake by 16 percent for the first three months of the study, then increased calorie restriction to 20 percent for the remaining nine months.
The second group exercised to burn an extra 16 percent of calories during the first three months of the study, then increased daily exercise to burn an additional 20 percent of calories for the last nine months. The exercise group's burned calories were tracked with heart rate monitors.
The remaining participants were used as the control group, and were not assigned a diet or exercise program.
At the end of the study, the dieting group lost an average of 17 pounds, while the exercise group lost an average of 14 pounds. However, the researchers found that the dieting group also lost an average of 2 percent bone mineral density at sites in the spine, hips and leg.
The exercising group experienced no such bone mineral density loss, while the control group lost neither weight nor bone density.
The study's lead author, associate professor of medicine Dr. Dennis T. Villareal, recommended overweight people combine exercise and diet to lose weight. "That way, you get the weight loss benefits of the diet, but prevent the negative effect on bone health," he said.