Debunking the myth that exercising to lose excess body fat, unlike dieting alone, comes at a cost to bone health, researchers at Johns Hopkins have determined that for those age 55 to 75, a moderate program of physical exercise generally maintains bone mass and, in some cases, offers modest improvements.
The Hopkins team showed, in a study to be published in the June issue of the American Journal of Preventive Medicine, that after six months of aerobic exercise on a treadmill, bicycle or stepper, plus weightlifting, subjects experienced better overall fitness and fat loss without much change in bone mineral density. A more detailed analysis revealed slight gains in bone mass, of 1 percent to 2 percent, for those who exercised hardest and showed the greatest increases in aerobic fitness, muscle strength and muscle tissue.
The Hopkins study is believed to be the first to evaluate the effects of exercise independently from other factors, primarily diet, on bone mineral density, a strong gauge of bone health, against the risk of osteoporosis and bone fracture. Indeed, the researchers believe that more intense exercise may demonstrate significantly increased bone mass.
"Older people are very concerned about how best to reduce their body fat as a means of preventing other health problems, such as heart disease and diabetes," says lead study investigator and exercise physiologist Kerry Stewart, Ed.D., a professor of medicine and director of clinical exercise physiology and heart health programs at The Johns Hopkins University School of Medicine and its Heart Institute. "However, excess fat does have the benefit of maintaining bone mass. But fat loss through diet alone can lead to loss of bone, worsening the body's natural bone loss due to aging, a major risk factor for bone fractures."
According to Stewart, most existing studies about the effects of exercise on bone had several limitations to their findings. Many enrolled only women, for example, who are more prone to bone loss after menopause. Others combined dieting and exercise, obscuring the source of the impact. None examined the effects of exercise on bone while also factoring into account the weight and fat changes resulting from it.
For a six-month period, the Hopkins team assessed the benefits of a supervised program of exercise training in a group of 104 older men and women, measuring both fitness and fatness levels at the start and end of the study. All of the participants were in general good health except for untreated, mild hypertension. Half were randomly placed in a widely recommended moderate exercise program, believed to improve fitness, heart health and body composition, while the rest maintained their usual physical routine and diet.
The active group participated in a supervised series of exercises for 60 minutes, three times per week. The combination of exercises was designed to work all major muscle groups, the heart and circulation.
Substantial improvements were observed in active participants' body fat, and muscle and fitness levels.
Aerobic fitness, as measured by peak oxygen uptake on a treadmill, increased by 16 percent, and strength fitness increased by 17 percent. The average weight loss in this group was only four pounds, because much of the loss of fat was offset by increased muscle mass. The fat in the abdominal region, measured by magnetic resonance imaging, was reduced by 20 percent among exercisers. The group that was not exercising had either no or significantly less improvement than the exercising group.