Exercising while limiting calories could be bad for bone health

A new study published today in the Journal of Bone and Mineral Research shows how bones in mammals are negatively affected by caloric restriction, and in particular by the combination of exercise and caloric restriction. Maya Styner, MD, associate professor of medicine at the UNC School of Medicine, is the lead author of the study.

"These results were a bit of a surprise for us," said Styner. "Previous studies on mice have shown us that exercise associated with a normal caloric diet, and even a high-calorie diet, is good for bone health." Now, we're learning that it's no longer true for exercise with a low calorie diet. "

Styner's research focuses on the fat in the bone marrow of mice. Although the fat in the bones is poorly understood, it is thought to this day that it is harmful to mammalian bones, including the human, as it weakens the bones. Less fat usually indicates better bone health. Styner's earlier studies have focused on the effects of calorie consumption on bone marrow fat, as well as on the role played by exercise. She found that in obesity caused by excess calories, the amount of fat in the bone marrow is increased. Exercise in normal weight and obese mice decreased fat in the bone marrow and improved bone density.

The latest study looked at what happens to bone marrow fat and general bone health when one restricts calories. There were four groups of mice altogether: one group with a normal diet (RD), one group with a restricted calorie diet (CR), one R & D group that had exercised, and one group of CRs that had exercised. The CR group mice ate 30% less than the RD mice ate.

According to the United States Department of Agriculture (USDA), a "moderately active" woman aged about 30 should consume 2,000 calories a day. A 30% reduction would equate to a diet of 1,400 calories a day, which is about the amount suggested to most women trying to lose weight at a pound a week.

Styner discovered that the CR group mice lost weight but also had an increase in bone marrow fat.

"It was a mild caloric restriction, and we found a significant increase in bone marrow fat," Styner said. "This group also had a decrease in the amount of bone – they had overall less bone because of the reduced calories."

Both groups of CR mice were supplemented with vitamins and minerals corresponding to the amount received by the dietary group from the additional food consumed. This, says Styner, indicates that the effect on bone health was due to a caloric restriction, not a lack of nutrients.

When exercise was introduced into the RC group, bone marrow fat decreased as in previous studies, but overall bone quantity and quality also decreased. Instead of making bones more sturdy, exercise has made bones more fragile when they are associated with caloric restriction.

"If we consider this from a human point of view, even a diet that is low in calories and very nutritionally healthy can have negative effects on bone health, especially associated with 39, exercise, "said Styner. "It's important for women to take this into account because, as we get older, the health of our bones starts to deteriorate naturally.Your calorie intake and exercise program can have a significant impact on the resistance of your bones. your bones and your risk of fracture or fracture. "

Styner says her team is now planning to conduct more research to understand the purpose of bone marrow fat and why it is affected by diet and exercise. This study was funded by grants from the National Institutes of Health (NIH) and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).