Amalgamation of Exercise and Calorie Restriction Can Be Harmful to Bone Health

Those trying to lose weight who exercise regularly and restrict calories could be putting their bone health at risk, according to a new study. This new research looked at what happens to bone marrow fat and overall bone health when restricting calories.

This new study published in the Journal of Bone and Mineral Research shows how bone density in mammals is decreased when calorie reduction is taking place alongside exercise.

Senior author on the study, Maya Styner, MD, associate professor of medicine at the UNC School of Medicine spoke about the research. “These findings were somewhat of a surprise for us. Past studies in mice have shown us that exercise paired with a normal calorie diet, and even a high calorie diet, is good for bone health. Now we’re learning this isn’t true for exercise along with a calorie-restricted diet.”

The research primarily focused on the fat in bone marrow of mice, which is relatively understood. To date, fat in bone marrow is thought to be harmful to bones of mammals, including humans, because it makes bones weaker. Less fat is usually an indication of better bone health.

Past research from Styner’s team has looked at the effects of calorie consumption on bone marrow fat, along with the impact of exercise. The studies have shown that in obesity caused by excess calories, the amount of bone marrow fat is increased. Exercise in both obese and normal-weight mice decreased bone marrow fat and improved the density of bones.

But this latest study looked at what happens to bone marrow fat and overall bone health when restricting calories. The researchers looked at four different groups of mice who high-calorie into different categories. One group was all fed a regular diet, one had a calorie-restricted diet, one had a regular diet who exercised, and one had a calorie-reduced diet that exercised. Mice in the calorie-reduced diet group ate 30 percent less than the regular diet group.

Styner’s team found that mice in the calorie-restricted group lost weight, but also had an increase in bone marrow fat.

“This was mild caloric restriction, and we found a significant increase of fat in the bone marrow,” Styner said. “This group also had a decrease in bone quantity—they had less bone overall due to the cut in calories.”

Lack of Nutrients

To check that the issue was not due to a lack of nutrients, the calorie-restricted group was given supplements of vitamins and minerals to match the amount the regular diet group received from the extra food they consumed. This was a good indication that the effect on bone density was purely because of the combination of exercise and calorie reduction.

“Looking at this from a human perspective, even a lower calorie diet that is very nutritionally sound can have negative effects on bone health, especially paired with exercise,” said Styner. “This is important for women to consider because as we age our bone health starts to naturally decline. Your calorie intake and exercise routine can have a great impact on the strength of your bones and your risk for break or fracture.”

This study is an excellent reminder to those looking to lose weight, that it isn’t just about losing a few pounds. You must take steps to ensure your weight loss journey is overall healthy for your whole body. Styner’s team of researchers are now planning to conduct more research to understand the purpose of bone marrow fat and why it is affected by diet and exercise.