Weight-loss enthusiasts often recommend calorie-restriction along with regular exercise to take the extra inches off the waist. However, a new study suggests that this combination may not be good for our bones.
Scientists at the University of North Carolina (UNC) at Chapel Hill conducted research to study the effects of cutting calories (while still taking all the recommended nutrients) along with regular exercise on bone health. They found that the diet-exercise combo may slowly leach our bones, making them weaker and thinner with time.
The research was published in the Journal of Bone and Mineral Research, the official Journal of the American Society for Bone and Mineral Research, on 11 September 2019.
The research, done at the Department of Medicine, Endocrinology Division, was on the effect of 30% calorie restriction in animal models – mice. The mice were split into four different groups: high-calorie diet with exercise and without exercise and low-calorie diet with and without exercise. The mice on a low-calorie diet were given vitamins and mineral supplements so they got their daily nutritional requirements.
After observing them for six days, the scientists noted that the group with the low-calorie diet and exercise had lost some of their bone mass and gained bone marrow fat.
“These findings were somewhat of a surprise for us,” lead researcher Maya Styner said in a UNC press release. “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,” she added
Complexities of the human body
Our bones change constantly as new materials get added and older cells are recycled. The bone marrow — a spongy tissue present in some bones — plays an important role in remodelling our skeletal structure.
Marrow adipocyte tissue (MAT), a small portion of the bone marrow, helps to maintain the homeostasis (stable state) of our bones. It is also essential for the regulation of energy metabolism.
Earlier studies have found an inverse association between calorie reduction and MAT levels – that is, MAT reserves increase when we consume fewer calories for some time. Studies have also found that MAT starts to deplete with regular exercise, but it increases steadily with overeating.
Additionally, scientists believe that MAT functions differently during calorie-deficit – even as the amount of MAT increase, it does not provide the energy our body needs. Thus rigorous exercise with a low-calorie diet may lead to a gradual decline in health.
Further, the increase in MAT with low-calorie diet mirrors bone diseases such as osteoporosis, in which bones become weak and fragile.
This particular study was done on animals. However, there is evidence from previous human studies that suggests that the same mechanisms work in humans, too.
“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,” Styner said. “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.”