Contrary to previous speculation, a negative side effect of weight loss – increased bone turnover – may not be able to be prevented by weight-bearing exercise.
Weight loss causes the bones in the body to break down and for new bone to form at a faster than usual rate. This ‘remodelling’ causes a reduction in bone density and therefore increased fragility. Researchers have previously found that weight-bearing exercise encourages bone strengthening, a finding which led to the theory that this type of exercise could prevent bone turnover during weight loss. However, researchers from the University of Missouri discovered that weight-bearing exercise did not prevent this increase in bone turnover.
Study author and associate professor from the University of Missouri, Pam Hinton, said, ‘Accelerated bone turnover is not favourable, but the potential negative consequences of increased bone turnover do not outweigh the numerous other health benefits of weight loss. Adequate intake of calcium and vitamin D may minimise the reduction in bone density during weight loss.’
Hinton and her research team from the Department of Nutrition and Exercise Physiology in the MU College of Human Environmental Sciences studied bone turnover markers in the blood of premenopausal, overweight women. These markers are released by the cells involved in the remodelling, so give a good indication of activity.
Over a six-week period, women who were placed on a diet which resulted in a five per cent loss in body weight and who also took part in weight-bearing exercise (fast walking or running) displayed an increase in bone turnover markers. The same increase in bone turnover was also observed in two other groups of women who had lost five per cent of their body weight, the first through diet only and the second through a combination of diet and non-weight-bearing exercise. The fact that the bone turnover rate remained the same in all of the groups suggests that weight-bearing exercise does not prevent the increase in bone turnover caused by weight loss.
Hinton said, ‘These findings should not affect the prescription for aerobic exercise during weight loss. The rationale for recommending aerobic exercise during weight reduction is to increase energy expenditure and maintain lean body mass.’