Beneficial impact of exercise on bone mass in individuals under calorie restriction: a systematic review and Meta-analysis of randomized clinical trials

Background: A major therapeutic goal in weight management should be total body fat reduction whereas as preserving lean body mass and bone mass density. It is uncertain if an exercise program reduces the adverse effects of calorie restriction-induced weight loss in adults. Objective: The aim of the present study was to evaluate the differences in bone mass between adults who enrolled in a calorie restriction or an exercise-calorie restriction induced weight loss program. Data sources: Both PubMed and Scopus libraries were searched up to February 2020. Methods: Systematic reviews and a meta-analysis were carried out of randomized clinical trials (published to February 2020) on differences in bone mineral density and content (BMD and BMC) of adults who lost weight by calorie restriction alone (CR) or exercise-calorie restriction (CR-E). The study quality was calculated using the Cochrane scoring system. Retrieved data were pooled when weight mean differences (WMDs) were computed between two groups for BMD and BMC at various sites of the body. Results: Thirteen studies, with a total of 852 participants were included. Available evidence found significantly higher BMD at the hip (WMD: 0.03 g/cm(2), 95%CI: 0.01 to 0.04, p <0.001) and femoral neck WMD: 0.03 g/cm(2), 95%CI: 0.01 to 0.05, p <0.001) and total body BMC (WMD: 0.13 kg/cm(2), 95%CI: -0.10 to 0.36, p <0.001) in the CR-E compared to the CR weight loss group. In contrast, all changes in total body BMD (WMD: 0.00 g/cm(2), 95%CI: -0.01 to 0.02, p = 0.57) and lumbar spine BMD (WMD: 0.00 g/cm(2), 95%CI: -0.01 to 0.01, p = 0.89) were not statistically significant. Limitations: Little evidence was available for different sexes separately. Most individuals were postmenopausal females and no subgroup analysis could be conducted based on menopausal status. Conclusion: This study suggests that physical training can preserve and even significantly increase the bone mass of the hip and femoral neck during weight reduction. Of note, various exercise modalities affected BMD at different sites. Similar results were not found for lumbar spine and total body BMD.