Effect of protein supplementation on hip bone mineral density, cortical thickness, and bone strength in older adult participants during a caloric restriction and aerobic exercise weight loss intervention: a randomized controlled trial

UNLABELLED: Weight loss in older age can cause bone loss. In older adults with overweight/obesity in a weight loss trial, 6-month hip bone strength increased with higher protein intake versus controls consuming the Recommended Dietary Allowance. However, greater weight loss was associated with greater 18-month hip bone mineral density loss. PURPOSE: Weight loss (WL) to treat obesity in older age can exacerbate bone loss. METHODS: This trial assessed the effects of higher protein intake on hip bone outcomes in 187 older adults with overweight/obesity participating in 6 months of active WL (caloric restriction + aerobic exercise) followed by a 12-month maintenance phase. Participants were randomized to either the Recommended Dietary Allowance for protein intake of 0.8 g protein/kg body weight/day (RecProt) or higher protein intake of 1.2 g protein/kg/day for the 6-month WL period only (6-mo HiProt) or the full 18-month period (18-mo HiProt). CT scans at baseline, 6 months, and 18 months were analyzed for hip volumetric bone mineral density (vBMD) and cortical thickness; bone strength was assessed via finite element modeling of a sideways fall. Areal (a)BMD was measured with hip dual-energy X-ray absorptiometry. Analyses examined 6-month and 18-month bone changes using analysis of covariance, and Spearman's correlations of WL vs. bone changes. RESULTS: Greater WL was associated with greater gains in hip bone strength (p = 0.007) at 6 months, but greater trabecular vBMD loss at 18 months (p = 0.011) and aBMD loss at 6 and 18 months (p < 0.001). Hip bone strength increased 3.8 ± 1.7% over 6 months in the 18-mo HiProt group vs. 0.5 ± 1.6% in the RecProt group (p = 0.02) despite similar 6-month WL across groups (-8.0 ± 5.0%); however, there were no differences between the other groups. Eighteen-month group differences were non-significant. CONCLUSION: Higher protein intake had a beneficial effect on hip bone strength in older adults with overweight/obesity undergoing a WL intervention over the short-term.