Does Protein Intake During Weight Loss Affect Bone Mineral Content and Density?

Abstract

0695 Although the effects of weight loss on bone have not been extensively examined, it is theorized that weight loss has adverse effects on bone health. Moreover, the impact of dietary protein on bone status during weight loss remains unclear. PURPOSE: To evaluate the effects of dietary weight loss regimens varying in macronutrient content on bone mineral content (BMC) and density (BMD) of the whole body (WB), proximal femur (PF) and lumbar spine (LS). METHODS: Fifty-two (21M, 31F), middleaged (M ± SD; 47.9 ± 7.2 y), overweight individuals (BMI = 33.7 ± 4.5 kg/m2) were randomized to a 4-month lifestyle physical activity program and isocaloric (females = 1700 kcal/day and males = 1900 kcal/day) diet consisting of either: A) higher protein (PRO; 1.6 g/kg-day or ∼ 30% protein, 40% carbohydrate and 30% fat) OR B) higher carbohydrate (CARB; 0.8g/kg-day or ∼15% protein, >55% carbohydrate and 30% fat). Body composition and bone measures were acquired using dual energy x-ray absorptiometry (DXA; Hologic 4500A). RESULTS: Weight loss was not statistically different between PRO and CARB (−8.8 ± 4.7 vs.−7.1 ± 4.1 kg, p = 0.16), however, there was a strong trend for greater WB fat loss (−6.0 ± 3.2 vs. −4.5 ± 2.4 kg, p = 0.07) and trunk fat loss (−3.7 ± 2.1 vs. −2.8 ± 1.5 kg, p = 0.05) in PRO. No group or time effect was apparent for WB BMC or BMD. Total PF and PF neck BMD decreased in the total group (−0.6 ± 2.0%, p = 0.03; −0.9 ± 3.0%, p = 0.02) with no group effect. In contrast, PRO significantly increased LS BMC (3.7 ± 4.2 vs. 1.5 ± 3.8%, p = 0.03) and BMD (3.0 ± 3.8 vs. 0.9 ± 2.0%, p = 0.01) compared to CARB. Although no significant change in LS area occurred (p = 0.98), a significant negative relation existed between changes in LS BMC and changes in WB fat, mineral free lean and trunk fat mass (range = −0.37 to −0.48, p < 0.01). Coupled with the divergent effects of weight loss on PF and LS, measurement artifact cannot be discounted. CONCLUSION: Although it appears that weight loss diets higher in protein confer increases in bone health indices, measurement error cannot be dismissed. Additional studies investigating A) the effect of protein intake during weight loss on bone health and B) the accuracy of fan-beam DXA in assessing bone changes during weight loss states are warranted. Supported by National Cattleman's Beef Association