Two-Year Whey Protein Supplementation Did Not Enhance Muscle Mass and Physical Function in Well-Nourished Healthy Older Postmenopausal Women

Background: Protein may play a role in preventing muscle loss with aging. To our knowledge, there have been no long-term randomized controlled trials to examine the effects of increased dietary protein intake on muscle health in community-dwelling older women. Objective: In this study, we evaluated the effects of whey protein supplementation on muscle mass and physical function in community-dwelling older Australian women. Methods: In this 2 y randomized, double-blind, placebo-controlled trial, women aged 70-80 y (mean 74.3 +/- 2.7 y) were randomly assigned to either a high protein drink containing 30 g of whey protein (n = 109) or a placebo drink containing 2.1 g protein (n = 110) daily. Dual-energy X-ray absorptiometry appendicular skeletal muscle mass, upper arm and calf (38% tibia) muscle cross-sectional area, physical function including hand grip strength, lower limb muscle strength and Timed Up and Go test, and 24 h urinary nitrogen were measured at baseline, 1 y, and 2 y. Results: A total of 196 women with at least one follow-up measurement were included in this analysis. Baseline mean BMI was 26.7 +/- 3.9 kg/m(2) and protein intake was 76 +/- 17 g/d (1.1 +/- 0.3 g.kg body weight(-1).d(-1)). A mean increase in protein intake of similar to 20 g/d in the protein group was confirmed by the estimates from 24 h urinary nitrogen. Over the 2 y in both groups there was a significant decrease in the upper arm (mean +/- SE: -5.59 +/- 0.75 cm(2)) and calf (-0.77 +/- 0.11 cm(2)) muscle area, as well as hand grip strength (-1.30 +/- 0.3 kg) (all P<0.05), but appendicular skeletal muscle mass did not change significantly. There were no significant effects of the protein intervention on any of the muscle mass or physical function measures (all P>0.05) at 1 and 2 y. Conclusion: This study showed that in protein-replete, healthy, ambulant, postmenopausal older women, 30 g/d of extra protein did not improve the maintenance of muscle mass or physical function despite evidence of deterioration in muscle measurements in the upper limb.