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Original Investigation
April 2018

Effect of Protein Intake on Lean Body Mass in Functionally Limited Older Men: A Randomized Clinical Trial

Author Affiliations
  • 1Research Program in Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital, Boston, Massachusetts
  • 2Department of Medicine, Endocrinology, Diabetes, Nutrition and Weight Management, Boston Medical Center, Boston, Massachusetts
  • 3Institute for Aging Research, Hebrew SeniorLife, Boston, Massachusetts
  • 4Department of Medicine/Preventive Medicine and Epidemiology, Beth Israel Deaconess Medical Center, Boston, Massachusetts
  • 5Section of Preventive Medicine and Epidemiology, Boston University School of Medicine, Boston, Massachusetts
  • 6Department of Nutrition Science, Purdue University, West Lafayette, Indiana
JAMA Intern Med. 2018;178(4):530-541. doi:10.1001/jamainternmed.2018.0008
Key Points

Question  Is protein intake greater than the recommended dietary allowance needed to maintain lean body mass in older adults?

Findings  In this randomized clinical trial of 92 men with physical functional limitations, changes in lean body mass, muscle strength and power, and physical function did not differ between men who consumed controlled diets containing the recommended dietary allowance and men who consumed a higher amount of protein (1.3 g/kg/d) for 6 months.

Meaning  The recommended dietary allowance for protein is sufficient to maintain lean body mass; protein intake exceeding the recommended dietary allowance does not increase lean body mass in functionally limited older men who are eating less than the recommended dietary allowance.


Importance  The Institute of Medicine set the recommended dietary allowance (RDA) for protein at 0.8 g/kg/d for the entire adult population. It remains controversial whether protein intake greater than the RDA is needed to maintain protein anabolism in older adults.

Objective  To investigate whether increasing protein intake to 1.3 g/kg/d in older adults with physical function limitations and usual protein intake within the RDA improves lean body mass (LBM), muscle performance, physical function, fatigue, and well-being and augments LBM response to a muscle anabolic drug.

Design, Setting, and Participants  This randomized clinical trial with a 2 × 2 factorial design was conducted in a research center. A modified intent-to-treat analytic strategy was used. Participants were 92 functionally limited men 65 years or older with usual protein intake less thanor equal to 0.83 g/kg/d within the RDA. The first participant was randomized on September 21, 2011, and the last participant completed the study on January 19, 2017.

Interventions  Participants were randomized for 6 months to controlled diets with 0.8 g/kg/d of protein plus placebo, 1.3 g/kg/d of protein plus placebo, 0.8 g/kg/d of protein plus testosterone enanthate (100 mg weekly), or 1.3 g/kg/d of protein plus testosterone. Prespecified energy and protein contents were provided through custom-prepared meals and supplements.

Main Outcomes and Measures  The primary outcome was change in LBM. Secondary outcomes were muscle strength, power, physical function, health-related quality of life, fatigue, affect balance, and well-being.

Results  Among 92 men (mean [SD] age, 73.0 [5.8] years), the 4 study groups did not differ in baseline characteristics. Changes from baseline in LBM (0.31 kg; 95% CI, −0.46 to 1.08 kg; P = .43) and appendicular (0.04 kg; 95% CI, −0.48 to 0.55 kg; P = .89) and trunk (0.24 kg; 95% CI, −0.17 to 0.66 kg; P = .24) lean mass, as well as muscle strength and power, walking speed and stair-climbing power, health-related quality of life, fatigue, and well-being, did not differ between men assigned to 0.8 vs 1.3 g/kg/d of protein regardless of whether they received testosterone or placebo. Fat mass decreased in participants given higher protein but did not change in those given the RDA: between-group differences were significant (difference, −1.12 kg; 95% CI, −2.04 to −0.21; P = .02).

Conclusions and Relevance  Protein intake exceeding the RDA did not increase LBM, muscle performance, physical function, or well-being measures or augment anabolic response to testosterone in older men with physical function limitations whose usual protein intakes were within the RDA. The RDA for protein is sufficient to maintain LBM, and protein intake exceeding the RDA does not promote LBM accretion or augment anabolic response to testosterone.

Trial Registration  clinicaltrials.gov Identifier: NCT01275365