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

Abstract

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.

Figure 1.. CONSORT Diagram Showing the Flow of Participants in the OPTIMen Trial by Receipt of Protein, Placebo, and Testosterone Enanthate (100 mg Weekly)

BMI indicates body mass index (calculated as weight in kilograms divided by height in meters squared); CONSORT, Consolidated Standards of Reporting Trials; OPTIMen, Optimizing Protein Intake in Older Men; and SPPB, Short Physical Performance Battery.

Figure 2.. Changes in Body Composition Measures

A through D, Change in whole-body and regional lean and adipose tissue mass in kilograms from baseline was assessed using dual-energy x-ray absorptiometry. The number of randomized participants in each of the 4 intervention groups who contributed the data at each time point is shown at the bottom of the graphs. The P values, derived from the mixed-effects regression model framework, for the protein-level effect (0.8 vs 1.3 g/kg/d) and testosterone effect (testosterone vs placebo) are also shown. The months represent the time points (0, 3, and 6 months) at which the measurements were performed. Error bars indicate 95% CIs.

Figure 3.. Changes in Measures of Skeletal Muscle Performance

A through C, Maximal voluntary strength measured as 1-repetition maximum in the leg press and chest press exercises and leg press power was assessed using the Keiser chest press and leg press machines (Keiser Sports). The number of randomized participants in each of the 4 intervention groups who contributed the data at each time point is shown at the bottom of the graphs. The P values, derived from the mixed-effects regression model framework, for the protein-level effect (0.8 vs 1.3 g/kg/d) and testosterone effect (testosterone vs placebo) are also shown. The months represent the time points (0, 3, and 6 months) at which the measurements were performed. Error bars indicate 95% CIs.

Figure 4.. Changes in Performance-Based Measures of Physical Function

A through D, Loaded walking speed plus unloaded and loaded stair-climbing (per Muscle Performance subsection on page 5 and Figure 4) power were assessed. The number of randomized participants in each of the 4 intervention groups who contributed the data at each time point is shown at the bottom of the graphs. The P values, derived from the mixed-effects regression model framework, for the protein-level effect (0.8 vs 1.3 g/kg/d) and testosterone effect (testosterone vs placebo) are also shown. The months represent the time points (0, 3, and 6 months) at which the measurements were performed. Error bars indicate 95% CIs.