A higher daily protein intake did not improve lean body mass or physical strength in older men, according to a randomized clinical trial.
Compared with men who consumed the Institute of Medicine’s recommended dietary allowance of protein (0.8 g/kg/d), those who ate more (1.3 g/kg/d) did not have any significant change in lean body mass after 6 months (effect size 0.31 kg; 95% CI −0.46 to 1.08 kg; P=0.43), reported Shalender Bhasin, MB, BS, of Brigham and Women’s Hospital in Boston, and colleagues.
Similarly, there were no significant improvements in secondary outcomes, including measures of muscle performance, physical function, and self-reported well-being, the team wrote online in JAMA Internal Medicine.
The only significant difference found was a decrease in fat mass among men who consumed the higher amount of protein (difference −1.12 kg; 95% CI −2.04 to −0.21 kg; P=0.02). The mechanisms by which increased protein intake reduces fat mass are not completely understood, but they may include increased energy expenditure due to the thermic effect of protein and changes in gut hormone such as glucagon-like peptide 1, the researchers speculated.
“Many experts have questioned whether the protein recommended dietary allowance is adequate to preserve lean body mass and physical function in older adults.” Previous epidemiological and observation studies have yielded inconsistent results, but nevertheless many national organizations and experts suggest protein intakes greater than the institute’s recommendation in order to maintain and promote protein anabolism in older adults.
“Our findings do not support the recommendation that protein intakes higher than the recommended dietary allowance promote lean body mass accretion or augment anabolic response to a muscle anabolic drug, such as testosterone,” Bhasin and colleagues said. “Protein intake equal to the recommended dietary allowance was sufficient to maintain lean body mass, muscle strength, and physical function in functionally limited older men.”
The Optimizing Protein Intake in Older Men (OPTIMen) study was a randomized, placebo-controlled, double-blind, parallel-group trial with a 2 × 2 factorial design. Included were 92 older men with moderate physical function limitations whose average daily protein intake was less than or equal to the institute’s recommendation. The mean age of the participants was 73, and their mean body-mass index was 30.
The study excluded men with prostate cancer; severe lower urinary tract symptoms; untreated sleep apnea; erythrocytosis; a glycated hemoglobin level greater than 8%; and those who had experienced heart failure, myocardial infarction, or stroke within the past 6 months. All participants were put on an individualized diet based on their energy requirements. They were also randomized to one of the following four protein intake groups:
- 0.8 g/kg/d of protein plus placebo injections weekly
- 1.3 g/kg/d of protein plus placebo
- 0.8 g/kg/d of protein plus testosterone enanthate (100 mg weekly)
- 1.3 g/kg/d of protein plus testosterone
The energy and protein content of each participant’s diet was standardized with packaged meals and supplements. The primary outcome was change in lean body mass at 6 months, measured by dual energy x-ray absorptiometry calibrated using a soft-tissue phantom. Secondary outcomes included measures of strength and physical function, such as chest press strength and 6-minute walking distance, as well as health-related quality-of-life measures such as the Psychological General Well-Being Index.
The testosterone group was included to investigate whether a higher protein intake enhanced the effects of testosterone. However, the study found that men randomized to testosterone gained significantly more lean body mass than those randomized to placebo (3.54 kg; 95% CI 2.88-4.20 kg; P<0.001) regardless of their protein intake, the researchers said.
Because the study included only older men with moderate physical dysfunction, the results might not apply to other populations, including women, frail older people, or those with multiple comorbidities that could affect lean body mass, Bhasin and colleagues cautioned. In addition, the sample size of 92 was intended to achieve 80% power to detect clinically meaningful effects, “but it provides less assurance of the detection of more subtle differences,” the authors added. “The findings of our study should be interrogated in larger confirmatory studies.”
Bhasin disclosed financial relationships with Novartis, Abbvie, and FPT Corporation; one co-author disclosed financial relationships with several pharmaceutical companies, and another disclosed relationships with the Beef Checkoff Program, the National Dairy Council, and other organizations.