Effects of Leucine on Muscle Protein Synthesis in Older Women

Understanding Sarcopenia

A recent study investigated how varying amounts of leucine, an essential amino acid, affect muscle protein synthesis in healthy older women. As people age, they often experience a decline in muscle mass, strength, and overall function, a condition known as sarcopenia. This condition can lead to frailty, impacting balance, gait, and the ability to perform essential daily activities. Older adults with sarcopenia struggle to synthesize sufficient dietary protein, which is crucial for maintaining muscle mass. Research indicates that dietary protein requirements increase with age, necessitating higher protein intake for older adults to effectively stimulate muscle protein synthesis compared to younger individuals.

Study Overview

A team of Canadian researchers conducted a single-blind, randomized parallel group study involving 22 healthy older women aged 65 to 75 years. Participants were assigned to consume one of two meal-like protein beverages, each containing the same protein content but differing in leucine levels. The study aimed to compare the acute hourly and integrated daily rates of muscle protein synthesis in both rested and resistance-exercised leg muscles. The researchers hypothesized that women consuming the beverage with 4.2 grams of leucine would demonstrate higher rates of muscle protein synthesis compared to those receiving 1.3 grams in the control group. The findings were recently published in the American Journal of Clinical Nutrition.

Findings on Muscle Protein Synthesis

Each group consisted of eleven women, who were instructed to drink one of the two beverages twice daily for six days. During this period, all participants underwent unilateral resistance exercises on one leg on two separate occasions. Results indicated that acute hourly muscle protein synthesis increased in both the rested and exercised legs across both groups; however, the increase was more pronounced in the group consuming the beverage with higher leucine content. Additionally, integrated daily rates of synthesis showed improvements in both legs for the treatment group, while the control group only experienced gains in the exercised leg.

Implications of the Study

The study suggests that integrating approximately 4 grams of leucine into the daily diet, as opposed to relying solely on supplements, may enhance muscle protein synthesis in healthy older women compared to beverages with lower leucine content. While further research with larger sample sizes and longer durations is necessary to confirm these findings, the results indicate that leucine may play a significant role in counteracting the muscle mass loss associated with aging.

Reference

Devries, Michaela C., Christopher McGlory, Douglas R. Bolster, Alison Kamil, Maike Rahn, Laura Harkness, Steven K. Baker, and Stuart M. Phillips. “Protein leucine content is a determinant of shorter and longer-term muscle protein synthetic responses at rest and following resistance exercise in healthy older women: a randomized, controlled trial.” The American Journal of Clinical Nutrition 107, no. 2 (2018): 217-226.