34) J Am Diet Assoc. 2009 Sep 1; 109(9): 1582–1586.

Moderating the portion size of a protein-rich meal improves anabolic efficiency in young and elderly

1. Brock Symons, Ph.D., Post-Doctoral Fellow, Melinda Sheffield-Moore, Ph.D., Associate Professor, Robert R. Wolfe, Ph.D., Professor, and Douglas Paddon-Jones, Ph.D., Associate Professor

Abstract

Ingestion of sufficient dietary protein is a fundamental prerequisite for muscle protein synthesis and maintenance of muscle mass and function. The elderly are often at increased risk for protein-energy malnutrition, sarcopenia and a diminished quality of life. This study sought to compare changes in muscle protein synthesis and anabolic efficiency in response to a single moderate (113 g; 220 kcal; 30 g protein) or large serving (340 g; 660 kcal; 90 g protein) of 90% lean beef. Venous blood and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion (0.08 μmol/kg/min) of L-[ring-¹³C₆] phenylalanine in healthy young (n=17; 34±3yrs) and elderly (n=17; 68±2yrs) individuals. Mixed muscle fractional synthesis rate (FSR) was calculated during a 3 h post-absorptive period and for 5 h following meal ingestion. Data were analysed using a two-way repeated measures ANOVA with Tukey’s pair-wise comparisons. A 113 g serving of lean beef increased muscle protein synthesis by approximately 50% in both young and older volunteers. Despite a 3-fold increase in protein and energy content, there was no further increase in protein synthesis following ingestion of 340 g of lean beef in either age group. Ingestion of more than 30 g of protein in a single meal does not further enhance the stimulation of muscle protein synthesis in young and elderly.