Impact of the macronutrient composition of a nutritional supplement on muscle protein synthesis rates in older men: A randomized, double blind, controlled trial

Abstract

Context:Animpaired muscle protein synthetic response to feeding likely contributes to muscle loss with aging. There are few data available on the effect of the macronutrient composition of clinical supplements on the postprandial muscle protein synthetic response in older subjects. Objective: The objective of the study was to determine the impact of the macronutrient composition of a nutritional supplement on the postprandial muscle protein synthetic response in older men. Methods: A total of 45 nonsarcopenic older men (aged 69±1 y; body mass index 25.7±0.3 kg/m2) were randomly assigned to ingest 21 g of leucine-enriched whey protein with carbohydrate (9 g) and fat (3 g) (Pro-En), an isonitrogenous amount of 21 g of leucine-enriched whey protein without carbohydrate and fat (Pro), or an isocaloric mixture (628 kJ) containing carbohydrate and fat only (En). Stable isotope tracer methodology was applied to assess the basal as well as the postprandial muscle protein synthesis rates in the three groups. Results: Ingestion of protein in the Pro-En and Pro groups significantly increased muscle protein synthesis rates when compared with the basal rates (from 0.032 ± 0.003%/h to 0.05%/h 3 ± 0.004%/h and 0.040%/h ± 0.003%/h to 0.049%/h ± 0.003%/h, respectively; P