title: A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects.
abstract: Ingestion of sufficient dietary protein is a fundamental prerequisite for muscle protein synthesis and maintenance of muscle mass and function. Elderly people 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 serving (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 mumol/kg/min) of L-[ring-(13)C(6)] phenylalanine in healthy young (n=17; 34+/-3 years) and elderly (n=17; 68+/-2 years) individuals. Mixed muscle fractional synthesis rate was calculated during a 3-hour postabsorptive period and for 5 hours after meal ingestion. Data were analyzed using a two-way repeated measures analysis of variance with Tukey's pairwise comparisons. A 113-g serving of lean beef increased muscle protein synthesis by approximately 50% in both young and older volunteers. Despite a threefold increase in protein and energy content, there was no further increase in protein synthesis after ingestion of 340 g lean beef in either age group. Ingestion of more than 30 g protein in a single meal does not further enhance the stimulation of muscle protein synthesis in young and elderly.
authors.affiliation: Graduate Center for Gerontology, University of Kentucky, Lexington, USA.
authors.forename: T Brock
authors.initials: TB
authors.lastname: Symons
authors.forename: Melinda
authors.initials: M
authors.lastname: Sheffield-Moore
authors.forename: Robert R
authors.initials: RR
authors.lastname: Wolfe
authors.forename: Douglas
authors.initials: D
authors.lastname: Paddon-Jones
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D001706:Biopsy; D002247:Carbon Isotopes; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000592:standards; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D008460:Meat; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D009747:Nutritional Physiological Phenomena; D009751:Nutritional Requirements; D010649:Phenylalanine / Q000493:pharmacokinetics
chemical_list: D002247:Carbon Isotopes; D004044:Dietary Proteins; D009124:Muscle Proteins; D010649:Phenylalanine
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