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. 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.

Developing a new treatment paradigm for disease prevention and healthy aging

“…Current RDAs for protein consumption for middle-aged and older adults (0.8 g/kg bodyweight) and following a usual care low-fat, low-calorie, moderate-protein diet appear inadequate for retention of skeletal muscle mass [39]. Studies suggest that the retention of skeletal muscle mass in middle-aged and older adults may require 1.2 g of protein per kilogram per day (or more) with regular daily meals containing 20-30 g of protein with 8-9 g of essential amino acids with meals distributed and consumed several times per day to optimize the stimulation of MPS [21,40,41].…”

“…However, even with 20 % kilocalorie from protein, this is likely inadequate to maintain lean body mass (e.g., 20 % protein, 1,350 kcal/day, 90 kg bodyweight, 0.75 g protein/kg, below the current RDA). Recent reviews, noted below, suggest that for middle-aged and older adults, RT may be optimized by consuming~1.2 g of protein per kilogram of bodyweight, 108 g of protein per day for a person weighing 90 kg, with 20-30 g of protein in several meals throughout the day [20,21]. Moreover, following usual energy restricted, lower to moderate protein diets and usual physical activity, cycles of weight loss and regain can result in a loss of lean body mass and additional gains in body fat in middle-aged and older adults, even for longer-term programs that effectively reduce weight and only show minimal weight regain [22,23].…”

“…Importantly, such an approach could result in fat mass loss while allowing lean mass accretion through additional protein consumption and RT. DASH's meal composition and plans for distributing protein throughout the day are considered ideal (see later) [21]. DASH is low in saturated fat and emphasizes consumption of fruits, vegetables, low-fat dairy products, whole-grain products, fish, poultry, smaller portions of lean meats and nuts, with minimal sweets, added sugars, and sugarsweetened beverages.…”

Effect of high-intensity exercise and protein supplementation on muscle mass in ADL dependent older people with and without malnutrition — A randomized controlled trial

“…Although the subjectspecific protein doses distributed in connection with the resistance training is not known, studies utilizing protein seem to indicate a plateau in muscle protein synthesis from the ingestion bolus between 20-40 g of protein (12). Similarly, in a study conducted by Symons et al (13), 30 g of protein in the form of beef in a single meal resulted a maximum stimulation of skeletal muscle protein synthesis in both young and old subjects. A threefold increase in protein intake did not further stimulate protein synthesis.…”

Nutritional influences on age-related skeletal muscle loss

“…Recent suggestions are that older adults should consume 1·0-1·2 g/kg/d, although this is debated (259)(260)(261)(262)(263) . It has also been suggested that older people potentially divide protein intake during the day to consume 25-30 g high quality protein per meal in order to maximise protein synthesis (264,265) . At present, there is no recommendation for younger adults although the recommendation to consume 0·8 g/kg/d protein would appear to be wise.…”