Purpose of review To draw attention to recent work on the role of protein and the amount of protein needed with each meal to preserve skeletal muscle mass in ageing. Recent findings Ageing does not inevitably reduce the anabolic response to a high-quality protein meal. Ingestion of approximately 25–30 g of protein per meal maximally stimulates muscle protein synthesis in both young and older individuals. However, muscle protein synthesis is blunted in elderly when protein and carbohydrate are coingested or when the quantity of protein is less than approximately 20 g per meal. Supplementing regular mixed-nutrient meals with leucine may also enhance the muscle protein synthetic response in elders. Summary On the basis of recent work, we propose a novel and specific dietary approach to prevent or slow down muscle loss with ageing. Rather than recommending a large, global increase in the recommended dietary allowance (RDA) for protein for all elderly individuals, clinicians should stress the importance of ingesting a sufficient amount of protein with each meal. To maximize muscle protein synthesis while being cognizant of total energy intake, we propose a dietary plan that includes 25–30 g of high quality protein per meal.

Background. Many older individuals decline functionally during hospitalization, and the deleterious consequences of bed rest may be one cause. This study reports on the effect of 10 days of bed rest on multiple functional parameters in healthy older adults. Methods. Healthy older men and women (n = 11, 67 ± 5 years old) remained on bed rest for 10 days continuously, and consumed a eucaloric diet providing the Recommended Dietary Allowance for protein. Measures of lower extremity strength and power, aerobic capacity and physical performance, as well as physical activity were performed before and after bed rest. Results. All measures of lower extremity strength were significantly lower after bed rest including isotonic knee extensor strength (−13.2 ± 4.1%, p =.004) and stair-climbing power (−14 ± 4.1%, p =.01). Maximal aerobic capacity was 12% lower after bed rest (p =.04), whereas measures of physical performance (Short Physical Performance Battery, and a five-item physical performance test) were not significantly different. Voluntary physical activity decreased after bed rest, and the percentage of time spent inactive increased (7.6 ± 1.8%, p =.004). There were no medical complications. Conclusions. In healthy older adults, 10 days of bed rest results in a substantial loss of lower extremity strength, power, and aerobic capacity, and a reduction in physical activity, but has no effect on physical performance. Identification of interventions to maintain muscle function during hospitalization or periods of bed rest in older adults should be a high priority.

Obesity, with its comorbidities such as metabolic syndrome and cardiovascular diseases, is a major public health concern. To address this problem, it is imperative to identify treatment interventions that target a variety of short- and long-term mechanisms. Although any dietary or lifestyle change must be personalized, controlled energy intake in association with a moderately elevated protein intake may represent an effective and practical weight-loss strategy. Potential beneficial outcomes associated with protein ingestion include the following: 1) increased satiety—protein generally increases satiety to a greater extent than carbohydrate or fat and may facilitate a reduction in energy consumption under ad libitum dietary conditions; 2) increased thermogenesis—higher-protein diets are associated with increased thermogenesis, which also influences satiety and augments energy expenditure (in the longer term, increased thermogenesis contributes to the relatively low-energy efficiency of protein); and 3) maintenance or accretion of fat-free mass—in some individuals, a moderately higher protein diet may provide a stimulatory effect on muscle protein anabolism, favoring the retention of lean muscle mass while improving metabolic profile. Nevertheless, any potential benefits associated with a moderately elevated protein intake must be evaluated in the light of customary dietary practices and individual variability.

We recently demonstrated that muscle protein synthesis was stimulated to a similar extent in young and elderly subjects during a 3-h amino acid infusion. We sought to determine if a more practical bolus oral ingestion would also produce a similar response in young (34 ± 4 yr) and elderly (67 ± 2 yr) individuals. Arteriovenous blood samples and muscle biopsies were obtained during a primed (2.0 μmol/kg) constant infusion (0.05 μmol·kg^-1·min^-1) of l-[ ring-²H₅]phenylalanine. Muscle protein kinetics and mixed muscle fractional synthetic rate (FSR) were calculated before and after the bolus ingestion of 15 g of essential amino acids (EAA) in young ( n = 6) and elderly ( n = 7) subjects. After EAA ingestion, the rate of increase in femoral artery phenylalanine concentration was slower in elderly subjects but remained elevated for a longer period. EAA ingestion increased FSR in both age groups by ∼0.04%/h ( P < 0.05). However, muscle intracellular (IC) phenylalanine concentration remained significantly higher in elderly subjects at the completion of the study (young: 115.6 ± 5.4 nmol/ml; elderly: 150.2 ± 19.4 nmol/ml). Correction for the free phenylalanine retained in the muscle IC pool resulted in similar net phenylalanine uptake values in the young and elderly. EAA ingestion increased plasma insulin levels in young (6.1 ± 1.2 to 21.3 ± 3.1 μIU/ml) but not in elderly subjects (3.0 ± 0.6 to 4.3 ± 0.4 μIU/ml). Despite differences in the time course of plasma phenylalanine kinetics and a greater residual IC phenylalanine concentration, amino acid supplementation acutely stimulated muscle protein synthesis in both young and elderly individuals.

Purpose of review To highlight the losses in muscle mass, strength, power, and functional capacity incurred in older adults during bed rest-mediated inactivity and to provide practical recommendations for both the prevention and rehabilitation of these losses. Recent findings In addition to sarcopenic muscle loss, older adults lose lean tissue more rapidly than the young during prolonged periods of physical inactivity. Amino acid or protein supplementation has the potential to maintain muscle protein synthesis and may reduce inactivity-induced muscle loss, but should ideally be part of an integrated countermeasure regimen consisting of nutrition, exercise, and, when appropriate, pharmacologic interventions. Summary In accordance with recent mechanistic advances, we recommend an applied, broad-based two-phase approach to limit inactivity-mediated losses of muscle mass and function in older adults: (i) Lifestyle: consume a moderate amount (25–30 g) of high-quality protein with each meal and incorporate habitual exercise in close temporal proximity to protein-containing meals; (ii) Crises: react aggressively to combat the accelerated loss of muscle mass and function during acute catabolic crises and periods of reduced physical activity. As a base strategy, this should include nutritional support such as targeted protein or amino acid supplementation and integrated physical therapy.

The RDA for protein describes the quantity that should be consumed daily to meet population needs and to prevent deficiency. Protein consumption in ma