Although some differences in the rate of muscle loss in adults can be explained by fixed factors, such as gender, much of the remaining variation is unexplained and has led to increasing interest in the influence of lifestyle, particularly in the effects of modifiable factors such as physical activity and diet. According to Clinical Interventions in Aging (May 2015), it appears we do have opportunities to intervene both to prevent and manage sarcopenia with enhanced benefits of exercise training when combined with dietary supplementation and nutritional strategies. More specifics come from the Protein 2.0 Summit, the discoveries of which were published in the American Journal of Clinical Nutrition (June 2015). Here is a summary of the main conclusions:
• In recent years, multiple opinion articles have argued that protein intake closer to 1.6 grams per kilogram of body weight per day may offer health benefits for aging adults beyond those afforded by the current recommended dietary allowance (0.8 grams per kilogram).
• Approximately one-third of adults over 50 fail to meet the RDA for protein, whereas an estimated 10 percent of older women fail to meet even the estimated average requirement.
• Meeting a protein threshold of about 25–30 grams per meal represents a promising strategy to help maintain muscle mass and function in older adults. The distribution of protein across three or more daily meals is seldom discussed, even though National Health and Nutrition Examination Survey (NHANES) data demonstrate that adults in the United States skew their protein and calorie consumption towards their evening meal.
• A seven-day feeding study was conducted to measure changes in 24-hour muscle protein synthesis in response to diets with equal amounts of protein over meals or skewed protein distribution. Over 24-hour periods, muscle protein synthesis was 25 percent higher when the same quantity of protein was evenly distributed across breakfast, lunch, and dinner, compared with a more common or typical pattern of consumption, which tends to be more focused on dinner.
• Amino acid absorption and subsequent stimulation of protein synthesis were limited after ingestion of 10 grams of whey protein, increased substantially after a meal with 20 grams of protein, and was highest after ingestion of 35 grams of protein.
• Compared with younger adults, older men who are hospitalized and potentially anabolic-resistant require a greater protein intake to maximally stimulate the synthesis of muscle protein. To this end, a recent cross-sectional study in healthy adults aged 60 and up reported that men and women consuming at least 25 grams of protein per meal did better than those consuming less. (Keep this in mind if you or a family member become ill or hospitalized. I always send meal replacements as gifts to my loved ones when they are in such a state of need.)
• The distribution of protein throughout the day may also influence functional outcomes associated with frailty and quality of life, such as exhaustion and slow walking speed. Specifically, researchers noted that even though frail, pre-frail and non-frail elderly individuals consumed a similar absolute and relative amount of protein each day (dietary protein consumption of all study participants exceeded the RDA), the non-frail individuals evenly distributed their protein intake across their daily meals, whereas frail and pre-frail individuals skewed their protein consumption towards the noon meal. There is a potential benefit to be gained by incorporating 25–30 grams of protein into each meal throughout the day to optimize muscle growth after meals.
• Although snacking may influence satiety and (positively or negatively) affect protein and caloric intake at subsequent meals, older adults who exhibit snacking behaviour consume, on average, 6 grams more protein daily than their non-snacking counterparts. Although small amounts of protein consumed during a snack are unlikely to acutely influence protein anabolism, there may be health benefits associated with blood glucose balance, optimized total micronutrient intake and satiety. Recent data also suggest that snacking may improve physical function among adults aged 60 and up. Specifically, snacking frequency and percentage of calories from snacking were positively associated with gait speed among older adults participating in the National Health and Nutrition Examination Survey between 1999 and 2002.
• The essential amino acid profile, digestibility, and amino acid bioavailability of protein are critical determinants of its anabolic potential and quality. Yang et al. reported a reduced ability of soy protein isolate to stimulate muscle growth, both at rest and after resistance exercise, compared with a 20-gram dose of whey protein isolate in older men (aged 71). Differences were largely attributed to lower levels of leucine (which plays a huge role in muscle growth and development) after ingesting soy protein. In a recent study in older men (74 years old), taking 2.5 grams of leucine with 20 grams of casein resulted in 22 percent more muscle protein synthesis than taking casein alone. An improvement in muscle protein was also detected when leucine was added to the moderate-protein meals consumed by older adults (4 grams of leucine per meal, over three meals a day for two weeks). A mixture of pea and rice protein may also be beneficial as it is a complete protein source.
• Recent analysis of NHANES data from Americans aged 50 and up reinforces the synergistic relation between dietary protein intake, physical activity, and skeletal muscle mass. These data suggest that strength exercise preserves muscle in older adults when combined with a dietary protein intake that exceeds the current RDA. Creating an effective framework to maximize this synergistic effect requires not only that protein quantity and type of physical activity be considered, but also how timing of ingestion may stimulate maximum muscle protein growth.
• Although the benefits of resistance and aerobic exercise training are unequivocal, some physical activity is clearly preferable to no activity at all. Even moderate amounts of walking may impart a protective effect on muscle mass and metabolic health. In a group of healthy older adults (aged 72), it was recently demonstrated that a 76 percent reduction in total daily step count for two weeks had a significant negative effect on postprandial muscle protein synthesis, insulin sensitivity and inflammatory markers. In longer-duration trials in healthy and frail older adults, consistent improvements in muscle mass and function most often occurred in response to the combination of protein supplementation and exercise training.
• Optimizing the timing of protein ingestion and exercise is a relatively simple strategy to maximize the potential for muscle protein anabolism. About an hour after exercising, the capacity for maximal muscle protein synthesis is potentially increased. It remains to be seen if increasing amino acid availability at the onset of this rebound/recovery period offers an anabolic advantage. For older adults, consuming a moderate amount of protein at breakfast, lunch, and dinner could provide the necessary amino acid precursors and flexibility to allow at least some protein-exercise anabolic synergy, irrespective of when the exercise session or activity of daily living is performed.
