Protein and healthy aging: optimal muscle mass for life.
Our muscles are constantly in balance between anabolism (growth) and catabolism (breakdown). For anabolism to take place, we need to fuel muscles with protein. Exercise also gives muscles a further push to grow. Optimal distribution of protein at each meal appears to be a key factor in building and maintaining muscle mass throughout life.
Our team has been investigating how North American eating habits pertaining to protein affect the maintenance of muscle mass during the aging process. In one study, we gave subjects a 30-gram serving of protein (115 g lean beef) and, over the next four hours, measured how their muscles responded. There was a robust improvement in protein synthesis in both young and elderly adults, suggesting that aging doesn't inevitably impair our ability to turn dietary protein into muscle.
While a moderate amount of protein (about 30 grams/meal) can increase muscle protein synthesis, there may be a ceiling effect. For most adults, consuming much more protein than 30 grams/meal provides additional energy, but is not likely to provide a further increase in muscle protein synthesis. When young adults halve their protein intake (from 30 to 15 grams/meal), their muscle protein synthesis is also reduced by approximately 50%.
Unfortunately, North American distribution of protein is skewed (i.e., most of it consumed at supper and less at breakfast and lunch) and fails to maximize potential muscle growth and repair. We get the greatest benefit by distributing protein evenly across meals: about 30 grams each at breakfast, lunch and supper (the 30-30-30 g Protein Rule).
Exercise is also important for all ages. We observed as much as an additional 50% increase in protein synthesis when a modest bout of exercise was performed within an hour or two of eating.
References: Symons TB et al. Aging does not impair the anabolic response to a protein-rich meal. Am J ClinNutr2007; 86(2):451-6. Symons TB et al. A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects. J Am Diet Assoc 2009; 109(9):1582-6. Paddon-Jones D, Rasmussen BB. Dietary protein recommendations and the prevention of sarcopenia. Curr Opin Clin Nutr Metab Care. 2009; 12(1):86-90. Review. Symons TB et al. The anabolic response to resistance exercise and a protein-rich meal is not diminished by age. J Nutr Health and Aging (in press).
Douglas Paddon-Jones, Ph.D.
Professor, Nutrition and Metabolism The University of Texas Medical Branch
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|Title Annotation:||nutrition horizons|
|Publication:||Canadian Journal of Dietetic Practice and Research|
|Date:||Jun 22, 2014|
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