Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein
The loss of muscle mass associated with aging, a condition called sarcopenia, calls for both lifestyle adjustments, such as engaging in resistance exercise training, as well as nutritional interventions, such as increasing dietary protein intake with supplements. However, calorically dense protein supplements, including the ever-popular whey protein, can impact appetite and cause elderly patients to eat less, which offsets any muscle-stimulating gains of the protein. Therefore, it is necessary to find the most calorically efficient muscle-building supplement to help preserve muscle tissue and function in the aging population.
Essential amino acids have been proven effective at stimulating muscle protein synthesis in the elderly, but the majority of the supplements on the market that contain essential amino acids are made of whey. This is one of the first studies to compare the anabolic effects of free essential amino acids (without the non-essential amino acids) to those of whey protein (which includes essential and non-essential amino acids) in the elderly.
Acute metabolic study
Number of Subjects
65 - 79
Researchers analyzed the response of muscle protein synthesis to consumption of 15 grams of whey protein versus consumption of an isocaloric amount of essential amino acids (EAAs) to determine the most effective approach to stimulating muscle growth in healthy elderly individuals.
Results showed that net phenylalanine uptake (reflecting net gain of muscle protein) was 3 times higher in the EAA group and that fractional synthetic rate (FSR) of mixed muscle protein, a primary indicator of muscle protein synthesis, was greatest in the EAA group as well. See figures 1 and 2 below.
Essential amino acids and whey protein both stimulate muscle protein synthesis in the elderly, with EAAs showing the greatest anabolic effect. EAAs are also a more energetically efficient nutritional supplement due to their minimal caloric load.
What makes EAAs more energetically efficient?
The 15-gram EAA and whey protein supplements used in this study were both 60 calories, but the whey supplement only contained half the EAAs. This suggests that 30 grams or more of whey protein might be needed to produce the same anabolic response as EAAs, which would increase caloric intake, especially when consumed 2 to 3 times a day. That’s an additional 360 calories that can greatly reduce appetite compared to the lighter caloric load of EAAs.
The loss of muscle mass that accompanies aging can greatly reduce functionality and quality of life. Nutritional therapies to help sustain muscle mass have mixed results, as many can unwittingly act as meal replacements and compromise appetite so that improvements are stalled. Essential amino acids are a promising nutritional intervention for maintaining muscle mass in the elderly, especially since they contain minimal calories and do not adversely affect appetite.
Paddon-Jones D, Sheffield-Moore M, Katsanos CS, Zhang XJ, Wolfe RR. Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein. Exp Gerontol. 2006;41(2):215-219. doi:10.1016/j.exger.2005.10.006