Whey protein stimulates more muscle-building in older men when compared to other proteins because of its superior amino acid profile, according to a new study by researchers from Maastricht University Medical Center in the Netherlands.
The study, published in the American Journal of Clinical Nutrition, reveals that in addition to being a “fast” digesting protein, whey also has a preferable ratio of amino acids for protein retention in the muscles.
As we age, muscle synthesis declines and muscle loss accelerates. Muscle loss is not only a problem in terms of physical activity, total body muscle is also a huge factor in regulating body weight and determining resting metabolic rate. Sarcopenia, or age-related loss of muscle and strength, is becoming an increasingly relevant concern for an aging population and is directly associated with quality of life.
Promoting muscle synthesis through diet and exercise is effective in maintaining long-term health. The authors of the current study suggest that increasing muscle protein synthesis through ingestion of whey proteins may provide “effective nutritional strategies to attenuate age-related losses of muscle mass.”
Higher rates of muscle protein synthesis are likely “attributed to the faster digestion and absorption kinetics of whey, which results in a greater increase in postprandial plasma amino acid availability and thereby further stimulates muscle protein synthesis,” report the researchers.
Although previous research shows that whey protein supports higher levels of protein retention than casein, it has not been clear if retention was due to quick digestion and absorption of whey proteins, or if the amino acid content of whey may have contributed as a factor. Whey, for example, is characteristically higher in branched-chain amino acids, including leucine.
To test the hypothesis that amino acid content played a role, the researchers included hydrolyzed casein protein, which is partially broken-down casein protein, to speed up the digestive process similarly to whey.
The researchers randomly assigned 48 healthy, older men to one of three protein groups. They received a 20-gram drink containing whey, casein or casein hydrolysate protein along with labeled phenylalanine to determine protein fractional synthetic rates. None of the subjects had a history of diabetes or participated in a regular exercise program.
Plasma was collected over a six-hour period and muscle biopsies were taken at baseline and at three and six hours. The appearance of, availability and absorption of amino acids were measured for all three dietary groups.
Results from this carefully monitored study showed both casein hydrolysate and whey increased available amino acids earlier than the non-hydrolyzed casein proteins.
However, the researchers report, “whey protein is more effective than casein and casein hydrolysate at promoting postprandial muscle protein accretion in healthy older men.”
While initial amino acid availability was similar between whey and casein hydrolysate, whey stimulated a higher net availability of amino acids than either casein protein supplement over the six-hour time period. The researchers concluded that rate of absorption is not the only determining factor for after-meal muscle protein retention.
A greater increase in plasma leucine concentrations following whey protein intake “seems to be in line with the suggestion that leucine forms a key factor regulating postprandial muscle protein synthesis.” The amino acid composition within each protein was shown to be as important as rate of absorption in stimulating amino acid uptake.
Reference: Pennings B et al. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. Am J Clin Nutr 2011; 93: 997-1005. doi: 10.3945/ajcn.110.008102.
Editor’s note: Isagenix uses New Zealand-sourced whey and other dairy proteins including casein in IsaLean Shake to take advantage of both fast- and slow-digesting properties to maximize muscle retention through sustained blood amino acid levels, increase thermogenesis, promote satiety, and encourage healthy weight management.
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