Sarcopenia, leucine and protein

Ageing is associated with a gradual loss of skeletal muscle mass, known as sarcopaenia . These age-related changes in skeletal muscle mass are attributed to a disruption in the regulation of skeletal muscle protein synthesis and/or degradation
Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy, young individ¬uals. In the elderly, the muscle protein synthetic response to food intake seems to be blunted, which is likely due to impaired anabolic signalling in skeletal muscle tissue and may be a key factor in the aetiology of sarcopaenia.
In addition to food intake, physical activity can effectively modulate muscle protein metabolism, stimulating both muscle protein synthesis and breakdown. However, post-exercise net protein balance will remain negative in the absence of food intake Recently, Koopman and colleagues have reported that co-ingestion of protein and leucine with carbohydrate following physical activity can increase muscle protein synthesis to the same extent in young and elderly lean men
The latter indicates that the combined ingestion of carbohydrate and protein with additional free leucine might indeed represent an effective strategy to further increase muscle protein synthesis and/or to inhibit protein degradation following physical activity. Follow-up studies have shown that leucine has the ability to function as a nutritional signalling molecule that stimulates muscle protein synthesis at the level of translation initiation through the activation of mTOR
In addition, leucine has also been shown to have the potential to affect muscle protein metabolism by decreasing the rate of protein degradation . most likely by stimulating insulin secretion.
In previous studies, Koopman et al have shown that the combined ingestion of carbohydrate, protein and leucine is more effective than the-ingestion of only carbohydrate in stimulating muscle protein synthesis in vivo in man. More recent data suggest that the intake of amino acid mixtures or proteins with additional leucine can further enhance muscle protein synthesis in the elderly. However, the proposed surplus value of leucine co-ingestion under normal living conditions, in which physical activity is followed by food intake, has not yet been assessed.
In a study reported in the British Journal of Nutrition , Koopman et al determined the potential surplus value of free leucine co-ingestion on post-exercise muscle protein synthesis in elderly men (about 75 years old) under conditions where large amounts of whey protein and carbohydrate are being ingested.
However the ingestion of leucine, carbohydrate and protein following physical exercise in the elderly does not increase muscle protein .
Koopman et al 2008 Co-ingestion of leucine with protein does not further augment post-exercise muscle protein synthesis rates in elderly men British Journal of Nutrition vol 99 57-580.

Martin Eastwood

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