Most athletes easily exceed the recommendations for daily protein intake. However, in order to optimise the effects of training, it is still important to understand the amount of protein needed in each meal. Studies have demonstrated that 20-25 grams per meal results in optimal effects. But a group of researchers from the University of Stirling led by Professor Kevin Tipton challenged this thinking! In this blog we will review the literature and discuss these new results.
Three independent studies suggested that 20 to 25 g of protein would be required to reach these optimal effects on protein synthesis (1,2,3). Ingesting higher amounts of protein than this (e.g., 40 g) did not further stimulate muscle protein synthesis after resistance exercise. Similar results have been reported at rest using whole food (lean minced beef) in young men and women where a moderate (~ 30 g protein) amount was just as effective as a high (~ 90 g protein) amount for stimulating muscle protein synthesis (3). Based on these studies, recommendations are currently to take 20-25g of protein per meal with 8-10 grams of essential amino acids and about 3 grams of leucine. If more protein is ingested, the amino acids are simply oxidized and/or excreted as urea.
However, recently it was suggested that larger amounts may be needed for optimal adaptations. Macnaughton et al (3) argued that in previous studies, smaller muscle groups were trained and when larger muscle mass is involved (as would be the case for most athletes and most practical situations), larger amounts of protein may be required. When these researchers at the University of Stirling in Scotland performed a study in which volunteers trained a larger muscle mass, and then consumed different amounts of protein, there were two main observations. The first one was that protein synthetic rates were lower than previous studies, possibly because the same amount of protein now had to be shared with a larger amount of muscle. In the figure above a comparison is made with an earlier study by the same research group (2). Secondly, they observed that ingesting 40 grams of protein resulted in greater protein synthesis than 20 grams of protein, in contrast to previous studies, including their own. The authors discuss that perhaps when larger muscle groups are trained, a higher protein intake is required.
This findings raise a lot of new questions about what the guidelines should be. It seems clear though that more studies are needed to distil new guidelines from these data. Till that time the current guidelines are a great starting point: 20-25g of protein, containing about 8-10g of essential amino acids and 3 grams of leucine at regular (3-4h) intervals.
References
1. Moore et al. Am J Clin Nutr. 89(1):161-168, 2009.
2. Witard et al Am J Clin Nutr 2014;99:86–95
3. Symons et al J Am Diet Assoc. 2009 109(9): 1582–1586
4. MacNaughton et al Physiol Reports 4:15, 2016