How much leucine
is optimal in a single setting?
Evidence seems to suggest that leucine has to be consumed with a mixture of essential amino acids. For example young individuals administered 1.7 grams of leucine in a 7 gram Essential Amino Acid mixture experience increased protein synthesis (Katsanos et al. 2006). When lowering other EAAs and increasing leucine content to 2.8 grams no further increases in protein synthesis are seen. However, when increasing EAAs up to 15 grams, with a leucine content of 2.8 grams, protein synthesis is doubled relative to the 7 gram EAA mixture with 1.7 grams of leucine in it. Therefore approximately three grams of leucine from a 7 to 15 gram mixture of EAAs is beneficial for protein balance.
However, this did not definitively show what the ceiling actually was. Through there is recent evidence that 10 grams of EAAs is able to maximally stimulate protein synthesis
(Cuthbertson et al., 2005). What is also known is that 40 grams of EAAs do not appear to stimulate protein synthesis more than 20 grams of EAAs, suggesting that the limit lies between 10 and 20 grams, at approximately 3 grams of leucine per bolus.
Finally we can also infer optimal leucine intake based on whole protein intake. Dangdin and colleages (2002) had participants consume 22 grams of whey protein compared to 33 grams of whey protein and found that protein synthesis increased. The whey contained approximately 10.1 % leucine content, meaning the participants consumed 2.2 grams to 3.3 grams of leucine and experienced increases in protein synthesis. However, in reality the investigators actually had administered 0.31 g of leucine in the low condition and 0.48 grams of whey per kg of bodyweight, in the high protein condition ( the average protein consumed was 33 based on participants weight in the study). In a 200 pound bodybuilder this would amount to 43 grams of protein or roughly 4.3 grams of leucine. Based on this we have an upper limit of 0.048 grams of leucine per kg of bodyweight per serving for a bodybuilder.
From current evidence we can make the following range of conclusions
1. Most likely an individual will be able to maximally stimulate protein synthesis at approximately 3 grams of leucine in a single serving. Evidence suggests that individuals moving from 1.7 to 2.8 grams of leucine increased protein synthesis when other amino acids were adjusted accordingly.
2. The leucine should be consumed in a supporting EAA mixture. The lower limit of which appears to be 10 grams of EAAs (Cuthbertson et al., 2006). However, taking into account variability and a study conducted by Volpi and colleagues (2001) the range of optimal EAA dosage, given consumption of 3 grams of leucine may increase to 10-15 grams. Because Volpi et al. (2001) did not examine further increases in EAAs we assume that the upper-upper range is somewhere between 15 and 20 grams of EAAs, based on the finding that no further increases in protein synthesis are found between 20 to 40 grams of EAAs.
3. The only study that administered a dosage of protein based on bodyweight that has relevance was conduced by Dangdin and colleagues (2003). They found that a whey protein mixture 0.48 grams of protein per kg of bodyweight stimulated protein synthesis greater than a lower dosage. Based on the above evidence this therefore most likely places an upper limit at around 0.048 grams of leucine per kg of bodyweight per serving, which is roughly 4 grams for a 200 pound bodybuilder. A more conservative number would fall at around 0.04 grams.
Assuming that most high quality proteins such as whey and meats are approximately 10 % leucine then roughly 30 to 40 grams of protein will meet the 3-4 gram leucine standard in a single setting, which is roughly 150 to 200 calories. If consuming an essential amino acid supplement such as the Essential Amino Acid shooter, one serving administers 3 grams of leucine at 45 calories per serving.