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Leucine is one of the three branched chain amino acids (BCAAs) and is frequently referred to as the main amino acid since it is responsible for the most well-known BCAA advantage like muscle growth. Leucine activates the mTOR protein, which subsequently triggers muscle protein synthesis via S6K; the other two BCAAs may also activate mTOR, but their effects are considerably less than leucine’s (and as such, 5g of leucine will be more effective than 5g mixed BCAAs). HMB, a leucine metabolite, is likewise less efficient than leucine at inducing muscle protein synthesis, but being better at preserving lean mass.

Leucine differs from the other two BCAAs, isoleucine and valine, in that it has been tested in isolation rather than in a BCAA combination, whereas the other two BCAAs have not been researched as well.

The majority of leucine research focuses on muscle protein synthesis after a test meal or when more leucine is given to the diet. It appears that leucine can dependably enhance muscle protein synthesis following test meals. However, whether this results in increased lean mass over time is less certain, as leucine appears to be more effective in promoting muscle growth in those who consume less protein in their diet and in the elderly (who tend to have impaired muscle protein synthesis in response to the diet).

The effects of leucine on glucose remain unclear. Leucine has both blood sugar-lowering and blood sugar-raising characteristics (it can release insulin from the pancreas and may directly promote glucose absorption into a cell without insulin) (via stimulating S6K, it can inhibit insulin-stimulated glucose uptake). Leucine increases glucose absorption for up to 45 minutes in a cell culture before hindering itself, whereas acute dosages of leucine appear to have little effect in live systems (some limited evidence that leucine can be rehabilitative in diabetes, but this is preliminary). Isoleucine is a more powerful hypoglycemic agent, although it has less self-inhibition.

How to Take

For acute use, leucine is usually supplemented in the 2,000-5,000mg range.

It’s usually consumed either fasting or with meals that have a naturally low protein level (or protein sources that are low in leucine).

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