Leucine, isoleucine, and valine are the three branched chain amino acids (BCAAs). Amino acids are the building blocks of proteins, and proteins, as you probably know, make up the structure of the body. Amino acids are either produced in the body, they must be supplied from the diet.
Take between 4-20 g per day. The exact dosage and ratio of leucine, isoleucine, valine is still a matter of debate in the literature, but most studies supplemented within a range of 4-20g BCAAs per day.
To date, there is little to no evidence to suggest that taking a BCAA supplement every day comes with any downsides at all. BCAAs are naturally used by the body in some vital roles, so your system is already used to them, and they seem to put no real strain on the body’s systems when consumed, either. Though research is ongoing, a number of studies have looked at whether there are any dangers inherent in the use of BCAAs as a fitness supplement, and the consensus seems to be that they are perfectly safe, with a few (very specific) exceptions.
Those with certain medical conditions – namely those that impair the body’s ability to process amino acids – should not take BCAA supplements. If you have ALS (Amyotrophic Lateral Sclerosis), for instance, you should avoid amino acid supplements unless otherwise directed by your doctor. Those with a rare condition known as maple syrup urine disease should also avoid these products, as should those with ongoing kidney problems, and some researchers have suggested – out of an overabundance of caution, mainly – that women who are pregnant should skip these supplements, too. However, for a healthy individual, BCAAs are quite safe, even if you use them every day.