Thank you. This is an important point. The PDCAAS was focused on obtaining sufficient amounts of the essential amino acids that cannot be biosynthesized in people. However, in the last couple decades, growing work on metabolism has shown that different amino acids have different health consequences, so that while you need cross the minimum threshold, that is easy to do, and excess consumption of some amino acids is likely harmful. This is a nice review of dietary effects on metabolism: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8841109/

Here is a relevant quote from the article: "In addition to reducing the availability of total dietary protein, there are several reports of lifespan extension from restriction of specific essential amino acids, which must come from the diet and cannot be synthesized endogenously. The earliest of these may be from Segal, who published in 1977 that restriction of dietary tryptophan delayed growth, reduced cancer, and increased lifespan in rats (51). Orentreich and colleagues later found that restriction of dietary methionine (or more properly sulfur amino acids which include both cysteine and methionine) similarly increased lifespan in rats (52). These seminal discoveries went largely unappreciated for many years but have gained attention as others reproduced and extended these findings to yeast, worms, fruit flies, and mice (53). More recently, restriction of the dietary branched chain amino acids (BCAAs) leucine, valine, and isoleucine has also been found to increase lifespan and delay age-related frailty in both fruit flies (54) and mice (55). BCAA restriction appears to increase lifespan via inhibition of mTOR signaling (discussed further below). Other studies show that restricting methionine and cysteine are key to promoting a protective DR-mediated stress response that is blocked with mTOR activation. Interestingly, this sulfur amino acid restriction appears to be mediated through a mechanism that involves increased production of hydrogen sulfide gas via the transsulfuration pathway (56). Unlike most of the other anti-aging diets including CR, mice restricted for particular amino acids appear to actually eat more food than control fed animals but fail to gain weight (57, 58)."