> Since this was also a noninterventional study, two possibilities for interpretation of the findings were either that a high cysteine somehow promotes obesity or that obesity influences cysteine turnover, thereby raising plasma tCys.

https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2011.93

> Pepsin forms three between the sulfur atoms of cysteine residues in the peptide chain which hold important roles in the folding of the protein and stabilizing the two domains

[1] https://en.wikipedia.org/wiki/Pepsin

[2] https://biology.kenyon.edu/BMB/jsmol2021/Cat_Marko/index.htm...

I could be wrong, but I doubt it. Amino acid depletion sounds way more likely to be due to some kind of disruption in homeostasis rather than dietary intake.