Here's a recent human trial that put obese people on a 8 week low methionine, low cysteine diet. The results are relatively unimpressive. Not sure why . Maybe the amount of M+C was too high (2g/day)?
"Both groups lost weight during the intervention. On average, the SAAR group lost 1.14 kg more body weight compared to controls after 8 weeks (β 95% CI − 1.14 (− 2.04, − 0.25) kg, p = 0.013). No conclusive differences between groups were observed for body fat %."
https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-023-04833-w
On the other hand here is a human study where a similar amount of M+C was shown to be beneficial. The lowest amount came down to 1500-2000mg of cysteine+methionine per day.
Major takeaway for me is: cysteine does matter.
The weight loss in the group lowest in cysteine was 3 times as much as in the group lowest in methionine.
Overall a good study design, which kind of corroborates the animal studies, showing that weight loss seems to be dependent on low cysteine, but only low methionine has some benefits as well.
Also the only diet that increased body temp significantly was the diet lowest in cysteine. The low methionine diets were ineffective or even slightly reduced body temp.
https://www.sciencedirect.com/science/article/pii/S1279770723003184#fig1