In the rat study that added glycine to mimick methionine restriction, the longevity effects were seen at 8% and 12% glycine. Metabolic advantages were distinguishable at 12%. http://www.fasebj.or...bstracts/528.2
Seven-week-old male Fisher 344 rats were fed diets containing 0.43% Met/2.3% glycine (control fed; CF) or 0.43% Met/4%, 8% or 12% glycine until natural death. In 8% or 12% GS rats, median lifespan increased from 88 weeks (w) to 113 w, and maximum lifespan increased from 91 w to 119 w v CF. Body growth reduction was less dramatic, and not even significant in the 8% GS group. Dose-dependent reductions in several serum markers were also observed. Long-term (50 w) 12% GS resulted in reductions in mean (±SD) fasting glucose (158 ± 13 v 179 ± 46 mg/dL), insulin (0.7 ± 0.4 v 0.8 ± 0.3 ng/mL), IGF-1 (1082 ± 128 v 1407 ± 142 ng/mL) and triglyceride (113 ± 31 v 221 ± 56 mg/dL) levels compared to CF. Adiponectin, which increases with MR, did not change in GS after 12 w on diet.
... the problem is I don't have access to the full article, so I cannot say whether it was 12% weight of food or 12% of total calories. If anyone has any insight into this, or has access to the full article, please do update us on this information!
Lets say the methionine intake was .43% of calories, that would be 2.3g of methionine for a human eating 2000kcal, which is actually close to the average intake. Lets say the glycine intake was 12% of calories, that then would be 60g of methionine for a human eating 2000kcal, which is a ridiculous amount of glycine. If this is the case, and we don't need to make adjustments for species, then it's much more feasible to just restrict methionine and eat adequate glycine, than it is to supplement large amounts of glycine.
Edited by Adam Karlovsky, 17 January 2016 - 09:09 AM.