For methionine restriction extending lifespan in mice:
Miller et al. (2005) published in Aging Cell showing that methionine restriction (reducing dietary methionine to ~20% of normal) extended median and maximum lifespan in mice by approximately 30%. This pioneering study established methionine restriction as a powerful dietary intervention.
Methionine‐deficient diet extends mouse lifespan, slows immune and lens aging, alters glucose, T4, IGF‐I and insulin levels, and increases hepatocyte MIF levels and stress resistance - PMC
For glycine supplementation extending lifespan:
Miller et al. (2019) in Aging Cell reported that within the ITP: 8% glycine supplementation in mice extended median lifespan by 5.8% and maximum lifespan by 4.4% - while this is less than the ~30% I mentioned earlier, it’s significant for a single amino acid supplement.
Methionine restriction has consistently shown 20-40% lifespan extension across multiple studies, the glycine supplementation data is still emerging. The strongest evidence for glycine’s benefits seems to come from its ability to restore normal lifespan in mice fed high-methionine diets and its consistent improvement in healthspan markers.
Glycine supplementation operates through complementary mechanisms to methionine restriction by improving the clearance of methionine metabolites, leading to similar metabolic benefits. However, the magnitude of lifespan extension with glycine alone appears to be more modest than with methionine restriction based on current evidence.
Restricting methionine over many years is not something I can consider. Adding glycine is easier but might be less rewarding. But I already add glycine to my diet. Converting the human dose of glycine at in a diet of 6% glycine for a 75 kg human can be calculated as (Using AI):
- Determine total daily caloric intake for a 75 kg human,.
For moderate activity: 30-35 calories per kg body weight
For a 75 kg person: 75 × 30-35 = 2,250-2,625 calories per day
Let’s use 2,400 calories as our working value
- Calculate 6% of total calories
6% of 2,400 calories = 0.06 × 2,400 = 144 calories from glycine
- Convert calories to grams of glycine
Glycine provides 4 calories per gram (like all amino acids)
Therefore: 144 calories ÷ 4 calories/gram = 36 grams of glycine per day
Compare to other dosing approaches
This calculation gives us 36 grams of glycine per day for a 75 kg human to match 6% of caloric intake used in animal studies. This is notably higher than what’s typically used in human research.
Why the discrepancy? There are several key considerations:
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Caloric density differences: Mice typically consume relatively more calories per unit of body weight than humans (they have higher metabolic rates)
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Bioavailability: Glycine absorption efficiency may differ between species
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Metabolic scaling: the body surface area scaling factor means that doses don’t translate directly
Our calculation showing 36 grams, but human studies have shown benefits with much lower doses:
Clinical studies: 3-15 grams per day
Metabolic benefits: Often seen at 10-12 grams per day
Upper practical limit: Most researchers don’t go above 20 grams per day
The calculation suggests 36 grams to precisely match the animal study proportion, the practical human dose would be less:
5-10 grams per day, if that is ok then maybe increase to 15-20 grams per day if desired and well-tolerated. Maybe split into 2-3 doses throughout the day.
This discrepancy highlights why direct translation from animal studies to human doses often requires adjustment. The key principle is that glycine appears to work by correcting the methionine ratio in the diet, and humans typically need less supplementation to achieve this balance than would be predicted by direct caloric percentage conversion.
