Methionine & Sulfur Amino Acid Restriction
Limiting methionine and cysteine extends lifespan in animals and lowers IGF-1; intermittent versions may spare muscle.
Summary
She explains that animal studies suggest restricting methionine, rather than calories alone, drives much of calorie restriction's longevity benefit (e.g., a 45% increase in maximal lifespan in mice), but long-term low-protein eating raises concerns about muscle, bone and frailty. A 2024 mouse study found intermittent restriction (3 days a week) gave similar IGF-1 benefits with less bone and lean-mass loss. Her 2025 post adds that cysteine appears to be the key sulfur amino acid, and small human trials of sulfur amino acid restriction reduced weight, IGF-1, insulin and leptin and raised FGF21. She connects methionine to the methylation cycle, homocysteine and B vitamins; related roundups on valine and BCAA restriction show other amino acids also affect longevity in mice.
"I'm going to give it a try with eating low protein - avoiding the sulfur amino acids - for a couple of days a week."From Sulfur Amino Acid Restriction for Longevity and Weight Loss
The evidence
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Human trial
A 2024 clinical trial in 20 adults found 4 weeks of a sulfur amino acid restricted diet decreased body weight, cholesterol, uric acid, leptin, insulin and IGF-1 and increased FGF21, with fewer changes from methionine restriction alone.
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Human trial
In a clinical trial in healthy adults, a sulfur amino acid restricted diet reduced weight 20% more than an equal-calorie diet high in sulfur amino acids.
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Human obs.
In older adults, methionine intake was positively associated with risk of mild cognitive impairment; in the same paper, methionine restriction reduced amyloid-beta in an Alzheimer's mouse model.
Read the study Discussed in Intermittent Methionine Restriction -
Animal
In a year-long animal study, a low-methionine diet 3 days a week gave IGF-1 changes similar to full methionine restriction with less negative impact on bone and lean mass.
Read the study Discussed in Intermittent Methionine Restriction -
Animal
A methionine-restricted diet increased maximal lifespan by 45% in mice.
Read the study Discussed in Intermittent Methionine Restriction -
Animal
In mice unable to make cysteine, cysteine restriction caused 30% weight loss in 7 days (fat, not muscle) and raised FGF21; the authors conclude cysteine is key to the benefits of sulfur amino acid restriction.
Doses used in studies
Amounts reported in the research, not dosing recommendations.
| Dose | Context |
|---|---|
| Low-methionine diet 3 days/week, standard diet 4 days/week, for one year | Animal study of intermittent vs. full methionine restriction |
| Sulfur amino acid restricted diet for 4 weeks | Clinical trial in 20 adults |
Cautions
- Long-term methionine restriction amounts to a low-protein diet, raising concerns about muscle loss, frailty and bone health (osteoporosis) in aging.
- Long-term methionine restriction can bring Epstein-Barr virus out of latency; implications for immunocompromised people are unknown.
- Unclear whether long-term cysteine restriction is a good idea, or at what point it causes muscle breakdown or affects bone.
- In mice, adding N-acetylcysteine to a SAAR diet abrogated the positive effects on lipids and weight loss.