What it does in the body
- Universal protein synthesis initiation (start codon)
- SAMe production for methylation reactions
- Glutathione and cysteine precursor (antioxidant defense)
- Liver detoxification support
- Creatine and carnitine biosynthesis
How much you need (Daily Value)
| Group | Recommended | Source |
|---|---|---|
| Adult male | 10.4mg/kg/day combined methionine + cysteine (~0.7g for 70kg) | WHO/FAO/UNU |
| Adult female | 10.4mg/kg/day (~0.6g for 60kg) | WHO/FAO/UNU |
| Pregnancy | 13mg/kg/day | WHO |
| Children | 17-28mg/kg/day depending on age | WHO |
| Older adults | 10.4mg/kg/day; ensure adequate B-vitamin cofactors | WHO |
Richest food sources
| Food | Amount | Where |
|---|---|---|
| Brazil nuts | 1.1g per 100g | south-america |
| Chicken breast (cooked) | 0.8g per 100g | global |
| Tuna (cooked) | 0.8g per 100g | global |
| Eggs (whole) | 0.4g per 100g | global |
| Beef (lean, cooked) | 0.7g per 100g | global |
| Sesame seeds | 0.6g per 100g | middle-east |
| Parmesan cheese | 0.9g per 100g | europe |
| Oats | 0.3g per 100g | global |
If you don't get enough
Mild: Fatigue, poor wound healing, mild liver steatosis
Moderate: Hair loss, brittle nails, fatty liver, impaired methylation (elevated homocysteine paradoxically)
Severe: Severe liver damage, growth retardation in children, neurological dysfunction
Time to onset: Metabolic changes within 1-2 weeks; clinical signs within 4-8 weeks
Too much
Upper limit: No established UL; intakes >5g/day may elevate homocysteine levels significantly
Elevated homocysteine, nausea, vomiting. Chronic excess linked to increased cardiovascular risk, potential tumor promotion
How well you absorb it
90-95% from animal sources; 75-85% from plant sources
Helped by: Folate, vitamin B6, and vitamin B12 (support methionine cycle and prevent homocysteine accumulation), Betaine
Hindered by: Alcohol (impairs methionine metabolism in liver), Folate deficiency (blocks homocysteine remethylation)
Cooking & storage
Relatively heat-stable. Normal cooking preserves methionine well. Alkaline cooking conditions (nixtamalization) can reduce methionine content slightly.
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