Methionine
The gateway to methylation. Methionine is the essential amino acid that becomes SAMe - the universal methyl donor your body uses for 200+ reactions. Too little and methylation stalls. Too much and you age faster.
The Methionine Cycle
Methionine
Essential amino acid from diet (eggs, meat, fish)
SAMe
Methionine + ATP. Universal methyl donor for 200+ reactions
SAH → Homocysteine
After donating methyl group. Must be recycled or cleared
Recycle or Exit
Back to methionine (B12, folate) or to cysteine (B6)
What Methionine Becomes
SAMe (S-Adenosylmethionine)
The "activated" form. Donates methyl groups for DNA, neurotransmitters, hormones, creatine, and more.
Cysteine
Via homocysteine transsulfuration. Rate-limiting for glutathione synthesis. Requires B6.
Taurine
Made from cysteine. Important for bile acids, heart, brain, and electrolyte balance.
Glutathione
Via cysteine. Master antioxidant and detoxifier. Methionine is upstream of glutathione.
Creatine
SAMe methylates guanidinoacetate to form creatine. Uses ~40% of SAMe methyl groups.
Polyamines
Spermidine, spermine from decarboxylated SAMe. Important for cell growth.
The Methionine Balance Problem
Too Much Methionine
- •Elevated homocysteine (cardiovascular risk)
- •Accelerated aging (methionine restriction extends lifespan in animals)
- •Increased oxidative stress
- •Imbalance with glycine (modern muscle-meat diets)
Too Little Methionine
- •Impaired methylation (can't make SAMe)
- •Low glutathione (via low cysteine)
- •Poor protein synthesis (start codon)
- •Muscle wasting, weakness
The solution: Moderate methionine intake with adequate B vitamins (especially B12, folate, B6) and glycine to balance the ratio. Ancestral diets included glycine-rich connective tissue that balanced muscle meat's methionine.
Food Sources
Highest Sources
Eggs (especially yolks), fish, meat, poultry, dairy. Animal proteins are rich in methionine.
Plant Sources
Brazil nuts, sesame seeds, spirulina, soy. Plant proteins are generally lower in methionine.
Balance With
Glycine-rich foods: bone broth, collagen, gelatin. These balance the methionine in muscle meat.
Cofactor Requirements
ATP
Combines with methionine to form SAMe. Energy required.
Vitamin B12
Recycles homocysteine back to methionine via methionine synthase.
Folate (5-MTHF)
Provides methyl group for homocysteine remethylation.
Vitamin B6
Required for transsulfuration (homocysteine → cysteine).
Metabolic Connections
SAMe
Methionine + ATP creates the universal methyl donor
Homocysteine
Formed when SAMe donates its methyl group
Cysteine
Made from homocysteine via transsulfuration
Taurine
Downstream product via cysteine
Glycine
Balances methionine; ancestral diets had equal amounts
Vitamin B12
Required to recycle homocysteine back to methionine