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What is methionine?

Methionine is an essential amino acid [1]. In foods, methionine is incorporated into proteins.

Methionine abbreviation (symbol): Met

Methionine Functions in the Human Body

Methionine is [1]:

  • A building block of proteins
  • S glucogenic amino acid — it can be converted into glucose [3]
  • A source of sulfur
  • precursor of carnitine (a substance that helps to convert fats into energy)
  • A substance that helps the liver to efficiently process fats

Methionine Rich Foods

  • ANIMAL FOODS: beef, pork, poultry, fish, crabs, mollusks, cheese, egg white [2]
  • PLANT FOODS (>50 mg/100 g food): whole grains, cornmeal, nuts, seeds [2]

Foods low in methionine: fruits, lentils, green leafy vegetables [2]


Hypermethioninemia is a rare hereditary (usually autosomal recessive) disorder with increased blood levels of methionine; it may occur together with other genetic metabolic disorders, such as homocystinuria, tyrosinemia and galactosemia [7]. Symptoms and complications may include intellectual disabilities, delays in standing or walking, muscle weakness, unusual facial features and a boiled cabbage-smelling breath, sweat or urine [7].

Hypermethioninemia can also occur in infants fed with diets high in methionine [7].

L-Methionine Supplements

Nonprescription (over-the-counter) L-methionine oral supplements are available.

L-Methionine Benefits

There is INSUFFICIENT EVIDENCE about the effectiveness of L-methionine supplements in the prevention or treatment of alcoholism, allergies, asthma, colorectal cancer, Parkinson’s disease, radiation side effects, schizophrenia or drug withdrawal symptoms, or in improving liver function [4].

L-methionine supplements are POSSIBLY INEFFECTIVE in the prevention of hot flashes in menopausal women [6].

Methionine Safety: Side Effects, Toxicity

Methionine in recommended doses is POSSIBLY SAFE for most adults and children [4].

Side effects of methionine supplements may include nausea, vomiting and drowsiness [5]. Allergic reaction to l-methionine are possible; symptoms may include itchy skin, rash, difficulty breathing, swelling of the face, lips, or tongue.

During Pregnancy

Not enough studies about safety of methionine supplements during pregnancy and breastfeeding have been performed, so women in these periods should better avoid them [4].

Who may need to avoid methionine?

Individuals with the following conditions may need to avoid methionine supplements or foods high in methionine [4]:

  • Homocystinuria, tyrosinemia and galactosemia
  • Acidosis
  • Liver cirrhosis
  • Schizophrenia
  • Methylenetetrahydrofolate reductase (MTHFR) deficiency

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