Methionine and cysteine
What it is and what it does
- Methionine is one of the nine essential amino acids, along with the others listed by MedlinePlus. (MedlinePlus Medical Encyclopedia (US National Library of Medicine): Amino acids (review date 1/21/2025))
- Of the two sulphur amino acids, methionine is essential; cysteine is made from methionine as it is broken down, so the body's cysteine depends on enough methionine. (WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935)
- Cysteine is listed as a conditionally essential amino acid: usually not essential, except in times of illness and stress. (MedlinePlus Medical Encyclopedia (US National Library of Medicine): Amino acids (review date 1/21/2025))
- Methionine's active form, S-adenosylmethionine (SAM), passes methyl groups on to many substances in cells (transmethylation). (Lopez MJ, Mohiuddin SS. Biochemistry, Essential Amino Acids. StatPearls [Internet], StatPearls Publishing (NCBI Bookshelf NBK557845; last update April 30, 2024))
- Folate is needed to turn homocysteine back into methionine, on the way to making S-adenosylmethionine, an important methyl donor. (NIH Office of Dietary Supplements. Folate Fact Sheet for Health Professionals (updated 2022-11-30))
- The body converts methionine onward to cysteine and to taurine; this conversion is regulated and appears functionally important. (WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935)
Why it matters
- The sulphur amino acids matter for body upkeep: their relative requirement for maintenance is probably higher than for growth. (WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935)
- In classic homocystinuria, an inherited disorder, homocysteine and methionine build up in the blood. (MedlinePlus Genetics: Homocystinuria (last updated May 1, 2023))
- WHO/FAO/UNU note that the sulphur amino acids (methionine and cysteine) may be toxic at high concentrations in the body; the body keeps their tissue levels very low. (WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935)
General information, not medical advice — for your own needs, ask a doctor or dietitian.
How much is needed
| Who | Amount | What the figure is | Whose figure |
|---|---|---|---|
| Adults | 22 mg per g protein | Recommended amino acid pattern (ICMR-NIN 2020) | ICMR-NIN 2020 (as printed in DGI 2024 Table 8.2) |
| Adults (mean requirement) | 15 mg/kg body weight/day | Average requirement | FAO/WHO/UNU 2007 (not an Indian value) |
| Older children, adolescents and adults | 23 mg per g protein | Scoring pattern for protein quality | FAO 2013 (not an Indian value) |
India’s own figure (ICMR-NIN 2020) comes first. Figures from other bodies are shown only where they help, and say whose they are.
Sources: ICMR-NIN. Dietary Guidelines for Indians 2024; WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935; FAO (2013). Dietary protein quality evaluation in human nutrition: report of an FAO Expert Consultation. FAO Food and Nutrition Paper 92
In every millet and pseudo-cereal, per 100 g raw
| Grain | Amount | Source |
|---|---|---|
| Methionine | ||
| Ragi (finger millet) | 2.74 g per 100 g protein | IFCT A010 |
| Kodo millet | 2.69 g per 100 g protein | IFCT A017 |
| Quinoa | 2.24 g per 100 g protein | IFCT A009 |
| Little millet | 2.21 g per 100 g protein | IFCT A016 |
| Bajra (pearl millet) | 2.11 g per 100 g protein | IFCT A003 |
| Rajgira (amaranth) | 1.95 g per 100 g protein | IFCT A002 |
| Jowar (sorghum) | 1.52 g per 100 g protein | IFCT A005 |
| Teff | 0.428 g | USDA FDC 169747 |
| Proso millet | 0.221 g | USDA FDC 169702 |
| Kuttu (buckwheat) | 0.172 g | USDA FDC 170286 |
| Cystine | ||
| Kodo millet | 1.92 g per 100 g protein | IFCT A017 |
| Quinoa | 1.85 g per 100 g protein | IFCT A009 |
| Little millet | 1.85 g per 100 g protein | IFCT A016 |
| Rajgira (amaranth) | 1.51 g per 100 g protein | IFCT A002 |
| Ragi (finger millet) | 1.48 g per 100 g protein | IFCT A010 |
| Bajra (pearl millet) | 1.23 g per 100 g protein | IFCT A003 |
| Jowar (sorghum) | 1.06 g per 100 g protein | IFCT A005 |
| Teff | 0.236 g | USDA FDC 169747 |
| Kuttu (buckwheat) | 0.229 g | USDA FDC 170286 |
| Proso millet | 0.212 g | USDA FDC 169702 |
Each grain has ONE source, named on its page: IFCT = Indian Food Composition Tables 2017 (ICMR-NIN) with its food code; USDA FDC; FAO WAFCT 2019; NIN 2007 via ICAR-IIMR. Values exactly as printed, not converted — tables differ in method, so compare within a source. Published values for the grain, not a laboratory test of our packs.
Absorption and food
- Cereals have less lysine than pulses but more of the sulphur amino acids, methionine and cysteine (ICMR-NIN). (ICMR-NIN. Dietary Guidelines for Indians 2024)
- In pulse (legume) proteins, methionine and cysteine are present only in marginal amounts. (WHO/FAO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. WHO Technical Report Series 935)
- ICMR-NIN's model vegetarian diet ('My Plate for the Day') provides 28.4 mg methionine + cysteine per g of protein, more than the 22 mg/g recommendation. (ICMR-NIN. Dietary Guidelines for Indians 2024)