Cysteine
Cysteine is the sulfur-carrying amino acid the body uses to make glutathione and to lock hair and nails together. It is made from methionine, so it is not strictly essential, and food tables list it as cystine.
15 mg per kg of body weight a day, with methionine
1,050 mg of the two together for a 70 kg adult (WHO)
Upper limit · none set by the EU or the US
- Most per 100 g 0.57g Soy nuts
- Main sources Oats, seeds and nuts then eggs, meat and fish
- Made from Methionine plus serine, with vitamin B6
- Becomes Glutathione and taurine
Daily amount: WHO, FAO and UNU 2007 report, which gives methionine and cysteine as one figure. Food figures per 100 g from USDA FoodData Central, listed there as cystine, only for foods with a Caltide calorie page.
Foods High in Cysteine
Ranked per 100 g, with what a usual portion gives, limited to 3 foods per category. Foods with a Caltide calorie page link to it.
S
Soy nuts
0.54 g in 1 cup
0.57g / 100 g
S
Schnitzel (pork)
0.57 g in 1 piece
0.47g / 100 g
O
Oats
0.18 g in 1 bowl, dry
Nutrition facts
0.46g / 100 g
C
Caviar
0.072 g in 1 tablespoon
0.45g / 100 g
S
Sesame seeds
0.56 g in 1 cup
0.44g / 100 g
B
Bacon
Nutrition facts
0.42g / 100 g
C
Chia seeds
0.049 g in 1 tablespoon
Nutrition facts
0.41g / 100 g
S
Sunflower seeds
0.55 g in 1 cup
0.38g / 100 g
M
Mixed seeds
0.54 g in 1 cup
0.37g / 100 g
C
Couscous
0.62 g in 1 cup
0.36g / 100 g
C
Chicken tail
0.1 g in 1 tail
0.34g / 100 g
S
Soy nut butter
0.054 g in 1 tablespoon
0.34g / 100 g
What Is Cysteine?
Cysteine is one of two amino acids in protein that contain sulfur; the other is methionine. Its sulfur sits at the end of the side chain as a thiol group, which reacts readily, and that reactivity is the reason cysteine matters.
Cysteine vs. Cystine
When two cysteines meet, their sulfur atoms can join in a disulfide bond, and the pair is called cystine. The body converts between the two all the time. Food analysis measures both together and reports the result as cystine, which is why Caltide's food figures and Nutrition tab use that name.
What Cysteine Does in the Body
Makes glutathione. Glutathione is a small molecule of three amino acids, glutamate, cysteine and glycine, that cells use to neutralize reactive oxygen and to clear some drugs and toxins in the liver. Of the three, cysteine is usually the one in shortest supply, so it sets how much glutathione a cell can make.
Holds proteins in shape. Disulfide bonds act as cross-links that keep a folded protein in shape. Insulin, antibodies and keratin all depend on them, and keratin in hair, nails and the outer layer of skin is especially rich in cystine.
Becomes taurine. The liver turns cysteine into taurine, which the body uses for bile and in the heart, eyes and muscles.
Cysteine and Hair Perms
A perm shows what disulfide bonds do. The first lotion breaks the cystine bonds that hold hair keratin in its natural shape, the hair is set around a curler, and a second lotion lets new bonds form in the new position. Straightening treatments that use the same chemistry work the other way round.
How the Body Makes Cysteine and Which Foods Supply It
The liver builds cysteine by moving the sulfur from methionine onto serine, a step that needs vitamin B6. Because cysteine can be made this way, the WHO counts the two together. Every gram of cysteine you eat saves the body some methionine.
Grains are a better source than many people expect. In the Caltide food library, dry oats have 0.46 g of cystine per 100 g, ahead of boiled egg at 0.29 g, and a 40 g bowl gives about 180 mg. Cooked lentils have 0.12 g, which is why beans with grains is a classic pairing.
Compare more foods in the food library.
Who May Need More Cysteine
Preterm babies cannot yet make much cysteine from methionine, so it is treated as essential for them. Adults who eat very little protein, or whose diet is low in methionine as well, may also fall short.
Cysteine Supplements and Food Additives
Food protein is the main source, but supplements are a source too, and cysteine also reaches the diet as an additive.
NAC (N-acetylcysteine)
The most common cysteine supplement. In hospitals it is the antidote to acetaminophen (paracetamol) overdose and is used to loosen mucus. As a supplement it is studied for many uses with mixed results; see the NAC page for what the evidence shows.
L-Cysteine and L-Cystine
Sold on their own and in hair, skin and nail blends. Hair and nails are rich in cystine, but there is little good human evidence that extra cysteine makes them grow faster or stronger in people who eat enough protein.
Cysteine in Bread (E 920)
L-cysteine is an approved flour treatment agent in the EU, numbered E 920. It breaks some of the disulfide bonds in gluten so dough relaxes and machines can shape it faster.
Sources are listed at the end of this page. Not medical advice.
Tracking Cysteine in Caltide
- Logged automaticallyCaltide adds up the cystine in every food you log and in the supplements you tick off, and shows the total in the Nutrition tab.
- An amount, not a percentageThe WHO gives one figure for methionine and cysteine together, so Caltide shows how much cystine you ate without a share of a target.
Cysteine Sources and References
The figures and claims on this page are checked against these sources. Food amounts come from USDA FoodData Central.
Questions About Cysteine
No, it is conditionally essential. The body makes cysteine from the essential amino acid methionine, but preterm babies and people who eat too little methionine may not make enough.
Cystine is two cysteine molecules joined by a sulfur to sulfur bond. The body switches between the two easily, and food tables report both together as cystine.
The WHO, FAO and UNU 2007 report sets one figure for methionine and cysteine together: 15 mg per kilogram of body weight a day, about 1,050 mg for a 70 kg adult. Eating more cysteine lowers how much methionine is needed.
In the Caltide food library, soy nuts: 0.57 g of cystine per 100 g. Schnitzel (pork) (0.47 g) and Oats (0.46 g) come next.
A modest one. Beans and lentils are low in sulfur amino acids for the protein they carry: cooked lentils have 0.12 g of cystine per 100 g, against 0.46 g in dry oats. Grains and legumes together cover each other's gaps.
N-acetylcysteine, a form of cysteine with an acetyl group attached. Hospitals use it as the antidote to acetaminophen (paracetamol) overdose, because it helps the liver rebuild glutathione. It is also sold as a supplement.
L-cysteine is approved in the EU as a flour treatment agent, E 920. It softens gluten so industrial dough stretches more easily.
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