Cysteine is a sulphur-containing, semi-essential amino acid that the body can partly make itself from the amino acid methionine. Among other things, it plays a role in building protein structures, as the sulphur group it contains allows bonds between protein chains, for example in hair and nails.
Cysteine is also a building block of the body's own antioxidant glutathione, which is involved in protecting cells from oxidative stress. In food, cysteine is found in protein-rich foods such as meat, eggs and dairy products, and in smaller amounts in pulses and cereals.
Relevance for nutrition and sport
For physically active people, cysteine is of interest mainly in connection with the body's antioxidant protection system, as intensive training can temporarily increase oxidative stress. A separate cysteine supplement is, however, not necessary for most people with an adequate total protein intake.
With a balanced, protein-rich diet, the cysteine requirement is generally well covered, as the body can also partly synthesise it itself. The page amino acids explains more about amino acids and their role in nutrition and sport. If an adequate total protein intake is part of the daily diet, looking at individual amino acids in isolation is usually of secondary importance.
