The sources of L-cysteine can be divided into the following two categories:

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1、 In vivo synthesis

Methionine conversion: The human body can convert methionine (methionine) into L-cysteine through metabolic pathways.

Autologous synthesis ability: As a non essential amino acid, L-cysteine can be synthesized in small amounts in the body, but requires the participation of auxiliary factors such as vitamin B6.

2、 External acquisition

Natural food:

Foods rich in methionine, such as fish, eggs, seafood, etc., can promote the synthesis of L-cysteine in the body through intake.

Foods that directly contain L-cysteine: Some meats (such as chicken) and dairy products contain small amounts of L-cysteine