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What is Cysteine?

Cysteine is a semi-essential amino acid, a building block of proteins, vital for various bodily functions. It's known for its sulfur content, contributing to antioxidant properties and supporting metabolic processes. Intriguingly, cysteine also plays a role in skin and hair health. Curious about how this amino acid impacts your well-being? Discover its multifaceted roles through vivid imagery in our comprehensive guide. What will you learn next?
Ann Olson
Ann Olson

Cysteine is a sulfur-containing non-essential amino acid commonly found in high-protein meat products. It is synthesized by the body if there is a substantial amount of methionine, another non-essential amino acid, available. It has a chemical structure similar to that of selenocysteine, with the difference being that selenocysteine contains a selenium atom instead of a sulfur atom.

As a nutritional supplement, this substance reportedly has several benefits. When consumed, it is converted into glutathione, an antioxidant. Antioxidants have been reported to have numerous health benefits for humans, including the reduction of free radical damage. Scientists believe that free radicals damage the deoxyribonucleic acid (DNA) and membranes of cells, which can lead to premature aging, heart disease and cancer. It can be converted into a powerful antioxidant that can prevent this damage, which might lower a person's risk for heart disease and certain types of cancers.

Cysteine is an amino acid found in meat products, like pork.
Cysteine is an amino acid found in meat products, like pork.

When given intravenously, cysteine also might prevent or reduce liver or kidney damage caused by an acetaminophen overdose. It also might reduce the symptoms of influenza, acute respiratory distress syndrome (ARDS), asthma, cystic fibrosis, emphysema and Sjogren's syndrome. It also has a preventative effect against colon cancer and cataracts. People recovering from cocaine addiction, severe schizophrenia episodes or gambling addiction also might benefit from taking it. It also can help women with polycystic ovary disease become pregnant, because of its ability to improve their fertility rate.

Broccoli contains high amounts of cysteine, which can be very helpful for the body.
Broccoli contains high amounts of cysteine, which can be very helpful for the body.

It occurs naturally in some dietary sources, such as meat and vegetable products. High-protein foods, such as pork, sausage, chicken, turkey, eggs, whey protein and yogurt, contain a high amount of this amino acid. Some vegetables, such as Brussels sprouts, broccoli, garlic and red peppers also contain a high amount of it.

It is available in supplement form as N-acetyl-L-cysteine (NAC). When consumed, the body converts this into cysteine. The NAC form of it is specifically used to prevent side effects caused by some drugs. It also is used to break down mucus in the body and might reduce the severity of bronchitis and chronic obstructive pulmonary disease (COPD), which are worsened by mucus buildup.

Cysteine can help prevent colon cancer.
Cysteine can help prevent colon cancer.

This amino acid is available in spray, liquid, topical ointment, powder or capsule form. Although NAC might prevent liver and kidney damage, it can raise homocysteine levels, which can increase a person's risk for heart disease. NAC also might cause vomiting, diarrhea and nausea. Some forms of this amino acid, including D-cysteine and 5-methyl cysteine, are potentially toxic.

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Discussion Comments


@saraq90 - You might even talk your family member into lifting weights to get the added bonus of muscle building with the whey protein, and a little exercise is always good for the brain which can hopefully improve his mood a little (if he has days where he is struggling)! But I am biased; I lift weights and feel it makes me more energetic.

Anyway, my best suggestion to mix with whey protein is sweet yogurt like vanilla yogurt (do not go with plain yogurt it does not cover up the somewhat chalky taste of the whey protein enough) and fruit to make a smoothie! When I want something even a little sweeter I might try a little sherbet in with the yogurt in fruit.

Fruits that I have tried in the smoothies are strawberries, blueberries, and bananas. I usually stuck with those fruits because you could buy the strawberries and blueberries frozen so they would not spoil and bananas just tasted so well in them!


I was worried when I first started reading the article and saw that this cystine was in high protein meat products (as I have been a vegetarian for a year or two now), but then I continued to read and see eggs and yogurt also contain it.

Someone in my family has schizophrenia and while on medications and living fairly normal life; he is always looking for things to keep him healthy and stop him from having what he calls his "breaks". He is a very sweet man and tries very hard at managing a very difficult disease that he has had for almost 10 years now.

I will have to tell him to look into this, especially since it is easy to add into your diet. I thought if my family member with schizophrenia needed a larger dose to get some of the good effects I would suggest to him to try Whey Protein. I had tried it when I was lifting weights more but I could never get it to taste very good at all.

Any suggestions on what to mix with whey protein?

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    • Cysteine is an amino acid found in meat products, like pork.
      By: evgenyb
      Cysteine is an amino acid found in meat products, like pork.
    • Broccoli contains high amounts of cysteine, which can be very helpful for the body.
      By: PhotoEd
      Broccoli contains high amounts of cysteine, which can be very helpful for the body.
    • Cysteine can help prevent colon cancer.
      Cysteine can help prevent colon cancer.
    • Yogurt contains a high amount of cysteine.
      By: nenetus
      Yogurt contains a high amount of cysteine.