Cystine Introduction

Cystine is a nonessential, sulfur-containing amino acid that is formed from the oxidation of the amino acid cysteine. This oxidation process is quite complex, beginning with methionine and ending with cystine.

This nonessential amino acid is concentrated in various protein structures located throughout the body. It is an important constituent of connective and skeletal tissue, digestive enzymes (chromotrypsinogen A, papain, and trypsinogen), insulin, and hair keratin. Cystine, in association with N-acetylcysteine (NAC), can be used in place of L-cysteine, and may prevent side effects associated with exposure to certain types of radiation. [1] Cystine may also aid in the body’s natural detoxification processes.

Glutathione is a major antioxidant compound found in living animal and plant tissue. Cystine increases glutathione levels in major organs and bone marrow, providing the body with an anti-aging mechanism. This has proved especially useful in the reduction and accrual of age spots.

Cystine Food Sources

Nearly all foods contain sufficient amounts of cystine. Viable sources of cystine include whole grains, soybeans, whey, beans, dairy products, eggs, meat, nuts, and seafood. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of cystine contained.

Cereal Grains and Pasta
mg/100g Food Name
575.9 Oat bran, raw
540.1 Macaroni, protein-fortified, dry, enriched, (n x 5.70)

Breakfast Cereals
mg/100g Food Name
575.9 Cereals ready-to-eat, wheat germ, toasted, plain

Vegetables and Vegetable Products
mg/100g Food Name
662.1 Seaweed, spirulina, dried

Nut and Seed Products
mg/100g Food Name
952.1 Seeds, sunflower seed flour, partially defatted
855 Seeds, cottonseed kernels, roasted (glandless)
814 Seeds, sesame flour, partially defatted
685 Seeds, safflower seed meal, partially defatted
621.1 Seeds, sesame flour, high-fat

Legumes and Legume Products
mg/100g Food Name
1150 Soy protein isolate, Protein Technologies International, supro
1100 Soy protein isolate, Protein Technologies International, ProPlus
1046 Soy protein isolate
1046 Soy protein isolate, potassium type
1046 Soy protein isolate, potassium type, crude protein basis
886 Soy protein concentrate, produced by alcohol extraction
886 Soy protein concentrate, produced by acid wash
886 Soy protein concentrate, crude protein basis (N x 6.25), produced by acid wash
757 Soy flour, defatted
757 Soy flour, defatted, crude protein basis (N x 6.25)
750 Soy flour, low-fat
750 Soy flour, low-fat, crude protein basis (N x 6.25)
723.9 Soy meal, defatted, raw
668.9 Peanut flour, defatted
662.9 Tofu, dried-frozen (koyadofu)
662.9 Tofu, dried-frozen (koyadofu), prepared with calcium sulfate
638.1 Soybeans, mature seeds, dry roasted
627.1 Meat extender
588.1 Soybeans, mature seeds, raw
566.9 Soybeans, mature seeds, roasted, salted
566.9 Soybeans, mature seeds, roasted, no salt added
561 Soy flour, full-fat, roasted
555.9 Soy flour, full-fat, raw
545 Winged beans, mature seeds, raw

Finfish and Shellfish Products
mg/100g Food Name
673 Fish, cod, Atlantic, dried and salted

Beef Products
mg/100g Food Name
727 Beef, variety meats and by-products, spleen, cooked, braised

Pork Products
mg/100g Food Name
557 Pork, fresh, variety meats and by-products, kidneys, cooked, braised

Dairy and Egg Products
mg/100g Food Name
2102 Egg, white, dried
1099 Egg, whole, dried
613.9 Egg, yolk, dried

Spices and Herbs
mg/100g Food Name
582.1 Spices, mustard seed, yellow


Cystine Uses

Information regarding cystine use in human physiology remains limited. Cystine is an effective detoxification agent, protecting the body against free radicals in the environment. The effects of assorted oxidants contained in alcohol and cigarette smoke may be lessened as a result of the dietary supplementation of cystine. It may also prove useful in diminishing the effects of a “hang over” caused by excessive alcohol consumption, as well as preventing liver and even brain damage.

Because cystine contains anti-oxidative properties, it may increase immunity by aiding in white blood-cell activity.

Its most practical use may be in its ability to thwart obesity. Cystine is integral in the production of insulin in the pancreas gland. Taken in conjunction with vitamin C, cystine may further assist the body in its assimilation of sugars and starches. Cystine may neutralize excess insulin production, thereby eliminating unwanted fat production and deposition.

Other bodily functions are equally dependant upon this amino acid. Cysteine is fundamental in providing proper functioning of the largest organ in the human body - the skin. The flexibility and texture of skin are directly influenced by adequate cystine intake. Cystine also aids in the formation of carotene which is an agent of hair growth and health. The health of collagen, a connective tissue protein, is also dependant upon cystine.

Cystine Dosages

Because cystine is considered a nonessential amino acid, a Recommended Daily Allowance (RDA) has not been established. The U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight - equaling 0.8 grams of protein per kilogram of bodyweight.

Cystine Toxicities and Deficiencies

Cystine Deficiency

A deficiency of cystine is very unlikely, however, certain chronic diseases inhibit the formation of cysteine from methionine and may result in a cystine deficiency. Choline, a key component of phospholipids, may assist individuals suffering from the hereditary disorder, Cystinuria; where vast amounts of cystine are lost in urine.

Cystine Toxicity

Prolonged and excessive intakes of cystine may result in the formation of cystine kidney stones. To eliminate this possibility, it is recommended that adequate amounts of ascorbic acid are consumed in concurrence with cystine.

Individuals suffering from diabetes mellitus should not use supplemental cystine due to its ability to inactivate certain disulphidedbrids of insulin, which are critical in determining this hormone’s structure.


1. Balch, Phyllis A., James F. “Amino Acids.” Prescription for Nutritional Healing. Ed. Amy C. Tecklenberg. New York, NY: Penguin Putnam Inc., 3rd Ed. 2000. 42-53.

2. Nutrition Data. “999 Foods; Highest in Cystine.” (2004)

3. Zest for life information page. “RDA of amino acids.” (1999-2003) (14 Sept. 2004).


Cystine Products