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.  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.
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|
|575.9||Oat bran, raw|
|540.1||Macaroni, protein-fortified, dry, enriched, (n x 5.70)|
|575.9||Cereals ready-to-eat, wheat germ, toasted, plain|
|Vegetables and Vegetable Products|
|662.1||Seaweed, spirulina, dried|
|Nut and Seed Products|
|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|
|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|
|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|
|673||Fish, cod, Atlantic, dried and salted|
|727||Beef, variety meats and by-products, spleen, cooked, braised|
|557||Pork, fresh, variety meats and by-products, kidneys, cooked, braised|
|Dairy and Egg Products|
|2102||Egg, white, dried|
|1099||Egg, whole, dried|
|613.9||Egg, yolk, dried|
|Spices and Herbs|
|582.1||Spices, mustard seed, yellow|
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.
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.
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.
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) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml (14 Sept. 2004).