The health of hair, skin and nails depends on getting enough of the amino acid cysteine. You also need cysteine to produce the powerful antioxidant glutathione. Healthy people can synthesize what they need as long as they get adequate methionine, the essential amino acid from which cysteine is derived. However, stress or sickness may leave the body unable to produce enough cysteine. In these cases, a cysteine-rich diet can fulfill the requirement. Cysteine can exist naturally in foods as cystine, a compound metabolized to yield two cysteine molecules.
The U.S. Department of Agriculture lists the food content of cystine, not cysteine, in the amino acid section of their National Nutrient Database. According to their information, one of the richest sources of cystine -- and, once broken down in the body, cysteine -- is turkey breast meat. One whole roasted turkey breast contains 2.4 grams of cystine, while a single 3-ounce serving has 0.24 grams. Other types of poultry, including goose, chicken and pigeons, are also high in cystine.
Raw soybeans contain 1.2 grams of cystine in each cup. Roasted, unsalted soybeans have nearly 1 gram per cup and can serve as a cholesterol-free, high-cysteine snack. Defatted soy flour has approximately 0.8 grams in every cup. Use soy flour as a fiber- and protein-rich, virtually fat-free addition to rye or wheat flour in recipes for baked goods like cookies, yeast breads or quick breads. Substituting 10 to 30 percent of regular flour with soy flour is a good rule, advises the Soyfoods Association of North America.
Eggs, whether fresh, dried, whole or separated into whites and yolks, are a good source of cystine. Glucose-reduced dried egg white powder contains 2.2 grams of cystine in each cup. A 2-teaspoon serving of the powder reconstituted with water to act as a substitute for one egg white supplies about 0.1 grams of cystine. One large, whole hard-cooked egg contains 0.2 grams of the amino acid.
A cup of oats and a cup of uncooked couscous have about the same amount of cystine at 0.6 grams. Other cereal grains, such as hard red winter wheat, spelt, durum wheat, oat bran, triticale and barley, also have a high concentration of cystine per serving, ranging between 0.5 and 0.6 grams in each cup. Look for whole-grain versions of these cereals whenever possible, such as bread made with whole wheat flour instead of refined flour bread for more fiber, vitamins and minerals in addition to the cystine.