Proline is a nonessential amino that is found in all mammalian tissue. It exists as the main component of protein collagen, accounting for some 20% of this fibrous compound.  Proline assists in the binding and support of all connective tissue structures located throughout the body. Proline was first isolated from casein in 1901. Soon after, scientists discovered that proline is the only amino readily soluble in alcohol. This characteristic makes proline unique among all amino acids.
Synthesis of glutamic acid may provide the body with ample amounts of proline. Other amino acids partially responsible for the formation of proline include both glutamine and ornithine. Because proline exists in a nonessential classification, it does not require dietary sources for processing.
Proline is found with the highest concentrations in dairy products, eggs; various plant sources (e.g. wheat germ) also contain minimal amounts. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of proline contained:
|Cereal Grains and Pasta|
|2084||Macaroni, protein-fortified, dry, enriched, (n x 5.70)|
|2084||Spaghetti, protein-fortified, dry, enriched (n x 6.25)|
|Vegetables and Vegetable Products|
|2382||Seaweed, spirulina, dried|
|Nut and Seed Products|
|2494||Seeds, sunflower seed flour, partially defatted|
|2289||Seeds, sesame flour, low-fat|
|2125||Seeds, cottonseed flour, low fat (glandless)|
|2094||Seeds, cottonseed meal, partially defatted (glandless)|
|Legumes and Legume Products|
|2586||Tofu, dried-frozen (koyadofu)|
|2315||Soybeans, mature seeds, dry roasted|
|2304||Peanut flour, defatted|
|2135||Soybeans, mature seeds, raw|
|2060||Soybeans, mature seeds, roasted, salted|
|Finfish and Shellfish Products|
|2365||Mollusks, whelk, unspecified, cooked, moist heat|
|2221||Fish, cod, Atlantic, dried and salted|
|2254||Beef, cured, breakfast strips, cooked|
|2089||Beef, variety meats and by-products, lungs, cooked, braised|
|2118||Pork, cured, bacon, cooked, microwaved|
|2103||Pork, cured, bacon, cooked, pan-fried|
|Dairy and Egg Products|
|2549||Milk, dry, whole|
|2526||Cheese, low fat, cheddar or colby|
|2516||Cheese, pasteurized process, swiss, with di sodium phosphate|
|2498||Cheese, mozzarella, part skim milk|
|2403||Cheese, mexican, queso asadero|
|2351||Cheese, mozzarella, whole milk|
|2320||Cheese spread, pasteurized process, American|
|2253||Cheese, pasteurized process, American|
|2251||Cheese, pasteurized process, pimento|
|2249||Cheese, mexican, queso chihuahua|
|2241||Cheese, goat, soft type|
|2230||Cheese food, pasteurized process, swiss|
|2224||Cheese, mozzarella, whole milk, low moisture|
|2151||Cheese, mexican, queso anejo|
|2099||Dairy drink mix, chocolate, reduced calorie, with aspartame, powder|
Collagen is an fundamental nutrient in many processes involving tissues, including the promotion of healthy connective tissues. Being the major constituent of collagen, proline is integral in the production and maintenance of collagen as we age. Collagen would cease to exist without the inclusion of proline.
In union with ascorbic acid, proline is equally critical in maintaining the integrity of skin health and texture. Proline aids in the healing and maintenance of cartilage, and the strengthening of tendons, joints, and muscles as well.  Additionally, adequate levels of proline are essential for heart health.
Oxidation which effects cellular molecules (proteins and DNA), is often times combated with antioxidants. These antioxidants include the many phytochemicals found in plant foods. Recent study suggests that these antioxidants may be using an alternate energy producing pathway (pentose phosphate pathway), which directly involves the amino acid proline, to stimulate antioxidant response.  If current theory and research holds true, higher protein foods containing proline and proline precursors may ultimately assist in an increased antioxidant response within specific disease conditions.
Further clinical study is needed to determine the positives concerning dietary supplementation of proline, and the accompanying benefits it may provide in human physiology. Current theories are continually being put forth by nutritional scientists. Diseases such as diabetes, heart disease, arthritis, cognition diseases, and cancer, are all conditions of interest that may be properly influenced by additional intakes of proline.
Because proline is considered a nonessential amino acid, a Recommended Daily Allowance has not been established. However, it is recommended that ascorbic acid (vitamin C) be present in one’s diet to maximize the efficacy of proline.
In addition, 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.
Individuals receiving adequate amounts of protein in their diets are unlikely to develop a deficiency of this nutrient. Persons suffering from specific diseases, conditions, or infections may be at an increased risk for developing a deficiency state. Conditions that may contribute to amino acid deficiencies: chronic liver disease, sepsis (infection of the blood), and acute alcohol intake.
Of Note: A deficiency of proline oxidase, an enzyme that helps metabolize proline does exist. This condition is termed proline oxidase deficiency or Hyperprolinemia Type I (HP-I). This inborn error is characterized by abnormally high levels of proline in the blood. This elevation results from the absence of enzyme proline oxidase, which is essential for the normal breakdown (metabolism) of proline.
Toxicities of this amino acid are very rare. Excessive and prolonged intakes have not proven harmful in humans and little information exists concerning an acute overdose of proline. Extremely high doses of D-proline injected into the brain of chickens, however, caused death.
1. M. Watanabe, K. Sugimura, B. Yamanoha. Effect of acute deficiency of dietary proline on proline balance in the rat small intestine and liver. Journal of Animal Physiology and Animal Nutrition 1999 82:5 p. 294.
2. Nutrition Data. “999 Foods; Highest in Proline.” (2004) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
3. 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.
4. Wahiqvist, M.L. (2002) Asia Pacific J. Clin Nutrition, 2002;11(S): S759-S762)
5. Zest for life information page. “RDA of amino acids.” (1999-2003) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml (14 Sept. 2004).