Your body needs a total of 20 amino acids to function regularly, although only nine of these have to come from dietary sources. Grains contain all of these "essential" amino acids in varying concentrations. As such, you can hypothetically meet all of your daily essential amino acid needs with grains. However, as most grains lack in one or more of these compounds, you would need to eat an excessively large number of servings each day to do so.
Grains are generally very poor sources of lysine. To meet your body's needs for this essential amino acid, you would need to eat between 15 and 30 servings of most grains every day. Buckwheat, corn and oatmeal all contain slightly higher concentrations of lysine than most other grains. However, even these grains meet your daily lysine needs only at extreme amounts -- approximately 8 to 10 servings per day for a 140-pound person. Quinoa is the only grain that contains high concentrations of lysine, meeting your daily needs in 5.5 cups per day.
In contrast with their lysine content, most grains are good sources of methionine. For example, 4.5 or fewer 1-cup servings of quinoa, oatmeal or pasta is enough to meet a 140-pound person's daily methionine needs. Rice, corn, buckwheat, bread and flour tortillas all provide slightly less methionine, meeting your daily needs in six to eight servings per day. However, as other foods contribute to your daily intake of all essential amino acids, a few servings of grains can easily meet your daily methionine needs when part of a balanced diet.
Other Amino Acids
Most grains contain a relatively even balance of all essential amino acids except for lysine and methionine. Although not comparable to their low lysine content, grains generally lack in three essential amino acids: threonine, leucine and histidine. In contrast, grains are typically good sources of phenylalanine, tryptophan, valine and isoleucine. With the exception of corn and quinoa, you generally need to eat at least one additional serving of grains to obtain enough threonine, leucine and histidine after you have met your daily needs for phenylalanine, tryptophan, valine and isoleucine.
Grains and non-animal protein sources play complementary roles in meeting the essential amino acid needs of vegans and vegetarians. For example, soy products and other legumes are high in lysine and low in methionine, while grains are generally high in methionine and low in lysine. As such, the registered dietitians at Vegan Health suggest that you mix legumes and grains at each meal to ensure that you meet your essential amino acid needs. However, they point out that this process of carefully combining plant proteins is not necessary. As your liver is capable of storing essential amino acids, you need only to eat a varied, plant-based diet that regularly includes grains and legumes to obtain adequate amounts of these important compounds.
- Nutrition Almanac, 6th Edition; John D. Kirschmann and Nutrition Search, Inc.
- The Dietitian's Guide to Vegetarian Diets: Issues and Applications, 3rd Edition; Reed Mangels, Ph.D., R.D., et al.
- Vegan Health: Protein
- Quinoa image by bbroianigo from Fotolia.com