Individuals who are vegan or vegetarian will need to include in their diet a diverse range of plant protein sources to obtain adequate amounts of all essential amino acids. Most vegetarian sources of protein lack one or two essential amino acids. However, an assorted range of vegetarian proteins can ensure that essential amino acids lacking in one food source are provided by another, such as combining rice and beans. This is called mutual supplementation. It may be helpful to reinforce the importance of a varied and balanced diet for health and performance and for adequate protein intake.
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Grains, legumes, nuts, seeds, and vegetables are all considered to be incomplete sources of protein as they contain some but not all of the essential amino acids. However, they differ in their composition. For example, beans and vegetables are limited in methionine, nuts and seeds are limited in lysine, corn is limited in both tryptophan and lysine, and grains are limited in lysine and threonine.
Eating a balanced mix of all these sources can help to ensure that all essential amino acids are provided in a vegetarian diet. Note that complementary proteins do not have to be eaten at the same meal; it is sufficient if they are eaten over the course of the same day for mutual supplementation.