Protein combining

Protein combining or protein complementing is a dietary theory for protein nutrition that purports to optimize the biological value of protein intake. According to the theory, individual vegetarian and vegan foods may provide an insufficient amount of some essential amino acids, making protein combining with multiple complementary foods necessary to obtain a meal with "complete protein". All plant foods contain all 20 amino acids including the 9 essential amino acids in varying amounts, but some may be present in such small amounts that an unrealisticly large amount of the food needs to be consumed to meet requirements.

Protein combining was historically promoted as a method of compensating for supposed protein deficiencies in most vegetables as foods (e.g., rice and beans), found in limiting percentages revealed in their respective amino acid profiles. In this dogma of the 1970s, each meal needs to be combined to form complete proteins. Though it is undisputed that diverse foods can be thoughtfully combined to make a more nutritious meal, studies on essential amino acid contents in plant proteins have shown that careful combination in each meal is not required for vegetarians and vegans to reach the desired level of essential amino acids as long as their diets are varied and daily caloric requirements are met. In other words, combination can happen over a longer course of time.