[1] As of 2016, the position of the Academy of Nutrition and Dietetics is that protein from a variety of plant foods eaten during the course of a day supplies enough of all essential amino acids when caloric requirements are met.
Though it is undisputed that diverse foods can be thoughtfully combined to make a more nutritious meal, a general consensus has emerged among nutrition scientists and writers contrary the earlier dogma.
Studies on essential amino acid contents in plant proteins have shown that vegetarians and vegans typically do not need to complement plant proteins in each meal to reach the desired level of essential amino acids as long as their diets are varied and caloric requirements are met.
Similarly, human nutrition is subject to Liebig's law of the minimum: The lowest level of one of the essential amino acids will be the limiting factor in metabolism.
In the above examples, neither whole rice nor canned chickpeas have sufficient amounts of all required amino acids when used as the only source of 46.2 g of daily protein.
The first biochemist to enter the field was Karl Heinrich Ritthausen, a student of Justus von Liebig.
Thus Yale University was the early center of protein nutrition, where William Cumming Rose was a student.
[11] In 1971, Frances Moore Lappé published Diet for a Small Planet, which explained how essential amino acids might be obtained from complementary sources in vegetarian nutrition.
The book became a bestseller : Lappé wrote: In 1975, both Vogue and American Journal of Nursing carried articles describing the principles and practice of protein combining.
[5] In 2009, the American Dietetic Association wrote: The American Heart Association now states: Some institutions use the Protein Digestibility Corrected Amino Acid Score to assess diets without consideration of protein combining and hence find the use of combinations to be a challenge to their methodology.