On the “complete protein” concept, by a famous popularizer of plant-based protein-combining[0]
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There is no need to combine foods at individual meals.
“In 1971 I stressed protein complementarity because I assumed that the only way to get enough protein ... was to create a protein as usable by the body as animal protein. In combating the myth that meat is the only way to get high-quality protein, I reinforced another myth. I gave the impression that in order to get enough protein without meat, considerable care was needed in choosing foods. Actually, it is much easier than I thought. With three important exceptions, there is little danger of protein deficiency in a plant food diet.”
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[0] https://en.wikipedia.org/wiki/Diet_for_a_Small_Planet
Edit: adjust description of what Lappé was popularizer of