There are 20+ sources here, including a little story from the woman who started it.
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Protein combining (also protein complementing) is the theory that vegetarians, particularly vegans, must eat certain complementary foods like beans and rice together in the same meal,
I did my own search on "complete protein myth". Yes, there are tons of hits. Guess what. They are all pro-vegetarian sites, and they all follow the same chain of logic back to Frances Moore Lappé.
Just because her protein combining theory ( on the need to combine essential amino acids in the same meal) was wrong and she mostly retracted it, that doesn't affect the complete protein concept's validity.
"Protein combining" theory ≠ "Need to eat all essential amino" acids theory.
Seems to me they are just replacing one myth with an (anti-) myth of their own.
Body cells are made using amino acids, humans can't create the essential amino acids, so they must be eaten from one source or another. Meat - all meat - contains all the essential amino acids in appropriate ratios for the body's needs. Most vegetables do not. These facts don't seem to be disputed.
Those sites claiming that there is a myth surrounding complete protein still accept that you do need all the essential amino acids. They say you can get that from a balanced diet based on vegetables. Can you spot the flaw in that line of reasoning?
Of course you can get all the essential amino acids from (any) truly balanced diet, because it wouldn't be a balanced diet if it was lacking in essential amino acids.