First of all, I do hope everyone considers this the right board for this topic. I considered "Not About Food," but protein in the diet would seem to be about food. The thread was about the need for protein in a vegetarian diet, and it was a tangent from a thread started by a vegetarian who's visiting Budapest.
Anyway, I'm no expert and welcome correction, but my understanding is that human beings need a supply of not merely protein but _complete_ protein in their diet every day. Complete proteins contain all amino acids necessary for human bodily functions. All animal meats (red, poultry, fish, seafood) and eggs provide complete protein, as do corn and beans in combination. I do not believe that any milk products (other than human breast milk, I suppose) provide complete protein, but I may be wrong. I'm pretty sure that no vegetable or fruit or grain product provides complete protein by itself, and that includes beans and bean products such as tofu. OK, experts, please correct me and fill in the blanks, as some of your fellow chowhounds need to know this information.