Earlier quoted context omitted.
Most plant-derrived protein sources have an incomplete profile of amino acids. Humans have eight essential amino acids (amino acids that we must get from the diet as we cannot synthesize them) that are plentiful in animal sources and lacking to various degrees in plant sources. Plant sources of protein, even when combined to provide all the essential amino acids, are too heavy in carbohydrate, irritate the gut, and s…
So you combine beans and grains. That is how most of humanity exists, after all. I think the last part of your comment is patently untrue. The American Dietetic Association released a position paper stating that they believe vegetarian and vegan diets are perfectly healthy and sustainable. http://www.ncbi.nlm.nih.gov/pubmed/12826028
This research has been around for 11 years and to my knowledge has gone unchallenged and mostly ignored:
http://www.ncbi.nlm.nih.gov/pubmed/10489816
Just like the research showing that diabetic complications could be averted via normalizing blood sugars in the 1970’s or that gluten could actually be an allergen and that celiac disease is a real condition in the 1990’s.
As a vegetarian or vegan you can definitely survive, but you won't thrive.