I found a dietician named Dina Aronson on the Veg Family website. Here was her response to a question posed about vegans and protein/amino acid needs:
“As you indicated, protein is made up of smaller building blocks called amino acids. The foods we eat contain differing amounts of these amino acids, and our bodies use them to make the protein that we need for cell and tissue structure and function.
There are about 20 amino acids that humans need to make protein. Eight of these amino acids are essential, meaning that we must obtain these amino acids from foods (vegetarian or not). The remaining amino acids are both in foods and can be made by the body as needed.
You need to look no further than a biology textbook to discover that all the amino acids humans need for optimal health are found in plant foods. When you think about it, this makes sense, because where does the cow and chicken get these amino acids (that end up in the meat humans eat)? From plants, of course! With the exception of soybeans, there is no ONE plant food that supplies all of the essential amino acids, but a variety of plant foods will most definitely meet our protein needs. Protein deficiency is simply not an issue among well-nourished vegans who consume a variety of foods from the four main food groups (grains, legumes, vegetables, and fruits).
It was once believed that vegetarians had to consume “complementary” proteins at the same meal in order for our body to process them correctly. For example, grains are a good protein source but are low in the amino acid lysine, while beans have plenty of lysine. So it was once thought that eating rice with beans supplied “complete” protein. However, nutrition experts have found that protein complementation is not necessary; the body stores “pools” of amino acids in our body so that they’re ready to be used when needed. As long as these different sources of protein are eaten over the course of the day, we’re covered.
If it were true that vegans had a hard time getting enough amino acids, we would all have symptoms of protein deficiency. It turns out that protein deficiency is very rare, but certainly there are ways that a vegan can actually get too little protein:
1. By eating mostly junk food and little else (e.g. potato chips, refined white flour products, candy, etc.), because refined junk foods are low in protein, and excessive junk food can displace healthy, protein-rich plant foods in the diet.
2. By not getting enough calories (long-term illness, anorexia nervosa, etc.), which results in deficiency of not just protein, but most nutrients.
Bottom line: Eat enough and a good variety of whole plant foods, and your amino acid/protein needs will automatically be met.”
(The link to this is http://www.vegfamily.com/dietician/0105a.htm)