Protein is in everything you eat and protein is protein but they are not all equivalent. Getting a complete protein by combining foods is an outdated concept. You do not need to worry about combining rice and beans etc. but you do need to worry about utilization protein. Dr. Fuhrman does make allowance for 3 oz of animal protein a day.

You can get plenty of protein by eating a vegan diet. The only difference I have found is in the utilization of plant protein vs animal protein and also they chemical composition is a bit different.


Protein is not necessarily the same in all form. One area to be careful is in getting sulfur containing amino acids. You can get the sulfur containing amino acides by eating certain plants such as cauliflower and broccoli, but our bodies do not utilize the sulfur containing amino acids from plants as readily as the animal sources of sulfur containing amino acids (eggs, etc). New studies are showing that these proteins are important of metabolism.



http://jn.nutrition.org/content/136/6/1636S.full
The sulfur-containing amino acids: an overview.
Brosnan JT1, Brosnan ME.
Author information
Abstract

Methionine, cysteine, homocysteine, and taurine are the 4 common sulfur-containing amino acids, but only the first 2 are incorporated into proteins. Sulfur belongs to the same group in the periodic table as oxygen but is much less electronegative. This difference accounts for some of the distinctive properties of the sulfur-containing amino acids. Methionine is the initiating amino acid in the synthesis of virtually all eukaryotic proteins; N-formylmethionine serves the same function in prokaryotes. Within proteins, many of the methionine residues are buried in the hydrophobic core, but some, which are exposed, are susceptible to oxidative damage. Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways. Methionine metabolism begins with its activation to S-adenosylmethionine. This is a cofactor of extraordinary versatility, playing roles in methyl group transfer, 5'-deoxyadenosyl group transfer, polyamine synthesis, ethylene synthesis in plants, and many others. In animals, the great bulk of S-adenosylmethionine is used in methylation reactions. S-Adenosylhomocysteine, which is a product of these methyltransferases, gives rise to homocysteine. Homocysteine may be remethylated to methionine or converted to cysteine by the transsulfuration pathway. Methionine may also be metabolized by a transamination pathway. This pathway, which is significant only at high methionine concentrations, produces a number of toxic endproducts. Cysteine may be converted to such important products as glutathione and taurine. Taurine is present in many tissues at higher concentrations than any of the other amino acids.