From Dr. Fuhrman's book Eat to Live:
Remember those four basic food group charts we all saw in every classroom in elementary school? Protein had its own box, designated by a thick steak, a whole fish, and an entire chicken. Dairy foods had their own special box as well. A healthy diet, we were taught, supposedly centered on meat and milk. Protein was thought to be the most favorable of all nutrients, and lots of protein was thought to be the key to strength, health, and vigor. Unfortunately, cancer rates soared. As a result of scientific investigations into the causes of disease, we have had to rethink what we were taught. Old habits die hard; most Americans still cling to what they were taught as children. There are very few subjects that are more distorted in modern culture than that of protein.
Keep in mind that we do need protein. We can't be healthy without protein in our diet. On the other hand, plant foods have plenty of protein, and you do not have to be a nutritional scientist or dietician to figure out what to eat and you don't need to mix and match foods to achieve protein completeness. Any combination of natural foods will supply you with adequate protein, including all eight essential amino acids as well as unessential amino acids.
It is unnecessary to combine foods to achieve protein completeness at each meal. The body stores and release amino acids needed over a twenty-four-hour period. About one-sixth of our daily protein utilization comes from recycling our own body tissue. This recycling, variation from meal to meal in amino acid "incompleteness." It requires no level of nutritional sophistication to get sufficient protein, even if you eat only plant foods.
It is only when a vegetarian diet revolves around white bread and other processed foods that the protein content falls to low levels. However, the minute you include unprocessed foods such as vegetables, whole grains, beans, or nuts, the diet becomes protein-rich.
Still need more convincing? Check out this post from last month: Popeye Was Right--Greens Pack a Powerful Punch