Proteins provide the framework for every cell of the body. Tissues that are growing and those undergoing repair need a steady supply of protein to build and rebuild organs, muscles, antibodies, hormones and enzymes. Everybody needs protein.
For most Americans, getting enough protein is not a problem. Also, unlike fats and carbs, there is no such food as an unhealthy protein.
A complete protein contains all nine of the essential amino acids.
An incomplete protein is missing one or more of the nine.
Animal and Plant Source Proteins
Foods that come from animal sources contain complete proteins. Both grains and legumes contain significant amounts of protein but these proteins are incomplete proteins. A variety of plant proteins combined will complement each other in amino acid make up. Eating a varied diet of plant foods will give you a total of all nine essential amino acids.
Plant proteins that complement each other are familiar combinations.
whole wheat bread + peanut butter
brown rice + beans
corn tortillas + beans
whole wheat pita bread + hummus
And with dairy products,
cereal + milk
pizza + cheese
granola + yogurt
broccoli + cheese
To get the benefit of combining complementary protein sources you do not have to consume them at the same meal, just some time during the same day. Your body will do the thinking for you as to how to combine the proteins you consume each day.
Note: Getting too much protein is usually not a problem. You would have to eat an awful lot of protein over a long period of time. Note that a currently popular "weight loss" diet suggests that you eat a high protein diet while eliminating carbohydrates. This diet overworks your kidneys as they try to get rid of the excess protein and you lose a lot of water in the process. Much of the weight loss this diet results in is water loss. High protein weight loss diets are gimmicks that have the potential of causing harm. The best diet for regulating body composition is a varied and balanced diet containing the full spectrum of nutrients a body needs in the amounts appropriate for each individual body.