The human body has no mechanism for storing protein, so if you don’t eat enough protein in each meal then you’re depriving yourself if the body’s building blocks: amino acids (the units of all proteins). Some amino acids can be made by the body from others. Those that cannot be made from others are called essential amino acids, because without them, the body is not able to do some things that it can do with all essential amino acids. Quinoa is one of a few vegetable sources of all essential amino acids (meat also supplies all essential amino acids).
This protein calculator is a handy too for determining how much protein you should way in a day (RDA: Recommended Daily Allowance).