You can meet your need for protein with a wide variety of foods; from animal sources alone, from both plant and animal sources, or from specific plant-protein combinations. This variety is possible because the body’s need for protein is not a need for a particular food – or a particular nutrient – but is a combined need for various amounts of 22 different amino acids. The combinations in which protein foods are eaten are just as important as the foods themselves.
While high-quality protein foods such as milk, eggs, meat, poultry, and fish will supply all the amino acids you need for protein synthesis in a single food, these are not the only contributors of dietary protein. Grains such as wheat, rice, and corn, potatoes, and leafy vegetables provide lesser quality protein that is an important source of all amino acids as well as vitamins, minerals, and fiber.
By supplementing a vegetable-source protein food with animal-source protein food, you obtain a total amount of dietary protein equal to the dietary protein from a large amount of animal protein alone. Some studies have suggested that combinations of foods from different sources are more beneficial than single protein foods.
Apparently, the more different amino acids you eat, the better off you are.
You can also obtain high-quality, or complete, protein without any animal foods – by pairing two specific incomplete proteins in a meal, such as the corn and beans mentioned earlier – a method used by many vegetarians. Although this diet can be a healthful one, vegetarians must carefully choose from a wide variety of foods to meet their full need for high-quality protein. In addition, they must bear in mind that relatively large quantities of plant foods have to be eaten to match the amount of protein one would get from animal sources.