Protein is a macronutrient that is essential to your diet. Proteins exist in all your cells, providing structure in the form of muscles, skin and organs. Proteins also function in growth, cell and tissue formation and repair, synthesis of enzymes and hormones and maintaining your immune system. If your diet lacks sufficient carbohydrates or fats, your body may burn protein as fuel. The amount of protein you need every day depends on your size, physical condition and state of health, and the quality of the protein in your foods determines the optimal way for you to structure your diet.
Background
Amino acids are small molecules that, when linked together in a specific configuration, create a protein. The function of the protein depends not only on how they join together but also on the particular amino acids making up the protein. When you consume protein, your digestive system breaks the protein down into its constituent amino acids, and this pool of amino acids is then used to synthesize new proteins as your body needs them. Nutritionists classify nine specific amino acids as essential; that is, your diet must contain them because your body cannot manufacture them.
Complete vs. Incomplete Proteins
Complete proteins contain all nine essential amino acids. Nutritionists refer to complete proteins as high-quality proteins, because they supply all the amino acids your body is unable to synthesize. Animal sources of protein, such as meat, fish, dairy products and eggs, provide all nine essential amino acids and are therefore high-quality proteins. A few plant sources of protein, such as soy products, are also complete, but most are incomplete, states the Utah Education Network. Incomplete proteins lack one or more of the nine essential amino acids that your body needs.
Protein Combinations
If the proteins you consume are incomplete, you may still supply your body with all nine essential amino acids by combining incomplete proteins together in your diet. The protein-building machinery of your body does not care where its amino acids originate as long as the pool of amino acids contains all the building blocks it needs. Combining incomplete proteins for optimal nutrition requires understanding which foods lack which amino acids so that you combine them in a way to provide all necessary amino acids. Examples of these so-called complementary proteins include rice and beans, corn and beans, peas and pasta or peanut butter and wheat bread.
Other Considerations
According to the Centers for Disease Control and Prevention, you do not need to consume complementary proteins together or with the same meal, as long as they are eaten at some point throughout the day. If your protein sources are consistently incomplete, consult with your health-care provider to be sure your diet contains sufficient nutrients that may be lacking in plant-based foods, such as calcium, iron, zinc, vitamin D and vitamin B12.
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