Complete proteins are foods that contain all of the nine essential amino acids that make up protein. There are at least 20 amino acids, but the nine considered essential for daily human consumption are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Complete protein foods, or a sufficient combination of incomplete proteins, must be consumed daily. The body needs to take in the essential amino acids for healthy functioning each day, but cannot produce them naturally.
Meat, fish, and poultry are complete animal proteins. Cheese, eggs, and milk are also animal products that are complete proteins. Examples of plant-based complete protein sources are soybeans, buckwheat, and quinoa. The body absorbs animal-based proteins much easier than plant sources, so vegetarians must be especially careful to consume enough complete protein sources. The essential amino acids lysine and tryptophan are found mostly in animal proteins; however, soybeans are a vegetable protein choice that contains all of the essential amino acids.
While a complete protein has all nine amino acids, an incomplete source either has insufficient amounts of them or is missing one or more. Eating nutritiously by combining incomplete proteins need not be difficult. Incomplete proteins don't even have to be consumed at the same meal, as long as they're eaten each day. The body will still digest them together on a short term basis.
There are many different possible mixtures of incomplete proteins that form a complete protein source. For example, the wheat in whole wheat bread combined with peanut butter creates a complete protein. A peanut butter sandwich with a glass of milk and an apple is often considered a healthy lunch, as it offers a complete protein source as well as a fruit and a dairy choice. Other popular complete protein blends include rice with beans, and oats with nuts such as in granola. A vegetarian dish could include lentils and corn, as these create a complete plant-based protein.
Getting enough complete proteins throughout the day isn't difficult as long as a balanced, nutritious diet is consumed. It's important to note that an excess of protein isn't needed and may do more harm than good. Eating the recommended amount of protein along with other essential foods each day in a balanced diet should be the focus. Athletes and pregnant or nursing women do often require more complete proteins than other people, but these amounts should still be in balance with the rest of the diet.