Proteins: Complete and Incomplete
There are differences in the types of proteins you eat, some are "complete;" others are "incomplete," and you need them both. Proteins are made of 20 or so building blocks called amino acids. Complete proteins contain the 9 essential amino acids your body needs to build new proteins. Essential amino acids are ones the body can't produce on its own. Animal sources of protein tend to be complete. Other protein sources lack one or more of the essential amino acids; these are called incomplete proteins. These include fruits, vegetables, grains and nuts.
Because the body doesn't store amino acids, like it does with fat or carbohydrates, it needs a fresh supply of them every day to make new proteins. Complete and incomplete proteins play an equally important role in this process. The best way to get all the protein you need is to pick from wide and varied sources.