Ask the RD
Answer: The importance of protein in our diet cannot be understated, especially when we are engaged in an exercise regimen. Luckily, we can obtain protein from a variety of animal and plant sources.
Unfortunately, all proteins are not created equal. Proteins are made up of a variety of amino acids, which link up to form the proteins. There are 21 amino acids that can be mixed and matched to form proteins. The human body can make 11 amino acids on its own, but we must obtain the other nine from our diet. The nine we must ingest are called essential amino acids. A food that contains all nine essential amino acids is called a complete protein and is considered a high-value food. Animal proteins are complete proteins, as are a few plant foods, such as soy products and quinoa.
If you are vegan and therefore choose to avoid all animal products, it is important to eat a variety of foods that will supply your protein needs. All plant foods (except fruit) contain proteins and a variety of amino acids, but these are generally not complete proteins—they may be low in one or more essential amino acids. The essential amino acid missing from the plant food is referred to as the limiting amino acid. The trick is to combine your foods so that you create a complete protein. For example, lysine is the limiting amino acid in grains, while methionine and tryptophan are limiting in legumes. When a grain and a legume are eaten together (e.g. rice and beans), the limiting amino acids are offset, and a complete protein is created.
If you feel you want to supplement your protein intake with a protein shake, keep in mind that many protein powders are not vegan. Many are made with whey, which is a dairy derivative. Vegan protein powders do exist, but you need to search them out.