A food can be called a complete protein when it has sufficient amounts of the nine essential amino acids.

Animal proteins are complete protein sources. But vegetarians who get their protein from fruits, vegetables, nuts, grains and legumes -- many of which are incomplete proteins -- should be mindful to redress the balance.

A simple way to do this is to eat some beans with your rice, which together create the equivalent of a complete protein. This practice of "protein combining" is an easy way to make sure you're getting enough protein, although the notion that rice and beans have to be eaten in the same meal has been widely debunked.

You can also incorporate non-animal complete protein sources such as soy, quinoa, buckwheat and spirulina into your diet.