Answer :Jeanne P. Goldberg, PhD, director of the Center on Nutrition Communication and the Nutrition Communication Program at Tufts Friedman School, answers, This is really not difficult. In general, vegetables and grains are better sources of protein than fruits. Single groups of plant foods typically do not contain all of the essential amino acids in the balance that the body needs them, but if you eat a variety you will get all you need. For example, legumes are low in methionine, a sulfur-containing amino acid, but grains have quite a bit. On the other hand, grains are limited in lysine, which the legumes do have. By eating rice and beans together, the amino acid pattern of each is complemented. That approach, eating different vegetable foods together, serves to insure that people on vegetarian diets get all of the essential amino acids they need.