Protein provides important amino acids. Of the 20 amino acids we get from plant and animal proteins, there are nine that are considered essential, meaning that the body can’t synthesize them on its own so we need to get them from food—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Protein recommendations are based on roughly how much we need to eat to cover our needs for these various amino acids. Most healthy adults need about 0.8 to 1.0 gram of protein per kilogram of body weight. Since 1 kilogram is equivalent to 2.2 pounds, a 150-pound person (68.2 kilograms) needs about 55 to 68 grams of protein per day.
Just note that someone on a vegetarian diet likely needs more than someone who eats animal products in order to get all those essential amino acids. Some proteins, like animal proteins, for example, are called “complete proteins” because they provide all the essential amino acids. With a few exceptions, most plant proteins provide only some, which is why they’re sometimes called “incomplete proteins.”
Plant proteins that are complete include soy, quinoa, buckwheat, and Quorn. Combining complementary plant proteins can also help you cover your bases. A few classic combos are rice and beans, whole wheat or sprouted grain bread with nut or seed butter, and pasta with peas.