The term "complete protein" refers to amino acids, the building blocks of protein. There are 20 different amino acids that can form a protein, and nine that the body can't produce on its own.

These are called essential amino acids—we need to eat them because we can't make them ourselves. In order to be considered "complete," a protein must contain all nine of these essential amino acids.

Yes, meat and eggs are complete proteins, and beans and nuts aren't. But humans don't need every essential amino acid in every bite of food in every meal they eat; we only need a sufficient amount of each amino acid every day. Most dieticians believe that plant-based diets contain such a wide variety of amino acid profiles that vegans are virtually guaranteed to get all of their amino acids with very little effort.

Still, some people want complete proteins in all of their meals. No problem—meat's not the only contender. Eggs and dairy also fit the bill, which is an easy get for the vegetarians, but there are plenty of other ways to get complete proteins on your next meatless Monday. Here are some of the easiest:

QUINOA

Protein: 8 grams per 1 cup serving, cooked

A food so healthy that NASA hopes we'll grow it on interplanetary space flights, quinoa looks a lot like couscous, but it's way more nutritious. Full of fiber, iron, magnesium, and manganese, quinoa is a terrific substitute for rice and it's versatile enough to make muffins, fritters, cookies, and breakfast casseroles.

BUCKWHEAT

Protein: 6 grams per 1 cup serving, cooked

Buckwheat is, in fact, not a type of wheat at all, but a relative of rhubarb. The Japanese have turned the plant into funky noodles called soba. Buckwheat is crazy healthy: Some studies have shown that it may improve circulation, lower blood cholesterol, and control blood glucose levels.

HEMPSEED

Protein: 10 grams per 2 tablespoon serving

Relax, this hemp won't get anyone stoned. This relative of the popular narcotic contains significant amounts of all nine essential amino acids, as well as plenty of magnesium, zinc, iron, and calcium. They're also a rare vegan source of essential fatty acids, like omega-3s, which can help fight depression without the need to get high!

CHIA

Protein: 4 grams per 2 tablespoon serving

Chia seeds are the highest plant source of omega-3 fatty acids, and they contain more fiber than flax seeds or nuts. Chia is also a powerhouse of iron, calcium, zinc, and antioxidants, but the best thing about these little seeds is that they form a goopy gel when combined with milk or water. This makes them fantastic for making healthy puddings, thickening smoothies, or replacing eggs in vegan baking.

SOY

Protein: 10 grams per 1/2 cup serving (firm tofu); 15 grams per 1/2 cup serving (tempeh); 15 grams per 1/2 cup serving (natto)

While beans are normally low in the amino acid methionine, soy is a complete protein and thoroughly deserves its status as the go-to substitute for the meat-free (but go easy on the processed varieties). Tempeh and natto are made by fermenting the beans, but tofu is probably the best-known soy product. If protein's a concern, it's important to choose the firmest tofu available—the harder the tofu, the higher the protein content.

RICE AND BEANS

Protein: 7 grams per 1 cup serving

One of the simplest, cheapest, and vegan-est meals in existence is also one of the best sources of protein around. Most beans are low in methionine and high in lysine, while rice is low in lysine and high in methionine. Put 'em together, and what do you have? Protein content on par with that of meat. Subbing lentils or chickpeas for beans produces the same effect. These meals are a great way to load up on protein and carbohydrates after an intense workout.

SPIRULINA WITH GRAINS OR NUTS

Protein: 4 grams per 1 tablespoon

Contrary to popular belief, this member of the algae family is not a complete protein, since it's lacking in methionine and cysteine. All that's needed to remedy this is to add something with plenty of these amino acids, such as grains, oats, nuts, or seeds.

HUMMUS AND PITA

Protein: 7 grams per 1 whole-wheat pita and 2 tablespoons of hummus

The protein in wheat is similar to that of rice, in that it's only deficient in lysine. But chickpeas have plenty of lysine, giving us all the more reason to tuck into that Middle Eastern staple: hummus and pita. Chickpeas have a similar amino acid profile to most legumes, so don't be afraid to experiment with hummus made from cannellini, edamame, or other kinds of beans.

PEANUT BUTTER SANDWICH

Protein: 15 grams per 2-slice sandwich with 2 tablespoons of peanut butter

Every time legumes like beans, lentils, and peanuts are combined with grains like wheat, rice, and corn, a complete protein is born. Peanut butter on whole wheat is an easy snack that, while high in calories, provides a heaping dose of all the essential amino acids and plenty of healthy fats to boot. Experiment with nut butters like almond, cashew and more.