Combining Proteins on a Vegetarian or Vegan Diet

If you're following a vegetarian or vegan diet, focusing on complementary proteins is said to maximize nutrition and improve health. Including complementary proteins in your diet involves combining certain protein sources in order to achieve adequate intake of compounds called amino acids.

Amino acids are considered the building blocks of protein. Although some amino acids can be synthesized in your body, others (called "essential amino acids") must be ingested from food.

There are nine types of essential amino acids, including: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

These essential amino acids can be found in both animal sources and plant sources of protein. Animal sources of protein (such as meat, poultry, fish, dairy, and eggs) are considered complete proteins since they contain sufficient levels of all nine essential amino acids.

On the other hand, plant sources of protein (such as beans, legumes, nuts, seeds, and soy) tend to be high in certain essential amino acids but lacking in others. For example, grains are low in the amino acid lysine, while legumes are rich in lysine.

Why Do People Include Complementary Proteins in Their Diets?

For the vegetarians and vegans whose diets lack animal sources of protein, including complementary proteins in meals and snacks is said to protect against any deficiencies in amino acid intake.

It's thought that combining two or more plant sources of protein can allow vegetarians and vegans to obtain sufficient levels of all the essential amino acids.

One of the most important components of your diet, protein is needed to keep your muscles, bones, skin, hormones, and immune system functioning properly.

Protein also makes up the enzymes that play a key role in many crucial biological processes, such as digestion.

The recommended daily allowance (RDA) of protein is 0.8 g per kg of body weight. For example, a 130-pound sedentary adult needs 47 g of protein per day. Since this requirement increases with physical activity, adults who exercise regularly typically need about 70 g of protein daily.

Examples of Complementary Proteins

There are many different ways to include complementary proteins in a vegetarian or vegan diet. Here are some examples of food pairings that provide complementary proteins:

soups or stews that include legumes and grains
salads made with beans and nuts or seeds
a peanut butter sandwich on whole-grain bread
hummus with whole-wheat pita bread
tofu or tempeh with brown rice or quinoa
tofu stir-fry with whole-grain noodles and peanuts
beans and brown rice
yogurt with sunflower seeds or almonds

Should You Use Complementary Proteins?

It was once commonly believed that vegetarians and vegans needed to consume complementary proteins at each meal in order to stay healthy. However, it's now known that simply eating a wide variety of plant foods every day can allow you to get all the protein you need.

According to the National Institutes of Health, top plant sources of protein include:

almonds
black beans
garbanzo beans
hazelnuts
kidney beans
lentils
peanut butter
peanuts
pinto beans
split peas
sunflower seeds
tempeh
tofu
walnuts

Some research suggests that getting your fill of plant sources of protein may help stave off certain diseases. This research includes a 20-year study of 82,802 women, published in the New England Journal of Medicine in 2006.

In this study, researchers determined that women who followed low-carbohydrate diets high in plant sources of protein (as well as plant sources of fat) had a 30 percent lower risk of heart disease (in comparison to those who followed high-carbohydrate, low-fat diets).

The study also found that participants who stuck to diets high in animal sources of protein and fat did not have a reduced risk of heart disease.

In addition, there's some evidence that choosing plant sources of protein can help with weight control. In a research review published in the journal Obesity in 2014, for instance, scientists analyzed nine previously published clinical trials and found that daily intake of beans, chickpeas, lentils, or peas may help with weight maintenance by increasing feelings of fullness.

Go here to learn about different types of alternative diets, including some vegetarian diets.

Sources:

Halton TL, Willett WC, Liu S, Manson JE, Albert CM, Rexrode K, Hu FB. "Low-Carbohydrate-Diet Score and the Risk of Coronary Heart Disease in Women." N Engl J Med. 2006 Nov 9;355(19):1991-2002.

Li SS, Kendall CW, de Souza RJ, Jayalath VH, Cozma AI, Ha V, Mirrahimi A, Chiavaroli L, Augustin LS, Blanco Mejia S, Leiter LA, Beyene J, Jenkins DJ, Sievenpiper JL. "Dietary Pulses, Satiety and Food Intake: a Systematic Review and Meta-Analysis of Acute Feeding Trials." Obesity (Silver Spring). 2014 Aug;22(8):1773-80.

National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. "Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids." National Academy Press. Washington, DC, 2005.

U.S. Department of Health and Human Services and U.S. Department of Agriculture. "2015-2020 Dietary Guidelines for Americans. 8th Edition." December 2015.