Plant Protein: A Vegan Nutrition Primer

a lentils and a bowlProtein is often a big worry for people contemplating a vegan diet. It’s important after all. We need it for muscles, bones, hormones, digestive enzymes, absorption of nutrients and to rebuild and replenish all kinds of cells. So knowing a little about sources of protein and recommendations for vegans can be helpful and reassuring.

Protein and Amino Acids

Proteins in foods and in the human body are composed of 20 amino acids. We humans can synthesize eleven of these as long as we get sufficient nitrogen from our diets. (Nitrogen is a component of every amino acid.)

The other nine amino acids—called essential amino acids (EAAS)—have to come from food since we can’t make them. So our need for protein is actually a need for these nine essential amino acids plus enough nitrogen to manufacture the other eleven.

Every plant protein contains all nine of the EAAs. They aren’t missing any of them, but (with the exception of soy protein) they are always a little low in one or two EAAs. As a result, the amino acid patterns in plants are a less precise match to human protein needs.

At one time, nutrition experts thought the answer to this was to combine proteins from different plant foods. Since grains and beans have complementary strengths and weaknesses in their EAA patterns, eating them together produced a “complete” amino acid pattern—that is, a pattern that mimics patterns found in human body proteins. And that wasn’t really a big deal, because historically, it’s the way most people have eaten: black beans and rice, lentil soup with bread, pinto beans with corn tortillas, hummus with pita bread.

Careful protein combining has turned out to be unnecessary, though. This is because the body maintains a reserve pool of amino acids from various sources for later use. Basically, your body can do its own “complementing” with the amino acids in a meal (1). The evidence also suggests that protein consumed at one meal can combine with protein consumed later in the day.

Protein combining is now considered an old-fashioned idea that isn’t relevant in vegan or vegetarian diets.

Getting Too Little Protein

While we never see vegans with overt protein deficiency (western vegans don’t get kwashiorkor), it doesn’t mean that all vegans consume optimal amounts. Marginal or suboptimal protein status can take a toll on health, affecting bone and muscle strength, for example (2,3).

Vegans who don’t eat enough calories or who don’t eat legumes run the risk of getting too little of this nutrient. And of course, those who eat a steady diet of junk are likely to fall short. (There isn’t much protein in vegan ice cream and potato chips.)

The Legume Connection

Legumes are important in vegan menus because they are the best plant sources of the EAA lysine. If you were getting all of your protein from grains, you could actually meet the RDA for total protein but still fall short of meeting lysine needs.

For example, a vegan woman could meet her total protein needs just by eating 10 cups of brown rice every day. But it would take about 14 cups of brown rice—about 2800 calories—to cover her needs for lysine.

In comparison, needs for both protein and lysine could be met by eating 4 cups of brown rice plus 2 cups of black beans, for a total of about 1200 calories. So yes, you can get enough protein and lysine without legumes, but it’s not very practical to do so.

Most vegans can meet lysine needs by eating two servings per day of legumes, but three servings provide a little more insurance. This is what a serving of legumes looks like:

½ cup cooked dried beans or lentils

½ cup tofu or tempeh

2-3 ounces soy-based veggie meat

1 cup soymilk (other plant milks are too low in protein

¼ cup peanuts

2 tbsp peanut butter


For people who struggle with legumes and can’t achieve those three servings for one reason or another, there are a few other foods that are rich in lysine. Quinoa and amaranth are two good choices. While they aren’t as rich in either protein or lysine as legumes, they are much better sources than other grains. You can replace a serving of legumes with one cup (not ½ cup—but a whole cup) of quinoa or amaranth.

You could also replace a serving of legumes with ¼ cup of pistachios or ½ cup of cashews. So it really is easy to eat three servings of legumes/lysine-rich foods even if you don’t love beans. Peanut butter on toast for breakfast, a hummus wrap for lunch, and a cup of quinoa for dinner would do it.

Vegan Protein Needs

Vegans may need a little extra protein because proteins in whole plant foods don’t seem to be as well-digested as those from animal foods. It’s a small difference, though. Based on the current RDAs, a 140 pound omnivore would need about 54 grams of protein while a vegan would require 60 grams.

An added complication is the fact that some protein experts believe that current recommendations are too low (4). Right now, protein recommendations from the World Health Organization are slightly (very slightly) higher than those of the U.S. (5).

This is an area where we don’t have all the answers. But you don’t need to calculate protein needs or track protein intake. If you follow the recommendations at the end of this article, you should have no problem meeting protein needs.

Protein Needs Throughout the Lifecycle

Newborn infants grow rapidly on diets that are only about 6% protein. It works well for them because they consume so much food and so many calories relative to their size.

We adults need diets that are considerably more protein dense since are calorie needs are lower relative to our protein needs. Vegans typically eat diets that provide around 10 to 14% of their calories as protein, or about 25 to 35 grams of protein per 1,000 calories (6). That’s sufficient for most people to meet protein needs at a reasonable calorie intake.

Many experts believe that protein needs are higher for older people (7,8). Since calorie needs sometimes also decline with aging, some older adults may need especially protein-dense diets. This is still a subject of debate, but sarcopenia—loss of muscle mass—is a serious public health problem for older people. A little extra protein may protect both muscle and bone health. Replacing some grains in diets with legumes, and eating more vegetables in place of fruits are ways to increase protein intake without increasing calories. You can find some examples of protein-packed meals for vegans here.

People on weight loss plans also need more protein dense diets. Eating a little more protein might also improve satiety and protect against muscle loss during weight loss.


How to Meet Protein Needs on a Vegan Diet

The rules for getting enough protein are simple:

  1. Get adequate calories
  2. Eat a variety of whole plant foods including at least 3 servings per day of legumes.
  3. If you are reducing your calorie intake or are over 60, add another serving or two of legumes to your menus to make your diet more protein dense. If you like them, consider including some soyfoods in menus since they are especially high in protein.


For more information about protein, please refer to chapter 2 in Vegan for Life.

And for a comprehensive overview of protein in vegan diets with all pertinent research, see the section on protein on the Vegan Health website.


  1. Young VR, Pellett PL. Plant proteins in relation to human protein and amino acid nutrition. Am J Clin Nutr 1994;59:1203S-1212S.
  2. Darling AL, Millward DJ, Torgerson DJ, Hewitt CE, Lanham-New SA. Dietary protein and bone health: a systematic review and meta-analysis. Am J Clin Nutr 2009.
  3. Lousuebsakul-Matthews V, Thorpe DL, Knutsen R, Beeson WL, Fraser GE, Knutsen SF. Legumes and meat analogues consumption are associated with hip fracture risk independently of meat intake among Caucasian men and women: the Adventist Health Study-2. Public Health Nutr 2013:1-11.
  4. Elango R, Humayun MA, Ball RO, Pencharz PB. Evidence that protein requirements have been significantly underestimated. Curr Opin Clin Nutr Metab Care 2010;13:52-7.
  5. World Health Organization. Protein and amino acid requirements in human nutrition. World Technical Series 935, Report of a Joint WHO/FAO/UNU Expert Consultation, United Nations University, 2007, Geneva.
  6. mangels R MV, Messina M. The Dietitian’s Guide to Vegetarian Diets. 3rd ed. Sudbury, MA: Jones and Bartlett, 2010.
  7. Gaffney-Stomberg E, Insogna KL, Rodriguez NR, Kerstetter JE. Increasing dietary protein requirements in elderly people for optimal muscle and bone health. J Am Geriatr Soc 2009;57:1073-9.
  8. Paddon-Jones D, Rasmussen BB. Dietary protein recommendations and the prevention of sarcopenia. Curr Opin Clin Nutr Metab Care 2009;12:86-90.


© Virginia Messina, MPH, RD


Print Friendly