Protein from beans, grains, nuts and seeds

By Vesanto Melina, RD,

Absorbing more protein from plant foods is the final topic in this blog post. To discover that information, be sure to read all the way to the bottom, past the first set of endnotes.


What’s the story with complete and incomplete proteins?

In the early 1970’s Frances Moore Lappé wrote about a need to combine “incomplete proteins” in the same meal. Many people got the impression that it was helpful to classify foods as either “complete proteins” (better) or “incomplete proteins” (worse).

Ten years later, Ms. Lappé retracted her statement. Since the 1970’s, our understanding of human protein needs has come a long way.

Some misconceptions about protein arose due to studies on animals. As it turns out, baby rats — who double their weight in four days and grow fur all over their bodies — have very different amino acid requirements from humans, who have no desire to do either.

For example, baby rats do OK on cow’s milk, but will die on a diet of human milk. In animal studies, rats were given a single plant protein source — such as wheat protein — plus enough vitamins, minerals, and calories. The rats didn’t do well at all on a single source of protein.

Rats require as much as 50% more of certain amino acids than humans do. Our early reliance on such studies has led many people, including scientists, to undervalue plant protein quality.[1-4]

But unless you were living in severe poverty with limited food choices, you would not live on a single food (such as wheat or rice) as your protein source. Humans require a variety of foods for optimal health.

Essential Amino Acids


Adults require eight essential amino acids in specific amounts. They’re called “essential” because you must get them from food. (Infants require nine essential amino acids, with histidine as the additional amino acid.)

In the tables below, the phrase “amino acid scoring pattern” describes the amount of each essential amino acid humans need – per gram of protein.

For example, according to the 2007 report of the Food and Agriculture Organization and the World Health Organization, adults require 45 mg per gram of protein and 6 mg of tryptophan per gram of protein.

In early studies, foods were deemed “incomplete proteins” when their amino acid patterns did not match the amino acid pattern required by humans.

However, with the exception of gelatin (an animal product), plant and animal proteins provide every one of the essential amino acids.

Table 1: Amino acid scoring patterns from the 1973 and 1985 FAO/WHO/UNU reports. On the left is the list of amino acids, on the right is a score representing the mg per gram of protein.[3a]

Amino Acids 1973 Report[1a] 1985 Report[2a]
(2–5 y)b
(10–12 y)
(under 75)
Histidine 40 19 19 16
Isoleucine 28 28 13
Leucine 70 66 44 19
Lysine 55 58 44 19
SAA 35 25 22 17
TAA 60 63 22 19
Threonine 40 34 28 9
Tryptophan 10 11 (9) 5
Valine 50 35 25 13
Total 360 339 241 127

To be used for young and older children and adults recognizing it might underestimate the quality for adults.


Calculated with safe protein intakes, (g/kg/d). i.e. children (2—5 years), 1—10, children (10—12 years), 0—99 adults, 0—75.


Requirement as mg/kg/d divided by the safe or average protein requirement as indicated.

Table 2: Amino acid scoring patterns from the 2007 FAO/WHO/UNU reports. On the left is the list of amino acids, on the right is a score representing the mg per gram of protein.[5a]

Amino Acids 2007 Report[4a]
  Infants Preschool
(1–2 y)
(3–10 y)
(under 66)
Histidine 20 18 16 15
Isoleucine 32 31 30 30
Leucine 66 63 61 59
Lysine 57 52 48 45
SAA 27 25 23 22
TAA 52 46 41 38
Threonine 31 27 25 23
Tryptophan 8 7 7 6
Valine 43 41 40 39
Total 336 310 291 277

Calculated with average protein requirement values (g/kg/d). i.e. infacts 1 to 12 months, preschool children 1 to 2 years, children and adolescents 3 to 10, adults up to age 66.


Requirement as mg/kg/d divided by the safe or average protein requirement as indicated.

Diets of just one thing (“mono diets”) are a bad idea, even for a food that has a high rating in terms of amino acid pattern. Your dietary needs are too complex to be met by any one food. However, if you ate enough of any one protein source, plant or animal, you’d get every amino acid you needed.

What is the “ideal” reference pattern for human requirements?

The answer to this question is the subject of controversial debate among nutritional scientists. The answer varies at different stages of life — infancy, adulthood — as shown in the table below.[1-7]

This chart gives amounts (in milligrams) of each of the 9 amino acid acids per gram of protein. All plant foods contain every one of these essential amino acids.

Why are there no lists of amino acid scores in current scientific literature?

The ideal “human scoring pattern” is still the subject of much debate, making it difficult to choose a reference. (Examples of scoring patterns that have been used are shown in the table above.)

Today, the standard method for evaluating protein quality is the “protein digestibility corrected amino acid score” or “PDCAAS”. However, this method is controversial and evolving.

The PDCAAS depends on two factors: digestibility and amino acid content. Gram for gram, it compares the amino acids in a food (corrected for digestibility) with human protein requirements.

Before furthering this point, we want to make clear that we don’t recommend eating beef, and we recognize that vegans don’t eat eggs. However, the best way to understand the common concerns about plant proteins is to compare them with animal proteins.

The PDCAAS scores for egg and cow’s milk is 100, for beef is 92, and for soy is 91, and for wheat is 42.[1-7]

Note that these are estimates; human digestibility is estimated rather than measured exactly. So you may see slightly different numbers depending (for example) on how these foods are prepared.

Beef, egg, and soy have patterns close to estimated requirements from the 1985 report of preschool children suffering from malnutrition (shown in the table above) and of the 2007 adult requirements.

Does this mean we should eat eggs or beef daily?

Getting all — or even most — of your protein from beef or egg would put your cholesterol intake through the roof. Also, it would put you at risk for a great many chronic diseases including cardiovascular disease and several types of cancer.

As a further example, since soy foods are highly nutritious, two men chose to center their diets on massive amounts of soy. The first man had twelve servings of soy per day. The second consumed twenty, which was the majority of his calories. This led to serious health problems.

That sort of dietary imbalance deprives you of essential nutrients and phytochemicals that would otherwise come from other highly nutritious, protein-rich foods.

It is no longer certain how closely amino acid patterns in food match the requirements of healthy children (who are unavailable for research purposes), or even of adults (because it is a matter of some debate).

The patterns of soy protein isolate and egg white meet an adult amino acid pattern so closely they are given a score of 100%. Soy and beef are a match of approximately 91-95%. In other words, if you eat about 5-10% more of the particular lacking amino acid, you meet your protein requirements.

In practical terms, this means raising your recommended protein intake to 0.9 grams of protein per kg body weight, as suggested in Lesson 14.1.

Other foods have lower scores. Researchers see different scores for various plant foods depending on the rodent or estimated human amino acid pattern that was used as a reference. However, by using a mix of plant foods, they can easily match the overall amino acid pattern to requirements.[1-7]

For vegetarians, eggs and dairy products are good sources of protein, in terms of their amino acid contribution.

Now we know that every plant food contains every one of the essential amino acids. But when one or two are in short supply, can you meet your amino acid requirements by eating more of that same food?

From a health perspective it does not make sense for you to eat a single food, such as soy or egg, to meet your protein needs. Using any one food as your sole protein source would bring you health risks and would be unwise. You need a mix of foods for optimal nutrition. Each food you eat will provide a slightly different pattern of amino acids.[9-11]

Food exceptions include human breast milk and infant formula. Nature and formula companies have specially fashioned these to meet infant requirements.

Do complimentary foods need to be eaten in the same meal?

Suppose you eat whole wheat toast for breakfast, brown rice with vegetables for lunch, and black bean soup for dinner.

Both whole wheat toast and brown rice are low in lysine but relatively high in methionine. Black beans are low in methionine but relatively high in lysine.

In other words, while each meal would have all of the essential amino acids, each meal would beslightly short in one amino acid. That’s relative to the estimated reference pattern in Table 1, above.

Does it matter how far apart, or how close together, these meals are eaten?

No, because your body can pool and retain amino acids over the course of a 24 hour period. Thus, your body can draw on all the amino acids it needs from the “pool” for its protein building and maintenance requirements.

You should note that every vegetable will contribute its unique pattern of amino acids, further adding to the mix.[12-14]

It doesn’t matter which foods you eat at breakfast, lunch, or dinner. Humans worldwide do well on a variety of different meal patterns.

The protein you derive from various food groups is shown in the table below.

The minimum servings listed in Column 1 will meet the recommended protein intake for someone weighing 120 lbs (including a safety margin). But you can easily eat more than the minimum servings.

Legumes (beans, lentils, soy products, and peanuts) are significant protein providers. So are nuts and seeds. So it’s wise to include them at each meal, or at two meals and one snack.

For example, spread 4 Tbsp nut butter on two slices of whole grain bread, and you’ll get four servings of protein (2 servings from the nut butter and 2 servings from the bread). Between meals, you can snack on a handful of nuts or raw peas in the pod.[15-17]

You can also whip up a salad dressing containing ½ cup silken tofu or ¼ cup tahini, consume it with lunch and dinner, and you’ll get another serving of protein.

Note: Tofu and tempeh can be twice as high in protein as shown in the chart below, per half cup. Check labels.

Protein From Each Food Group

Food group
(minimum servings per day)
Examples of a single serving Approximate protein contribution per serving, grams Total protein from minimum servings, grams
(3 or more servings)
½ cup cooked beans, peas, lentils, tofu, or tempeh
1 cup raw peas or sprouted lentils or peas
¼ cup peanuts
2 Tbsp peanut butter
1 cup soy milk
1 ounce vegetarian meat alternative
9.6 g 28.8g
(3 or more servings)
½ cup cooked cereal, rice, pasta, quinoa, or other grain or grain product
1 ounce (1 slice) bread
½ cup raw corn or sprouted quinoa, buckwheat, or other grain
1 ounce ready-to-eat cereal
3.3 g 9.9 g
(5 or more servings)
½ cup raw or cooked vegetables
1 cup raw leafy vegetables
½ cup vegetable juice
1.3 g 6.5 g
Nuts and seeds
(1 or more servings)
¼ cup nuts and seeds
2 Tbsp nut or seed butter
5.5 g 5.5 g
(4 or more servings)
1 medium fruit
½ cup fruit or fruit juice
¼ cup dried fruit
0.85 g 3.4 g


  1. [1] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  2. [2] Millward DJ et al. Protein quality assessment: impact of expanding understanding of protein and amino acid needs for optimal health. Am J Clin Nutr. 2008;87(5):1576S-1581S.
  3. [3] Schaafsma G. The protein digestibility-corrected amino acid score. J Nutr. 2000;130(7):1865S-7S.
  4. [4] Schaafsma G. The Protein Digestibility-Corrected Amino Acid Score (PDCAAS)–a concept for describing protein quality in foods and food ingredients: a critical review. J AOAC Int. 2005;88(3):988-94.
  5. [5] Craig WJ et al. Position of the American Dietetic Association: Vegetarian Diets. J Am Diet Assoc. 2009;109 (7)1266-82.
  6. [6] Reeds PJ. Dispensable and indispensable amino acids for humans. J Nutr. 2000;130(7):1835S-40S.
  7. [7] Ruales J. Nutritional quality of the protein in quinoa (Chenopodium quinoa, Willd) seeds. Plant Foods Hum Nutr. 1992 Jan;42(1):1-11.
  8. [8] Millward DJ et al. Amino acid scoring patterns for protein quality assessment. Brit J. Nutr. 2012;(108)S31-S43.
  9. [9] Craig WJ et al. Position of the American Dietetic Association: Vegetarian Diets. J Am Diet Assoc. 2009;109 (7)1266-82.
  10. [10] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  11. [11] Mangels AR, Messina V, Messina M. The Dietitians Guide to Vegetarian Diets. Jones and Bartlett Learning Ltd. 2011.
  12. [12] Craig WJ et al. Position of the American Dietetic Association: Vegetarian Diets. J Am Diet Assoc. 2009;109 (7)1266-82.
  13. [13] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  14. [14] Mangels AR, Messina V, Messina M. The Dietitians Guide to Vegetarian Diets. Jones and Bartlett Learning Ltd. 2011.
  15. [15] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  16. [16] Davis B et al. Becoming Vegan: Express Edition. The Book Publishing Co. 2013.
  17. [17] Mangels AR, Messina V, Messina M. The Dietitians Guide to Vegetarian Diets. Jones and Bartlett Learning Ltd. 2011.


Vegans are often slim; is this due to less muscle mass or protein intake?

Vegans typically have less body fat (and are slimmer) than lacto-ovo vegetarians and omnivores. Is this good news or bad news?

Let’s begin with two large studies which found that the average vegan’s body size is healthier, rather than underweight… the EPIC-Oxford study in the UK and the Adventist Health Study-2.

These studies compared the BMI (Body Mass Index) of vegans with other dietary groups, including health-conscious meat eaters, fish eaters, and lacto-ovo vegetarians. “Meat eaters” were defined as those who consumed meat more than once per week.[1-3]

The Body Mass Index is a weight-to-height ratio; anything from 18.5 to 24.9 is considered healthy. Anything below that is considered “underweight”.

In the first study – the EPIC-Oxford study – vegans had the lowest Body Mass Index, ranging from 21.98 to 23.6.

Health-conscious meat eaters had a Body Mass Index at the top end of the healthy range. Of course, the British population tends to be slimmer than North Americans.

In the second study – the Adventist Health Study-2 – vegans were the only dietary group whose average Body Mass Index was in the healthy range.

Despite these studies, there may be a higher proportion of vegans who are underweight, compared to the general population. However, data is currently very limited.

A small American study reported that 36% of its vegan participants (9 out of 25) had a Body Mass Index of less than 19. In this report, a larger proportion of vegans fell near or below the BMI cutoff for underweight (vs. the general population).

The Oxford Vegetarian Study analyzed approximately 11,000 vegetarians and vegans. More than 20% had a Body Mass Index of 18 to 20. (Again, the healthy range is considered to be 18.5 to 24.9.)

In fact, more of these participants had a Body Mass Index under 18 (underweight) than a Body Mass Index over 28 (overweight).[2]

The Giessen (raw food) study in Germany reported high rates for raw vegans being underweight. 25% of raw vegan women and 14.7% of raw vegan men who participated in the study were underweight. On the positive side, only 5% of the women and 6% of the men in this study were overweight or obese.[5]

Further research is warranted to understand the rates of underweight people in vegan populations and the resulting health consequences.

Generally, vegans with low body weight and muscle mass are making one of the mistakes described in lesson 14:11; they’re eating fruitarian diets, eating too few calories, or eating mostly flour products and processed foods.

If you’re a vegan who wants to build muscle mass, you should eat considerably more than 0.9 g protein per kg of body weight per day. Aim for 1.3 to 1.9 g/kg/day.

It’s entirely possible for you to build muscle with a vegan diet. However, if you are currently underweight, it may take a change in habits. You may need to eat more protein and more calories.

(Editor’s note: see Lesson 19: of our Mastery Program, written by vegan bodybuilder Robert Cheeke. It’s called “Nutrition for Vegan and Vegetarian Athletes”.)

Vegan athletes who restrict calories – or don’t eat enough legumes, tofu, tempeh, or other meat alternatives – are at risk for low protein intakes. On a raw diet, the equivalent is eating too few nuts, seeds, peas, sprouted lentils and sprouted mung beans.

You don’t need to combine specific plant proteins at each meal. However, it is important to consume good sources of protein at each meal. It can be helpful to add vegan protein powders such as hemp, rice, pea, pumpkin seed, or soy protein to smoothies.[6,7]

Research has established that plant protein is suitable for building and retaining muscle. In fact, a study of men who did resistance training found a soy-rich diet to be just as effective as a beef-rich diet for improving muscle strength and power.

For purposes of that study, either soy or beef was added to a vegetarian diet. In both cases, the men’s daily protein intake averaged 1.1 grams of protein per kilogram of body weight over twelve weeks.

Their program included resistance training, done at a gym three days per week.[21,22] Muscle mass increased equally and significantly in both the beef group and the soy group.

Researchers found no added benefit from components, such as creatine, that are present in meat but not in soy. They concluded that either soy or beef protein, combined with the right exercise, can delay muscle loss and increase muscle quantity, tone, and strength.[5,7,8]

Is the protein from plant sources the same to the body as animal protein, or less available?

The amount of fiber in a plant’s cell walls affects the “bioavailability” of its protein (i.e. how much of its protein you can absorb).

The proteins in most whole plant foods tend to be less bioavailable, in the range of 75% to 92%. As explained earlier in this lesson, vegans can offset this by consuming a little extra protein than the standard recommendation of 0.8 g protein/kg/day.

However, you can make plant foods more bioavailable with the food prep techniques you’ll discover in a moment.

Some believe that you adapt and absorb more from plants once you eliminate animal foods from your diet. However, there’s little research to document that.

Some plants have the same bioavailability of protein as animal products, which have no fiber. However, these are typically refined plant foods from which fiber has been removed, as shown in the following table.

Digestibility of protein in various foods.

Plant foods Digestibility %
White (refined) flour or bread 96
Soy protein isolate 95
Peanut butter 95
Tofu 93
Whole wheat flour or bread 92
Oatmeal 86
Lentils 84
Black, garbanzo, kidney,
and pinto beans
Animal products Digestibility %
Eggs 97
Milk, cheese 95
Beef, fish 94
Table data: [9-12]

At a glance, you might wonder if white bread (96% bioavailable) is a better source of protein than whole wheat bread (92% bioavailable). Or you might wonder if soy protein isolate (95% bioavailable) is a better choice than tofu or cooked beans. Yet the choice isn’t so simple.

Sure, processing plant foods increases the digestibility of their protein by removing fiber and other materials in cell walls. But it also strips these foods of valuable vitamins, minerals, and phytochemicals.[9-12]

Overall, the protein in the standard American diet (centered on animal products and refined carbohydrates) and Chinese diet (centered on white rice) has been rated as 96% digestible. The protein in Brazilian and Indian diets of rice and beans has been rated 78% digestible.[11,12]

Soaking and Sprouting Plant Proteins Makes Them More Bioavailable

The following food preparation techniques will help you absorb more protein. In fact, using these techniques can begin the digestive process.

For example, cooking beans and lentils — or sprouting buckwheat and peas — starts the breakdown of their proteins, resulting in increased absorption by your body.[14-17] When legumes and grains are soaked or sprouted, their proteins split into shorter chains of constituent amino acids. This essentially begins the digestion process.[14-15]

Soaking and sprouting nuts, seeds, and legumes also increases protein bioavailability. This is true whether you eat them raw or cook them after soaking.

For example, when you soak raw, dried, whole peas for 6 hours, their digestibility increases by 8%. If you soak them for 18 hours, it can increases by as much as 31%.

In other words, soaking and cooking peas increases the protein digestibility by 25% to 30%. Soaking and then pressure cooking results in an increase of 30% to 33%. That’s twice the protein digestibility of the exact same peas, when cooked without pre-soaking!

Scientists believe that soaking legumes activates plant enzymes, and this begins protein breakdown. So, when you soak legumes, you bring about the destruction of phytates and of trypsin inhibitors that can limit digestion.[14][18-20]

Allowing raw peas to sprout for 48 hours increases their protein digestibility by 25% to 28%. As a further benefit, studies have found that sprouting beans for six days removes most (70% to 100%) of the oligosaccharides that sometimes cause flatulence.[20-23]

Sprouting can further improve protein quality by slightly increasing the amount of essential amino acids, such as lysine.[23,24]

Blending fibrous vegetables (like kale) might make the amino acid lysine more available, but any claim beyond that is conjecture.



  1. [1] Mangels R, et al. The Dietitian’s Guide to Vegetarian Diets: Issues and Applications. Third Edition. Jones and Bartlett Learning. Sudbury MA. 2010.
  2. [2] Spencer EA, et al. Diet and body mass index in 38000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians and vegans. Int J Obes Relat Metab Disord. 2003;27(6):728–34.
  3. [3] Tonstad S, et al. Type of Vegetarian Diet, Body Weight and Prevalence of Type 2 Diabetes. Diabetes Care. 2009;32(5):791–6.
  4. [4] Davis B et al. Becoming Raw. The Book Publishing Co. 2010.
  5. [5] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  6. [6] Davis B et al. Becoming Vegan: Express Edition. The Book Publishing Co. 2013.
  7. [7] Haub MD et al. Beef and soy-based food supplements differentially affect serum lipoprotein-lipid profiles because of changes in carbohydrate intake and novel nutrient intake ratios in older men who resistive-train. Metabolism. 2005;54(6):769-74.
  8. [8] Haub MD et al. Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men. Am J Clin Nutr. 2002;76(3):511-7.
  9. [9] Davis B et al. Becoming Vegan: Comprehensive Edition. The Book Publishing Co. 2014.
  10. [10] Davis B et al. Becoming Vegan: Express Edition. The Book Publishing Co. 2013.
  11. [11] Mangels AR, Messina V, Messina M. The Dietitians Guide to Vegetarian Diets. Jones and Bartlett Learning Ltd. 2011.
  12. [12] Millward DJ, Layman DK, Tome D et al. Protein quality assessment: impact of expanding understanding of protein and amino acid needs for optimal health. Am J Clin Nutr. 2008;87(5):1576S-1581S.
  13. [13] World Health Organization/Food and Agriculture Organization/United Nations University. Expert Consultation. Protein and amino acid requirements in human nutrition. WHO Technical Report Series – 935. (World Health Organization/Food and Agriculture Organization). 2007.
  14. [14] Bishnoi S et al. Protein digestibility of vegetables and field peas (Pisum sativum). Varietal differences and effect of domestic processing and cooking methods. Plant Foods Hum Nutr. 1994;46:71-6.
  15. [15] Hernot DC et al. In vitro digestion characteristics of unprocessed and processed whole grains and their components. J Agric Food Chem. 2008;56:10721-6.
  16. [16] Oste RE. Digestibility of processed food protein. Adv Exp Med Biol. 1991;289:371-88.
  17. [17] Zia-ur-Rehman et al. The effects of hydrothermal processing on antinutrients, protein and starch digestibility of food legumes. Int. J. Food Science Technol. 2005;40:695–700.
  18. [18] Frias J et al. Evolution of trypsin inhibitor activity during germination of lentils. J. Agric Food Chem. 1995.43:2231-2234.
  19. [19] Ibrahim SS, et al. Effect of soaking, germination, cooking and fermentation on antinutritional factors in cowpeas. Nahrung. 2002;46:92-5.
  20. [20] Sathe SK et al. Effects of germination on proteins, raffinose, oligosaccharides, and antinutritional factors in the Great Northern beans (Phaseolus vulgaris L.). J Food Sci. 1983;48:1796-1800.
  21. [21] Chang KC et al. Effect of germination on oligosaccharides and nonstarch polysaccharidesin navy and pinto beans. J Food Science. 1989; 54(6):1615.
  22. [22] Oboh HA et al. Effect of soaking, cooking and germination on the oligosaccharide content of selected Nigerian legume seeds. Plant Foods Hum Nutr. 2000;55(2):97-110.
  23. [23] Chavan JK et al. Nutritional improvement of cereals by sprouting. Crit Rev Food Sci Nutr. 1989;28:401-37.
  24. [24] Chavan JK et al. Nutritional improvement of cereals by fermentation. Crit Rev Food Sci Nutr. 1989;28:349-400.

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