- Contrary to a widely held belief, proteins and all the essential amino acids are abundantly present in plant-based foods.
- Due to lower digestibility and different amino acid ratios, vegetable protein sources have sometimes been described as “inferior” to animal protein sources.
- Amino acid scores of plants are relatively lower compared to animal products (POA). Despite this, vegans can easily meet their essential amino acid requirements.
- This article in no way replaces the opinion of a medical nutritionist who should be contacted in case of doubt.
Canadian Nutrient File: CNF – A comprehensive database that tells us about the nutrients (macro-nutrients, vitamins, minerals, etc.) found in thousands of foods.
Dietary Protein and Amino Acids in Vegetarian Diets – A study establishing an appraisal of protein and amino acid intakes from different vegetarian diets. It builds on previous research on vegetarian and vegan populations.
CERIN : Besoins en protéines et en acides aminés & qualité des protéines alimentaires – A report from the Centre for Nutritional Research and Information. It provides information on recommended protein and amino acid intakes.
A warning: CERIN’s acronym is intentionally misleading. Behind its title as a research centre, it is a centre of propaganda.
Plant proteins in relation to human protein and amino acid nutrition – A study presenting the essential amino acids present in many plant proteins. It also reviews a list of myths and realities about the quality of plant proteins.
Among the general public and even in medical circles, meat is perceived as an essential source of nutrients. It is therefore generally accepted that to do without it would expose oneself to severe deficiencies, and proteins are obviously no exception to this rule.
But is it true ? Are the flesh and secretions of other animals really the only sources of proteins? Or can we, as humans, find protein of sufficient quality and quantity in plants?
Today, we observe that animal products are increasingly being decried for their deleterious impact on the environment and health, as well as for the ethical issues they raise. In this article, we will try to answer some of them as clearly as possible.
What are proteins for, and how much do we need them?
Proteins have important functions in the renewal of cells, bone matrix, skin, hair, nails and muscle tissue, to name but a few . They are therefore indispensable. They also participate in many physiological processes, for example in the formation of digestive enzymes, haemoglobin, hormones, etc. They are also involved in many other physiological processes.
According to nutritional recommendations, a minimum of 0.66 g of protein per kilogram of body weight is required daily . However, it is recommended to consume 0.83 g of protein per kilogram to ensure a certain margin of error.
In practice, a 70 kg person with average activity will therefore need at least 46 g of protein daily. With this level, the body will be able to function normally, but health organizations prefer, as a precaution, to recommend a mass of 58 g. For people who practice a high level of sporting activities, it may be appropriate to consume more protein. Proteins are involved in the repair of microtears in the muscles after physical exertion. These tears are both more important and more frequent as a result of training. Thus, the Centre for Nutritional Research and Information (CERIN) recommends a protein intake of 1.1 g/kg body weight per day for endurance sports enthusiasts (such as running) .
For sports aimed at maintaining or increasing muscle mass, the daily intake recommended by the CERIN varies between 1.3 and 2.5 g / kg. In view of the scientific literature on the subject, however, this last recommendation seems to be overestimated. Indeed, a systematic review of 49 studies involving more than 1800 people concluded that “protein intakes of more than ~1.6 g/kg/day do not contribute to an increase in muscle mass” .
There is therefore a priori no interest in exceeding these intakes, except for the energy intake provided by the surplus (1 g of protein provides 4 kilocalories).
As we have just seen what quantities of protein are necessary for us to function properly, we are now able to look at the vegan populations to see if they are in deficit in relation to these recommendations. To do this we will base ourselves on the work carried out by researchers François Mariotti and Christopher D. Gardner in their study “Dietary Protein and Amino Acids in Vegetarian Diets” . They draw up three tables gathering the declarative data collected during previous research.
Here is the first, examining more than 29,000 people based on their diets, as part of the EPIC-Oxford study. It shows that the average protein level of vegans is 0.99 g/kg body weight, well above the recommended 0.83 g.
The French study Nutrinet-Santé, with more than 100,000 participants, reports similar results. The proportion of protein in the diet of vegans represents 12.8% of their total caloric intake, with a level above 10% being considered an adequate protein intake.
The same applies to vegans in the Adventist Health Study 2, which includes 96,000 participants in the USA and Canada (see the following figure). The vegans in this study consume sufficient quantities of protein close to those of omnivores (71 g on average daily).
In addition, a 2014 study compared the nutritional scores of the diets of 1475 participants in the United States and England, distinguishing between those who were omnivorous (155), pesco-vegetarians (fish-eating; 145), semi-vegetarians (flexitarians; 498), vegetarians (573) and vegans (104). In this study, the foods eaten regularly by the participants were considered. The results suggest that although the participants’ vegan diet was associated with the lowest protein intake, it also received the highest nutrient scores; in comparison, the participants’ omnivorous diet received the lowest scores .
Indeed, the results of these studies are clear: there is no widespread deficiency in these large cohorts of people across the Western world. Protein recommendations are, on average, widely reached among vegans. In fact, it is noteworthy that vegans are closer to the official recommendations than people who have adopted other diets.
But then, if these people do not consume any animal products without developing a deficiency, where do they get their proteins?
Plant protein sources
The answer is quite simple : pretty much everywhere. Proteins are found in the five major food groups that make up a vegan diet: vegetables, fruits, grains, legumes and oilseeds, but they contain them in varying proportions.
Fruits and vegetables, for example, have little protein. On the other hand, more protein is found in other plants. As a result, cereals (wheat, rice, buckwheat, etc.) contain about 6 to 13% protein before cooking. For legumes (lentils, beans, soybeans, etc.), the number is between 18 and 26%, and finally between 15 and 19% for oilseeds (walnuts, peanuts, pistachios, hazelnuts, etc. ) .
In comparison, meats have an average protein content of about 25%. Eggs are around 13% and cheeses between 17 and 30%. Finally, a glass of milk provides the body with approximately 8g of protein .
Thus, we can see that there is no problem to find proteins in sufficient quantities in plants. But vegetable proteins definitely have a bad reputation. That is because even though they are present in quantity in the plant world, it is often considered that it is their quality that really poses a problem.
The problem of the quality of vegetable proteins
Michel Cymes, a general practitioner on the RTL radio in France, said about vegetarians that “vegetable proteins do not contain all the essential amino acids“. To understand what he is saying, we need to go deeper into the subject of proteins.
In reality our body does not need proteins as such, but the amino acids that make them up, because we do not have the capacity to use proteins as such. When we ingest food, our body breaks down proteins into amino acids that can be used by our body. Thus, proteins are made up of a total of 20 amino acids (AAs). Of these, 9 are called “essential”: this means that the body cannot synthesize them itself from other amino acids. They must therefore be provided by our diet.
These 9 essential amino acids (EAA) are lysine, leucine, isoleucine, tryptophan, methionine, valine, phenylalanine, threonine and histidine.
Thus, according to Michel Cyme’s sayings, plant proteins would be of “poor quality” because some AAs would be missing in their aminogram. But before going any further, it should be pointed out that all essential amino acids are indeed found in vegetable proteins.
For example, here is the aminogram of whole wheat pasta: we can see that all the EAAs are present. However, it is true that the proportions of EAAs in animal products are higher than those of most plants. It is therefore important to ask whether eating only plants implies that you will not meet your biological needs in EAAs
To define the quality of proteins, ingredients are given “scores” by calculating two scores: the PDCAAS (chemical score corrected for digestibility) and the DIAAS (digestible essential amino acid score). PDCAAS and DIAAS are two relatively similar methods of calculation. Here are their respective formulas: 
Without going into too much detail, the protein quality of a food is therefore evaluated by taking into account two parameters: the first is the ratio between, on the one hand, the quantity of EAAs contained in the protein, and on the other hand the reference requirements (in EAAs) of the human organism.
The requirements for each essential amino acid are, as an indication, grouped in the following table .
This table allows us to obtain the first parameter of our formula. The second parameter is the digestibility of the studied protein. The main difference between the two scores lies in the digestibility rate used in the calculation: PDCAAS uses fecal digestibility (measured at the outlet of the digestive tract), and DIAAS uses ileal digestibility (measured at the end of the small intestine).
Now that we have these two scores in mind, let’s take a look at their application to various foods:
|Food||PDCAAS (Varies between 0 and 1)||DIIAS|
|Wheat||0.42 – 51 ||20 – 54 [9,10]|
|Rice||0.42 ||0.37 |
|Black bean||0.75 |
|Egg||1 ||113 |
|Soy||0.91 – 1 [11,13]||0.90 – 0.91 |
|Vegetables||0.734 – 0.885 |
|Legumes||0.892 – 0.6958 |
Examination of these data shows that the values for plant proteins are indeed lower than for animal proteins. While legumes and vegetables have fairly high values, this is not the case for cereals such as wheat, for example. These lower values compared to animal products can be explained by 2 facts: firstly, vegetable proteins have a slightly lower digestibility overall than animal proteins. However, let’s not forget that proteins are not the only nutrients that are essential for our proper functioning. Indeed, in addition to proteins, plants are also made up of carbohydrates and fibres, which are mostly absent from animal products. This is a good thing, as we know that a large part of the population does not consume enough fibre .
But on a strictly protein level, these other nutrients hinder assimilation. They therefore slightly reduce the final absorption of proteins. In addition to this, the proportion of amino acids in plants and animal products is different. As said before, the aminogram of animal products is generally more optimal in relation to the needs of the human organism.
Let’s dig a little deeper: of the 9 essential amino acids, 2 are often cited as “limiting” within plant proteins. This means that one of the amino acids is present in small quantities compared to our needs. Cereals, for example, have relatively low levels of lysine. Legumes, on the other hand, often have a slight methionine deficiency.
This difference in digestibility and optimisation means that vegetable proteins, especially those with a highly limiting amino acid, have lower chemical scores (PDCAAS and DIAAS) than animal proteins, which is why proteins from vegan diets are sometimes considered “worse”. According to some, they may even cause amino acid deficiencies.
But is it true? Even if the aminogram of plants is different, does this mean that it does not provide for the needs of our bodies?
To answer this question, we will reconstruct the EAAs requirements cited in the previous table (daily needs in essential amino acids ). We can thus examine the requirements for lysine and methionine, as these are the two amino acids found in smaller quantities in cereals and pulses respectively. Thus, the daily lysine requirement is 30 mg per kilo of body weight, and 10 mg for methionine .
For the sake of example, we will voluntarily take a plant food considered “bad” from a protein point of view: wheat, with a PDCAAS of 0.42, which has lysine as a limiting amino acid. Let’s see if it is possible for an individual to meet his lysine needs by eating only whole wheat pasta.
First of all, the daily lysine requirement is 2.1 g for a 70 kg adult. Secondly, the faecal digestibility of wheat is 96%, i.e. 4% of the lysine contained in wheat will not be usable and lost during digestion . Therefore, 2.188 g of lysine from pasta must be ingested so that 2.1 grams of lysine are absorbed by the body after digestion. Knowing that 100 grams of whole-wheat pasta contains 324 mg of lysine, we deduce that this person will have to eat 675 grams (2349 kcal) of it during the day to meet his lysine needs. Remember that lysine is the limiting AA in wheat, and by definition, all other AA needs will be met by eating this amount.
Now let’s look at a legume, as legumes usually have methionine in AA-limiting. As with the lysine in whole wheat, let’s find out if it is possible to meet one’s needs by eating only one source of legume, by looking at the methionine intakes from chickpeas. Again, by consulting the data in the table we calculate that our adult must absorb 700 mg of assimilable methionine daily. Taking into account the ileal digestibility of chickpeas (74.6%) we must therefore ingest 938 mg of this source during the day [2,17].
Chickpeas, for example, contain 270 mg of methionine, so 350 grams (1313 kcal) per day should be eaten to ensure a good intake. Of course, for obvious reasons of culinary pleasure and other nutrient intake, no vegan would consume a single food during the day. But this proves that it is perfectly possible to meet your amino acid needs even by consuming only one type of food.
It should be emphasized that these calculations are simply made to demonstrate the good protein intake that can be provided by a vegetable diet. It is easy to imagine that eating only this could lead to other micronutrient deficiencies, or a risk of overweight. We also note that the results are much more favourable for chickpeas than for wheat. This is not abnormal because wheat is more a source of carbohydrates (energy) in our diet, whether meaty or not, than a source of protein.
This allows us to demystify another belief: that of the need for complementarity. According to some, it would be necessary to combine different sources of vegetable proteins during the same meal so that the aminograms complement each other. We can see, through our previous calculation, but also through other studies that this complementarity is not mandatory . A single source of vegetable protein can thus make it possible to provide all the EAAs, even in certain extreme (and unlikely) cases of monod diets.
And even when it is necessary, complementarity is very often instinctive or cultural; moreover, it has been achieved for millennia by different civilizations through their food customs.
Let’s look at some dishes as examples: Couscous is a mixture of semolina and chickpeas, and Mexican tacos are cooked with corn tortillas and red beans. In India, rice and lentils are often mixed, and hummus is made with chickpeas and tahini, a sesame cream, is added. Thus, since the dawn of time, humans have culturally combined legumes, grains and oilseeds. There is therefore no reason to worry today about complementarity between the different sources of vegetable proteins.
Finally, this does not concern all plants, because some plant foods are called “complete”: like most animal products, these do not have limiting amino acids . This is, for example, the case of quinoa or soybean.
What can we conclude from this ?
First of all, we have seen that, contrary to popular belief, proteins are indeed present in plants. This is particularly the case for legumes. Then, by analyzing the needs of the human organism as well as the EAA profiles of plants, we also found that it is easy to access the daily amount of protein. The thousands of vegans studied by the researchers are proof of this: they largely meet the recommendations shared by health organizations.
With this new knowledge at our disposal, we can reassure ourselves that ensuring protein intake is neither risky nor difficult. No need to be a nutrition expert or eat with a calculator in the corner of the table to balance your protein intake for a vegan. As long as he or she eats a varied and satisfying diet, there is no greater risk of developing a deficiency than a consumer of animal products.
- W.H. Organization, U.N. University, Protein and amino acid requirements in human nutrition, World Health Organization, 2007.
- D. Tomé, Besoins en protéines et en acides aminés & qualité des protéines alimentaires, Cholé-Doc. 48 (2008). https://sbssa.enseigne.ac-lyon.fr/spip/IMG/pdf/chole_doc_2009_-_besoin_en_prot_et_aa_et_qualite_des_prot.pdf.
- Centre de Recherche et d’information nutritionnelles, Besoin en protéines des sportifs (aspects quantitatif et qualitatif), (n.d.). https://www.cerin.org/actualites/besoin-en-proteines-des-sportifs-aspects-quantitatif-et-qualitatif/.
- R.W. Morton, K.T. Murphy, S.R. McKellar, B.J. Schoenfeld, M. Henselmans, E. Helms, A.A. Aragon, M.C. Devries, L. Banfield, J.W. Krieger, A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults, British Journal of Sports Medicine. 52 (2018) 376–384.
- F. Mariotti, C.D. Gardner, Dietary Protein and Amino Acids in Vegetarian Diets—A Review, Nutrients. 11 (2019) 2661.
- P. Clarys, T. Deliens, I. Huybrechts, P. Deriemaeker, B. Vanaelst, W. De Keyzer, M. Hebbelinck, P. Mullie, Comparison of nutritional quality of the vegan, vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diet, Nutrients. 6 (2014) 1318–1332.
- Government of Canada, Canadian Nutrient File (CNF), (n.d.). https://aliments-nutrition.canada.ca/cnf-fce.
- A. Nationale de Sécurité Sanitaire, CIQUAL french food composition database, (n.d.). https://ciqual.anses.fr/.
- I. Joye, Protein digestibility of cereal products, Foods. 8 (2019) 199.
- J.K. Mathai, Y. Liu, H.H. Stein, Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS), British Journal of Nutrition. 117 (2017) 490–499.
- S.M. Phillips, The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass, Nutrition & Metabolism. 13 (2016) 1–9.
- J.R. Hoffman, M.J. Falvo, Protein–which is best?, Journal of Sports Science & Medicine. 3 (2004) 118.
- G. Schaafsma, The protein digestibility–corrected amino acid score, The Journal of Nutrition. 130 (2000) 1865S–1867S.
- M.L. Suárez, A. Kizlansky, L. López, Assessment of protein quality in foods by calculating the amino acids score corrected by digestibility, Nutricion Hospitalaria. 21 (2006) 47–51.
- R. Clemens, S. Kranz, A.R. Mobley, T.A. Nicklas, M.P. Raimondi, J.C. Rodriguez, J.L. Slavin, H. Warshaw, Filling America’s fiber intake gap: summary of a roundtable to probe realistic solutions with a focus on grain-based foods, The Journal of Nutrition. 142 (2012) 1390S–1401S.
- G. Rizzo, L. Baroni, Soy, soy foods and their role in vegetarian diets, Nutrients. 10 (2018) 43.
- S. Kashyap, A. Varkey, N. Shivakumar, S. Devi, R. Reddy B H, T. Thomas, T. Preston, S. Sreeman, A.V. Kurpad, True ileal digestibility of legumes determined by dual-isotope tracer method in Indian adults, The American Journal of Clinical Nutrition. 110 (2019) 873–882.
- V.R. Young, P.L. Pellett, Plant proteins in relation to human protein and amino acid nutrition, The American Journal of Clinical Nutrition. 59 (1994) 1203S–1212S.