The recommended daily allowance (RDA) for protein for adults is 0.8 grams per kilogram of bodyweight per day. This means that a 70kg person needs to eat 56g of protein each day in order to meet this recommendation (70 x 0.8 = 56).
The RDA for protein was established using nitrogen balance studies1. These experiments monitor the amount of nitrogen consumed and excreted under controlled conditions. Since nitrogen is only found in proteins, it is assumed that a negative nitrogen balance is indicative of a catabolic state (a loss of protein); and zero net losses suggests that the body is obtaining sufficient protein. 0.8g/kg/d is thought to be the minimum amount of protein (virtually all) adults require to avoid net nitrogen losses and thus maintain lean mass.
Many nutrition and sport scientists with an interest in protein believe that the RDA underestimates the amount of protein required to maintain lean body mass. But as it stands, the RDA is still used by the World Health Organisation and most medical and dietetic establishments all over the world.
Is it given that vegans will reach the RDA?
It's often said that vegans will automatically meet the RDA for protein provided that they consume a sufficient amount of calories from a variety of plant-based foods. There is an element of truth to this: a eucaloric animal-free diet based on a variety of plant-based items – including protein rich foods – will most likely provide sufficient amounts of protein to meet (or exceed) the RDA. But an energy adequate animal-free diet could conceivably supply less than the RDA for protein if it's low in protein-rich foods.
Moreover, some vegans will not be eating enough calories to maintain their bodyweight (whether due to intentional calorie restriction, poor appetite, poor food choices etc.). Being in a calorie deficit increases the likelihood of failing to meet the RDA, especially if vegans are not cognisant of protein when planning their meals. Furthermore, nitrogen balance studies were conducted on individuals that were eating a maintenance diet: being in a calorie deficit may increase our requirement for protein (I'll return to this topic a little later).
A recent systematic review of observational and interventional studies indicates that vegans consume the lowest amount of protein (compared to vegetarians and meat eaters)2. While vegans on aggregate seem to consume at or above 0.8g/kg/d, it appears that a significant minority do not:
- A study based on the EPIC-Oxford cohort found that 16.5% of vegan males and 8.1% of vegan females consumed less than 0.6g/kg/d3.
- A Germany cross-sectional study found that more than 30% of vegan males and more than 40% of vegan females failed to reach 0.8g/kg/day4.
- 27% of vegans failed to eat above 10% of their calories from protein in a French cross-sectional study5.
- A small Slovenian cross-sectional study found that 31% of vegans failed to reach the 0.8g/kg/day30.
On the basis of the above, it seems clear that vegans need to be “protein-aware” to some extent in order to reliably meet or exceed the RDA for protein.
Is the RDA sufficient for vegans?
Plant-based sources of protein are usually considered “lower quality”. This is partly due to the presence of so-called anti-nutritional factors (such as trypsin-inhibitors, tannins, phytic acid) which seem to inhibit the digestion of protein6. Furthermore, fibre also seems to impair protein digestion (e.g., there is evidence showing that de-hulling legumes appears to improve protein quality7,8). In addition to lower digestibility, plant-based sources of protein typically exhibit lower levels of essential amino acids (building blocks of protein), especially lysine, methionine and cystine: this can be seen in the illustration below (taken from the book Vegetarian and Plant-Based Diets in Health and Disease Prevention9)
The lower digestibility and less favourable essential amino acid profiles of plant-based sources of protein are reflected in lower Digestible Indispensable Amino Acid Score (DIAAS) values. These values are usually obtained by testing foods on non-human animals and as such we can doubt the relevance of the results to some extent. Nonetheless, I think it's uncontroversial to say that most plant-based foods are of lower protein quality.
It is arguably surprising that the meta-analysis upon which the RDA was based, did not find plant protein to be inferior to animal protein in relation to achieving nitrogen balance1. However, it's worth noting that several of the studies relied on soy protein isolates/concentrates, which are thought to be roughly equivalent to animal protein in terms of protein quality. Moreover, participants consumed at least some animal protein in most of the test conditions and this may have had some bearing on nitrogen balance. Conceivably, consuming the RDA for protein via an animal-free diet that relies on lower quality protein sources may result in greater susceptibility to a negative nitrogen balance. Indeed, a recent study of older adults found that a meal that included red meat led to a considerably greater anabolic response in comparison to a protein-matched meal based on whole plant foods31.
For vegans eating 0.8g/kg/d, it's prudent to include some higher quality protein sources. This includes soy protein and other refined sources such as mycoprotein, seitan, protein powders etc. At this level of protein intake, it's probably also wise to combine legumes with grains due to their complementary amino acid profiles. But I suspect that most vegans in developed countries eat a variety of foods and therefore usually quite naturally obtain a good balance of amino acids.
Is the RDA optimal?
I've noticed that many vegans seem to assume that the RDA for protein is an estimate of the optimal intake for health outcomes: it's not. As stated earlier, the RDA is the minimum amount of protein required for most adults to maintain nitrogen balance (and thus avoid protein losses).
There are good reasons for thinking that protein intakes above the RDA are superior for certain health outcomes.
The benefits of protein intakes above the RDA
There is a considerable amount of evidence suggesting that eating higher protein diets reduces the risk of fractures and improves bone mineral density (BMD). BMD is a measure of the density of minerals in the bone; generally speaking, higher BMD is considered to represent stronger bones which are less prone to fractures.
- A 2017 meta-analysis of prospective cohort studies found that protein intakes above the RDA were inversely associated with hip fractures. Furthermore, protein intakes above the RDA correlated with smaller BMD losses at most sites10.
In older adults:
- A 2019 meta-analysis of four prospective cohort studies indicates that higher protein intake reduces the risk of hip fractures in older adults11. The same paper showed positive trends for femoral neck and total hip BMD with high protein consumption.
- A 2018 osteoporosis expert consensus paper concluded that: “In older people with osteoporosis, higher protein intake (≥0.8-g/kg body weight/day, i.e., above the current RDA) is associated with higher BMD, a slower rate of bone loss, and reduced risk of hip fracture, provided that dietary calcium intakes are adequate”12.
Muscle mass and strength
The RDA may be enough to preserve lean mass in adults eating a maintenance diet and not practising resistance training13. But this level of intake is suboptimal in terms of facilitating adaptions to exercise: it's well-established that intakes above the RDA optimises increases in strength and muscle in response to exercise 13, 14, 15.
Due to lower protein quality as well as lower total protein intake, plant-based diets may often be less anabolic compared to omnivorous diets. However, any inferiority in terms of anabolism seems to become largely – if not wholly – irrelevant when eating a higher protein diet. A seminal study has shown that habitual vegans consuming twice the RDA (1.6g/kg/d) experienced the same benefits in terms of muscle and strength adaptations to exercise compared to habitual omnivores consuming the same level of protein28. Furthermore, this result is in harmony with a meta-analysis of clinical trials which found that ~1.6 g/kg/day is sufficient for healthy adults and intakes above this level didn't appear to provide further benefits with respect to optimising muscle and strength in response to resistance training29.
Because of the numerous benefits of resistance training, it stands to reason that everyone should be lifting weights (if feasible). To get the most out of this, protein intakes above the RDA are highly advisable.
Higher protein diets protect lean mass during weight loss
The nitrogen balance studies which were used as the basis for the RDA were performed on participants eating maintenance diets1. However, clinical trials have shown that protein intakes above 0.8g/kg/d help to preserve lean mass in those in a negative energy balance. In other words, individuals reducing their caloric intake to lose fat mass, should consume diets above the RDA in in order to reduce unwanted losses of fat-free mass (particularly muscle mass).
Better function in older adulthood
Older adults seem suffer from “anabolic resistance”; meaning that in order to maintain / develop muscle mass, a greater preponderance of protein (or essential amino acids) is required16. It's been suggested that 1-1.3g/kg/day may be a more suitable target for healthy older adults17,18. While exercise appears to be the most important protective factor in relation to avoiding sarcopenia and the concomitant loss of function19; a higher protein diet may be especially important for older adults when it comes to optimising adaptations to exercise. Furthermore, some observational research indicates that higher protein intakes among older adults may be associated with greater muscle mass & strength; as well as a lower risk of functional impairment regardless of activity levels20,21.
High protein diets and longevity
Higher protein diets appear to be superior for muscle, strength and bone health; this may ultimately translate into better function (especially in older adulthood). But many have expressed concerns about the potential drawbacks of higher protein intakes; especially in relation to longevity. A lot of research suggests that low protein diets may improve healthspan and lifespan in non-human animals22. It's not clear, however, to what extent protein restriction is recommendable for humans. A recent meta-analysis of prospective cohort studies for example found that higher protein diets are associated with a lower risk of all-cause mortality23. Admittedly, animal protein is consistently associated with health problems relative to plant protein23,24. In my estimation, this is likely due to the fact that animal protein often comes with saturated fat/cholesterol and is devoid of fibre; rather than a result of the protein itself. Regardless, since plant protein isn't linked to health problems, I fail to see why healthy individuals should restrict protein from plant-based sources for an unproven benefit; especially when the advantages of higher protein intakes in terms of anabolism are well-supported with evidence.
High protein diets and chronic kidney disease
Randomised controlled trials indicate that higher protein intakes among healthy people does not negatively affect kidney function25. But those already with chronic kidney disease should discuss the safety of adopting a high protein diet with their physician since there is evidence suggesting that lower protein diets may slow down the progression of this illness26.
However, it is yet to be elucidated whether it's the protein per se which accelerates progression of kidney disease; or whether higher protein is a mere marker of diet quality. Indeed, legumes, nuts and low-fat dairy appear to reduce the risk of kidney disease; whereas red meat has been linked to increased risk27.
Protein recommendations for vegans
I recommend consuming around 1.2-1.6g/kg/day for those on an animal-free diet. This can be achieved by making protein-rich foods the centerpiece of your meals. When eating this amount of protein, "protein combining" is redundant as you will obtain more than enough essential amino acids. Arguably, legumes and traditional soy products are the best options, since these foods have been well-studied and are inversely associated with health problems. But there are plenty of other options to consider such as: mycoprotein, seitan, peanut butter powder (sugar-free), TVP + more.
Here are some examples of animal-free high protein meals:
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1. Rand, W.M., Pellett, P.L. and Young, V.R., 2003. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. The American journal of clinical nutrition, 77(1), pp.109-127.
2. Neufingerl, N. and Eilander, A., 2021. Nutrient Intake and Status in Adults Consuming Plant-Based Diets Compared to Meat-Eaters: A Systematic Review. Nutrients, 14(1), p.29.
3. Sobiecki, J.G., Appleby, P.N., Bradbury, K.E. and Key, T.J., 2016. High compliance with dietary recommendations in a cohort of meat eaters, fish eaters, vegetarians, and vegans: results from the European Prospective Investigation into Cancer and Nutrition–Oxford study. Nutrition Research, 36(5), pp.464-477.
4. Waldmann, A., Koschizke, J.W., Leitzmann, C. and Hahn, A., 2003. Dietary intakes and lifestyle factors of a vegan population in Germany: results from the German Vegan Study. European journal of clinical nutrition, 57(8), pp.947-955.
5. Allès, B., Baudry, J., Méjean, C., Touvier, M., Péneau, S., Hercberg, S. and Kesse-Guyot, E., 2017. Comparison of sociodemographic and nutritional characteristics between self-reported vegetarians, vegans, and meat-eaters from the NutriNet-Santé study. Nutrients, 9(9), p.1023.
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7.. Devi, S., Varkey, A., Sheshshayee, M.S., Preston, T. and Kurpad, A.V., 2018. Measurement of protein digestibility in humans by a dual-tracer method. The American journal of clinical nutrition, 107(6), pp.984-991.
8. Siegert, W., Ibrahim, A., Link, W., Lux, G., Schmidtke, K., Hartung, J., Nautscher, N. and Rodehutscord, M., 2022. Amino acid digestibility and metabolisable energy of spring and winter faba beans grown on two sites and effects of dehulling in caecectomised laying hens. Journal of the Science of Food and Agriculture, 102(3), pp.920-930.
9. Mariotti F. Plant protein, animal protein, and protein quality. InVegetarian and plant-based diets in health and disease prevention 2017 Jan 1 (pp. 621-642). Academic Press.
10. Wallace, T.C. and Frankenfeld, C.L., 2017. Dietary protein intake above the current RDA and bone health: a systematic review and meta-analysis. Journal of the American College of Nutrition, 36(6), pp.481-496.
11. Groenendijk, I., den Boeft, L., van Loon, L.J. and de Groot, L.C., 2019. High versus low dietary protein intake and bone health in older adults: a systematic review and meta-analysis. Computational and structural biotechnology journal, 17, pp.1101-1112.
12. Rizzoli, R., Biver, E., Bonjour, J.P., Coxam, V., Goltzman, D., Kanis, J.A., Lappe, J., Rejnmark, L., Sahni, S., Weaver, C. and Weiler, H., 2018. Benefits and safety of dietary protein for bone health—an expert consensus paper endorsed by the European Society for Clinical and Economical Aspects of Osteopororosis, Osteoarthritis, and Musculoskeletal Diseases and by the International Osteoporosis Foundation. Osteoporosis International, 29(9), pp.1933-1948.
13. Hudson, J.L., Wang, Y., Bergia III, R.E. and Campbell, W.W., 2020. Protein intake greater than the RDA differentially influences whole-body lean mass responses to purposeful catabolic and anabolic stressors: a systematic review and meta-analysis. Advances in Nutrition, 11(3), pp.548-558.
14. Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., Henselmans, M., Helms, E., Aragon, A.A., Devries, M.C., Banfield, L., Krieger, J.W. and Phillips, S.M., 2018. 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(6), pp.376-384.
15. Nunes, E.A., Colenso?Semple, L., McKellar, S.R., Yau, T., Ali, M.U., Fitzpatrick?Lewis, D., Sherifali, D., Gaudichon, C., Tomé, D., Atherton, P.J. and Robles, M.C., 2022. Systematic review and meta?analysis of protein intake to support muscle mass and function in healthy adults. Journal of Cachexia, Sarcopenia and Muscle.
16. Endo, Y., Nourmahnad, A. and Sinha, I., 2020. Optimizing skeletal muscle anabolic response to resistance training in aging. Frontiers in physiology, 11, p.874.
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18. Rafii, M., Chapman, K., Elango, R., Campbell, W.W., Ball, R.O., Pencharz, P.B. and Courtney-Martin, G., 2015. Dietary protein requirement of men> 65 years old determined by the indicator amino acid oxidation technique is higher than the current estimated average requirement. The Journal of nutrition, 146(4), pp.681-687.
19. Talar, K., Hernández-Belmonte, A., Vetrovsky, T., Steffl, M., Ka?amacka, E. and Courel-Ibáñez, J., 2021. Benefits of resistance training in early and late stages of frailty and sarcopenia: a systematic review and meta-Analysis of randomized controlled studies. Journal of Clinical Medicine, 10(8), p.1630.
20. Yuan, M., Pickering, R.T., Bradlee, M.L., Mustafa, J., Singer, M.R. and Moore, L.L., 2021. Animal protein intake reduces risk of functional impairment and strength loss in older adults. Clinical Nutrition, 40(3), pp.919-927.
21. Bradlee, M.L., Mustafa, J., Singer, M.R. and Moore, L.L., 2018. High-protein foods and physical activity protect against age-related muscle loss and functional decline. The Journals of Gerontology: Series A, 73(1), pp.88-94.
22. Mirzaei, H., Suarez, J.A. and Longo, V.D., 2014. Protein and amino acid restriction, aging and disease: from yeast to humans. Trends in Endocrinology & Metabolism, 25(11), pp.558-566.
23. Naghshi, S., Sadeghi, O., Willett, W.C. and Esmaillzadeh, A., 2020. Dietary intake of total, animal, and plant proteins and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies. bmj, 370.
24. Chen, Z., Glisic, M., Song, M., Aliahmad, H.A., Zhang, X., Moumdjian, A.C., Gonzalez-Jaramillo, V., van der Schaft, N., Bramer, W.M., Ikram, M.A. and Voortman, T., 2020. Dietary protein intake and all-cause and cause-specific mortality: Results from the Rotterdam Study and a meta-analysis of prospective cohort studies. European journal of epidemiology, 35(5), pp.411-429.
25. Devries, M.C., Sithamparapillai, A., Brimble, K.S., Banfield, L., Morton, R.W. and Phillips, S.M., 2018. Changes in kidney function do not differ between healthy adults consuming higher-compared with lower-or normal-protein diets: a systematic review and meta-analysis. The Journal of nutrition, 148(11), pp.1760-1775.
26. Rhee, C.M., Ahmadi, S.F., Kovesdy, C.P. and Kalantar?Zadeh, K., 2018. Low?protein diet for conservative management of chronic kidney disease: a systematic review and meta?analysis of controlled trials. Journal of cachexia, sarcopenia and muscle, 9(2), pp.235-245.
27. Haring, B., Selvin, E., Liang, M., Coresh, J., Grams, M.E., Petruski-Ivleva, N., Steffen, L.M. and Rebholz, C.M., 2017. Dietary protein sources and risk for incident chronic kidney disease: results from the Atherosclerosis Risk in Communities (ARIC) Study. Journal of Renal Nutrition, 27(4), pp.233-242.
28. Hevia-Larraín, V., Gualano, B., Longobardi, I., Gil, S., Fernandes, A.L., Costa, L.A., Pereira, R.M., Artioli, G.G., Phillips, S.M. and Roschel, H., 2021. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: a comparison between habitual vegans and omnivores. Sports Medicine, 51(6), pp.1317-1330.
29. Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., Henselmans, M., Helms, E., Aragon, A.A., Devries, M.C., Banfield, L., Krieger, J.W. and Phillips, S.M., 2018. 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(6), pp.376-384.
30. Bogataj Jontez, N., Kenig, S., Šik Novak, K., Petelin, A., Jenko Pražnikar, Z. and Mohorko, N., 2023. Habitual low carbohydrate high fat diet compared with omnivorous, vegan, and vegetarian diets. Frontiers in Nutrition, 10, p.572.