Recently there has been a surge of interest in plant-based diets following the release of popular documentaries, advocation from well-known celebrities, the rise of more plant-centered dietary guidelines, and the rapidly increasing prevalence of plant-based alternatives to popular foods. Subsequently, there has also been a swath of questions, concerns, and proclamations to follow; ranging from honest inquisitions and concerns based on a lack of knowledge on the subject to rampant, egregious misinformation (coming from both those advocating for and against these diets). While there is a large selection of popular topics that deserve attention, this specific article will serve to hone in on questions, concerns, and misinformation pertinent to one of the most frequently discussed; protein. Hopefully in doing so it will serve to clear up the confusion for many of those wishing to adopt a mostly or entirely plant-based diet.
As a brief preface, it should be mentioned that despite pervasive claims that plant-based diets are insufficient (or even harmful) to overall health and sports performance, they can easily be formulated to support athletic endeavors, be nutritionally adequate, and provide health benefits; conferring protection against and potentially serving as adjunct treatments for chronic conditions such as hypertension, cardiovascular disease, and type 2 diabetes. Multiple high quality, long term prospective cohorts have demonstrated those who followed more plant-based diets have decreased risk of death from all causes and experience lower rates of cardiovascular disease, diabetes, and many types of cancers¹-⁵.
In accordance with this, the Academy of Nutrition and Dietetics (the world’s largest organization of food and nutrition professionals) stated such in their position paper on vegetarian diets⁶. They remark that well-planned (an important caveat that applies to every healthy diet) vegetarian and vegan diets are appropriate for individuals during all stages of the life cycle. They mention a few nutrients of concern, such as vitamin B12, D (depending on your latitude and exposure to sunlight), iodine, omega 3 fatty acids, and zinc, yet emphasize that requirements for each can easily be reached with appropriate consideration. These nutrients can be supplied through supplementation (in the case of B12 and vitamin D), consumption of fortified foods (or salt in the case of iodine), and inclusion of a variety of foods naturally rich in them (legumes, some whole grains, and potatoes for zinc and flax, chia, and hemp seeds or walnuts for omega 3).
“It is the position of the Academy of Nutrition and Dietetics that appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes.”
“Vegetarians and vegans are at a reduced risk of certain health conditions, including ischemic heart disease, type 2 diabetes, hypertension, certain types of cancer, and obesity.”
General nutritional adequacy and impacts of plant-based diets on general health aside, this article will focus on addressing common questions and dispelling myths surrounding protein sources, along with their quality, the quantity appropriate for various individuals, and a few other noteworthy considerations.
Among those most hesitant to adopt a more plant-based diet are athletes and generally active individuals, especially given the constant emphasis on high protein intake to support optimal performance. Along with this, they are also met with repeated claims that plants lack “quality” protein and vegans/vegetarians require substantially more than omnivores to improve strength, lean body mass (LBM), and overall exercise capacity. In spite of this, there are no publications clearly establishing significant differences in hard outcomes (especially strength, lean body mass, and endurance performance) suggesting that those following a mostly or entirely plant-based diet need to consume much more protein than omnivores in order to reach an intake of total protein and essential amino acids conducive to the aforementioned endpoints. With just some basic knowledge and a varied diet, a sufficient intake is easily achievable, although that discussion will be continued later on. Given these points, it should be relatively clear that consuming foods of animal origin is not an inherent requirement for building appreciable amounts of muscle, gaining strength, and improving overall physical capabilities. Unfortunately, one can only wish things were that simple. As with many topics in nutritional science, discussions around plant-based protein are fraught with a myriad of sensationalized, misinformed, contradictory, or downright false claims, causing those who attempt to find the correct information themselves to be frequently left even more confused. As such, an in-depth discussion of the subject will follow, in the hopes of providing some clarity among the murky waters of misinformation all too common in the present day.
Before delving into the research, it is paramount to enumerate the common false perceptions surrounding plant-based sources of protein; namely that they aren’t “complete”, that they have a poor digestibility preventing them from supporting muscle growth and sports performance, and that athletes need to consume well over the recommended intake (ranging from 1–1.6 g/kg or higher depending on the discipline/goal in question) in order to achieve an adequate intake of certain essential amino acids (EAAs). Of particular importance is the EAA leucine, commonly acknowledged as the main stimulus for muscle protein synthesis, an important process in the accretion of muscle tissue and strength. As touched on previously, these are either misconceptions or are not based on outcome data, but rather almost exclusively on assumptions drawn from mechanistic studies observing changes in surrogate biomarkers. The following few sections will elaborate upon the origin and the validity of these particular claims, consulting the available evidence for each.
Are Plant-Based Proteins “Incomplete”?
As pictured above, even while mentioning the notion that individuals only consuming plant-based sources of protein can’t build muscle is incorrect, this fitness website still repeats the myth asserting these foods don’t contain all the essential amino acids. While this statement is recognized by most dietitians and other nutrition professionals as false, it is still prevalent on many popular websites, among the lay public, and even on food labels.
In reality, plant-based foods have all of the required EAAs, the only difference being that they are present in different proportions compared to animal products (most notably some contain smaller amounts of lysine, leucine, and methionine relative to the other amino acids). Funnily enough, the only food that doesn’t contain all the essential amino acids is actually gelatin, which is derived from the collagen found in animals’ skin, bones, ligaments, and tendons. All of this is resoundingly clear upon simply consulting a food-nutrient database with information on the amino acid composition of various foods, such as the USDA’s FoodData Central (accessible here).
Taking this into consideration, as long as a plant-based diet is balanced and contains protein from a variety of food sources (legumes, nuts/seeds, whole grains, tubers, fruits, and vegetables, along with options such as seitan, meat analogs, and protein powders if desired), getting these essential amino acids shouldn’t be an issue in the slightest. Additionally, the former have been consistently shown to significantly reduce the risk of a wide variety of chronic diseases and other adverse health outcomes⁷-¹⁴. This is not to say that there aren’t sources of animal protein that can be part of a diet that supports long term health (as are even discussed in many of the publications cited above), but this article is intended to provide information and assistance to those looking to adopt mostly or entirely plant-based diets. Furthermore, in contrast, if you eat a plant-based diet consisting of Oreos, chips, juice, and other processed snacks, or adopt a fad version of one (fruitarian, raw, very low fat, etc.) you may run into a problem getting sufficient protein, not to mention your health will almost certainly suffer as well. Similar to how any generally healthy diet requires a slight bit of planning to ensure adequate nutrient intake, the same applies to those formulated around plant-based foods. Underscoring the extent to which the misinformation on this topic has permeated among the public, and re-emphasizing the points covered here, the Academy of Nutrition and Dietetics’ position paper acknowledges the following:
The terms complete and incomplete are misleading in relation to plant protein. Protein from a variety of plant foods, eaten during the course of a day, supplies enough of all indispensable (essential) amino acids when caloric requirements are met.⁷ The regular use of legumes and soy products will ensure an adequate protein intake for the vegetarian, as well as providing other essential nutrients.
Similarly, a recent review from Stanford Prevention Research Center’s Department of Medicine discusses many of these concerns in-depth and highlights how over-exaggerated claims pertinent to amino acid insufficiency of plant-based diets are, indicating that there is a dearth of evidence suggesting such an issue even exists in first world countries with a reliable food supply¹⁵.
“ In this review, we examine the protein and amino acid intakes from vegetarian diets followed by adults in western countries and gather information in terms of adequacy for protein and amino acids requirements, using indirect and direct data to estimate nutritional status. We point out that protein-rich foods, such as traditional legumes, nuts and seeds, are sufficient to achieve full protein adequacy in adults consuming vegetarian/vegan diets, while the question of any amino acid deficiency has been substantially overstated.”
“It is commonly, although mistakenly, thought that the amino acid intake may be inadequate in vegetarian diets. As we and others have argued, the amounts and proportions of amino acids consumed by vegetarians and vegans are typically more than sufficient to meet and exceed individual daily requirements, provided a reasonable variety of foods are consumed and energy intake needs are being met.”
For a simple, detailed, and understandable discussion of this topic (along with many others related to nutrition), and a sample comparison of the amino acids profiles of various plant and animal-based foods, those who are interested in learning more can watch this video that is a part of a series on protein by Gil Carvalho, MD PhD. Alternately, for a far more in-depth discussion of this topic, it is worth consulting the “Plant Protein, Animal Protein, and Protein Quality” chapter of François Mariotti’s book Vegetarian and Plant-Based Diets in Health and Disease Prevention¹⁶. Also found in the same chapter is this comprehensive figure depicting the amino acid proportions of various food sources pictured below.
When comparing common plant and animal-based sources of protein as Gil does in his video and Mariotti in his book, one will quickly discover they are fairly similar, and that regular-sized servings of plant-based foods will provide appreciable amounts of the EAAs. Soy and other legumes tend to fare very well against many sources of animal protein, only having very minor differences in a select few amino acids, namely methionine and cysteine, clearly illustrated in the graphic above). Furthermore, one commonly consumed meat substitute, seitan (which is made from vital wheat gluten and/or chickpea/soy flour, nutritional yeast, and various seasonings), actually has a macronutrient and amino acid profile very similar to chicken. Given all this information, hopefully it has become fairly clear that this common misconception about plant-based sources of protein being “incomplete” is far from the truth.
A Brief Discourse on the Evaluation of Evidence Supporting a Claim
Before continuing on to a few other common assumptions about plant-based proteins, it is important to emphasize a crucial point about epistemology with respect to fitness, health, nutrition, and medical research. While mechanistic and animal model research can be important for formulating and testing a nascent hypothesis, as a general rule results from human-based outcome studies are far more reliable and relevant. Such outcome data, be it from well-designed observational cohort (preferably prospective) studies or controlled trials, supersedes speculations arising from animal and mechanistic studies. This is the premise of the evidence hierarchy (seen below), a heuristic for the proper assessment of various forms of evidence supporting or opposing a theory. Unfortunately, there are many individuals even within the fields of nutrition, medicine, and fitness that fail to appreciate or understand these crucial considerations. Henceforth, fairly often this results in many of them positing claims about certain subjects that may be true in the lower tiers of evidence, but do not actually reflect what is seen in humans. These lower tiers are notoriously inconsistent with respect to their applicability to human outcomes, a trend that is highly apparent in the very low success rates of disease treatment in human clinical trials that showed promise in animal models¹⁷.
These concerns are especially relevant to the upcoming discussion of claims surrounding plant-based proteins, as many of them are based on low quality (mechanistic/animal model) evidence; but upon review the findings in humans from the higher tiers of the hierarchy (RCTs, prospective cohorts, and/or meta-analyses of the two) oppose the implications stemming from the former.
PDCAAS (Protein Digestibility-Corrected Amino Acid Score) & DIAAS (Digestible Indispensable Amino Acid Score)
PDCAAS and DIAAS are the two most commonly discussed scoring systems designed to assign values to various sources of dietary protein that represent their quality. The respective scores are based upon assessments of the amino acid composition of various protein sources and how well they are digested. Both are frequently used to assert that there are major differences between plant and animal-based protein sources, implying some sort of inferiority of plant-based proteins. However, most individuals don’t possess a thorough understanding of what the scoring systems entail, how they are calculated, and what the actual implications for humans are. PDCAAS has quite a few openly acknowledged limitations, and consequently there has been a recent shift towards a preference for DIAAS, so that will be the primary focus of this discussion.
The main advantage provided by the DIAAS method is that it determines the ileal digestibility of each individual amino acid instead of just the fecal digestibility of the entire protein, providing a better assessment of the overall bioavailability of the amino acids from the protein source in question, and preventing falsely overexaggerated values resulting from bacterial assimilation of amino acids beyond the ileum of the small intestine. Furthermore, PDCAAS was primarily carried out in rats, which have different amino acid requirements from humans. Alternatively, DIAAS is carried out in pigs, which have more similar requirements. The intention of these scoring systems is to assess the specific digestibility of amino acids from complex food sources in isolation as to highlight which foods may serve best to quell protein malnutrition in individuals with limited food supplies, in certain clinical situations, with chronic diseases altering normal metabolism, and so on. For example, DIAAS scores can range from 0 to over 100, with a value over 100 indicating that if that single food was used to meet daily protein recommendations (in g/kg), it could satisfy all the individual essential amino acid requirements. While some foods may have scores under 100, mixed meals consumed throughout the day that contain multiple sources of protein and supply differing proportions of EAAs can easily propel the meal’s score over 100. Since DIAAS values are also additive, they allow for such a calculation to be made following a specific formula. Therefore, taking values for foods in isolation for anything other than instances where they are the sole source of nutrition is erroneous and suggests a misunderstanding of the scoring system¹⁸. For a thorough discussion of the issues discussed here, in addition to a few others inherent to DIAAS, one can read Craddock et al.’s recent review on the scoring system with specific attention to plant-based diets, which strongly concludes with the following:
If protein quality must be assessed, the PDCAAS remains the most suitable tool for use in Western adults adhering to a plant-based dietary pattern. As our understanding of plant-based nutrition has improved however, it has become increasingly apparent that emphasizing protein quality in developed nations is unproductive, influencing food selection with irrelevant metrics rather than more important dietary factors and truly prevalent nutritional shortcomings (i.e., fiber). Pervasive use of DIAAS and food selection based on this score is thus futile at best and harmful at worst.
Even with this type of scoring system not being particularly relevant to most people’s current situation or accurately reflecting impacts on hard endpoints, some of the differences between common plant and animal-based dietary sources of protein aren’t as substantial as many make them out to be. In addition to the minor amino acid composition differences mention previously, the Stanford paper discussed earlier discusses the topic of protein digestibility, and mentions a publication¹⁹ demonstrating that the more precise data in humans shows very little actual differences in ileal-digestibility (one of the main components of the DIAAS score) of a few common plant and animal-based sources of protein.
The more precise data collected so far in humans, assessing real (specific) oro-ileal nitrogen digestibility, has shown that the differences in the digestibility between plant and animal protein sources are only a few percent, contrary to historical findings in rats or determinations using less precise methods in humans.
In addition, factors that may elicit slight reductions in protein digestibility of other plant-based sources of protein are covered, such as anti-nutritional factors and plant cell walls. This further elucidates the fact that despite differences in some protein sources being more notable, the scores calculated using digestibility data derived from animal feeding studies (i.e., PDCAAS and DIAAS) may not necessarily represent the true values in humans given the sources are typically fed to the animals whole and raw, where these factors are maximized. To be fair, this is exactly the type of speculation that one should hope to avoid relying on, so it shouldn’t hold much weight without more empirical data. Nonetheless, a recent study designed to determine unknown true ileal digestibility values of certain legumes in humans did reflect how some of these factors may indeed affect their scores, but not to an excessive degree. It was revealed that chickpeas, yellow peas, and hulled mung beans had values of 75, 72, and 71, respectively²⁰.
Therefore, based upon the previous description of the DIAAS scoring system, this indicates that if you were to eat an amount of these legumes that only provided the protein RDI for sedentary individuals, and nothing else, you’d likely not get adequate amounts of all the amino acids. This idea may seem a bit abstract, so for the sake of clarity some calculations approximating what this would entail are to follow. Given that this RDI currently equates to approximately 0.8 g/kg body weight, which even for heavier men and women (just to exaggerate, let’s say 70 and 100 kg respectively) would equal 56 and 80 g. That would mean if a woman/man were to consume just ~1112/1578 kcal of chickpeas, 850/1200 kcal mung beans, or ~800/1100 kcal of yellow peas (an amount well under the daily caloric requirements for such individuals, even in extreme circumstances) and absolutely no other sources of protein, they would run into problems (likely more than just those related to amino acid requirements). While the recommended intake per kg of body weight would scale up with an increased frequency of exercise, so would the individual’s total caloric requirements. Furthermore, not only are these foods that possess supposedly lower scores compared to other plant-based protein sources (I.e., soy, seitan made with wheat gluten, lentils, some other legumes, and slightly more processed sources such as powders) but in the absence of dire living conditions and a limited food supply, this is an absurd situation that would almost never occur. Alas, even in such an extreme circumstance, the degree to which these sources would be insufficient is fairly small, and this minor “gap” (for the lack of a better term) can be abolished with the inclusion of just a handful of other foods that supply the limiting essential amino acids.
In conclusion, even prior to escaping the web of mechanistic findings in which many claims pertaining to the different quality of plant and animal sources of protein are woven, it should already be fairly clear as to why the implications many individuals suggest the differences have are far overstated. Though it may have advantages over PDCAAS, DIAAS still has some of its own potential pitfalls and has yet to be adopted as the predominant method for assessing protein digestibility due to the paucity of data on certain foods, the conditions in which many are tested, and the few remaining differences in digestion and amino acid requirements between pigs and humans. Given these points, as well as the fact that many people don’t eat single foods in isolation, and that there is a complete absence of protein deficiency in plant-based populations consuming sufficient calories (many of which also surpass the minimum protein recommendations by a fair amount, as discussed in the Stanford review), these aren’t very relevant outside of the specific abnormal circumstances for which they were created. Henceforth, it is unreasonable for someone who is not limited in the amounts and/or types of foods they can consume to base their dietary choices solely on either of these scoring systems, nor for anyone to use them to suggest certain foods or dietary patterns are inferior with respect to their ability to satisfy nutrient requirements, support normal bodily function, and promote growth.
Significance of Muscle Protein Synthesis and Postprandial Serum Essential Amino Acids
Moving away from supposed digestibility differences and their potential impact on protein quality, a few additional fitness-centric claims worth addressing are those that have blazoned by popular exercise and even nutrition professionals following the release of pro-plant-based films and a recent publication on the topic of plant versus animal-based protein. One such claim is the fact that those consuming a plant-based diet need extra protein compared to omnivores, in addition to the posit plant-based protein powders are inferior even when matched with animal-based sources for leucine content. These statements have been based on results from studies observing differences in the postprandial kinetics of amino acids and/or biomarkers related to muscle protein synthesis between plant and animal sources of protein. The discussion of these claims and the results on which they were based to follow will strongly emphasize the importance of being aware of the aforementioned discordance in mechanistic and outcome-based findings.
The recent study that has been cited by a few individuals in order to suggest that plant-based protein supplements are inferior is focused on blood essential amino acid concentrations following supplementation with powders from various sources²¹. It sought to determine if three different high-quality plant-based protein supplements (with a PDCAAS of 1) with identical leucine content as whey protein isolate, were “bio-equivalent”, which the authors defined as having a similar blood essential amino acid response (EAA). This response was measured primarily by the sum of their concentration in the blood over the course of four hours following consumption of each supplement. It was determined that the three plant-based protein supplements were shown to elicit lower total sums of both total EAA and leucine concentrations in the blood, but the story doesn’t end there. The authors go on to clearly state that two of the blends had leucine Tmax (time to maximum leucine concentration) values similar to whey protein, which they mention is evidence of rapid hyperleucinemia, a response critical to postprandial muscle protein synthesis. Furthermore, they close with the following:
“Based on these data, we can hypothesize that the significant influx of amino acids after soy consumption, results in a greater increase of deamination in the liver and thus, those amino acids are less available in the blood for a shorter time, as compared to milk protein. Therefore, differences in the rate of amino acid appearance in the blood may result from the differential uptake of plant-based protein derived amino acids, which could be a reason why we saw differences in the appearance of blood eAAs in our study when compared to WPI over four hours.”
Thus, not only did two of the plant-based proteins elicit Tmax responses indicative of stimulation of MPS (which in itself is also another ostensible surrogate marker for lean body mass/strength gains), but it’s also known and discussed that the differences in the essential amino acid concentrations could have resulted from differential uptakes of their AAs. Additionally, regardless of whether the differences were explainable, to use this study and conclude that longer elevation of postprandial serum EAA (a supposed proxy for MPS) means anything substantial regarding the nature of subsequent MPS responses, and more importantly the actual measurable outcomes in which improvements are desirable; strength or lean body mass gains, is just conjecture. So, in the end, this study does not provide much evidence suggesting the protein supplements from plant-based sources are significantly less effective than whey protein at all.
Furthermore, it’s been suggested that even acute MPS responses themselves aren’t necessarily strongly associated with muscle hypertrophy following resistance training in all circumstances, especially in novice lifters and immediately following exercise²². This isn’t meant to dismiss the validity of the marker as a whole, as it has clearly proven useful in many circumstances, just to emphasize that other factors play a role and that reliance on a single value without context is problematic. A review by Camera et al. ever so eloquently elaborates upon this issue in discussing the potential disconnect between some acute muscle responses to training and their implications for strength and muscle mass gains below²³.
From the preceding discussion, it is clear that exercise performance is a complex phenomenon resulting from the integration of multiple physiological, biomechanical and psychological factors. As such, it is naive to think that any single ‘molecular marker’ can predict or explain variability in exercise responses and subsequent performance capacity. Indeed, there is often a mismatch between the changes in cellular “mechanistic” variables (often reported as increases in the phosphorylation status of signaling molecules and/or increases in the expression of genes and proteins involved in mitochondrial biogenesis or muscle protein synthesis) and whole body functional outcomes (changes in training capacity or measures of performance).
Finally, even if one was to grant that MPS is the end all be all for ascertaining the effect of dietary protein sources on improvements in muscle size and strength in response to training, multiple recent trials have demonstrated that consumption of mycoprotein, a plant (or rather fungi)-based protein that is derived from the natural fungus Fusarium venenatum and used in popular meat analogs; has resulted in equal or greater resting and post-exercise muscle protein synthesis responses. In the respective trials it was compared either to a leucine matched milk protein supplement or a diet providing the same amount of protein from animal products. The first of these trials published earlier in August observed the responses in muscle protein synthesis following ingestion of milk protein or mycoprotein (in similar amounts and matched for leucine content) both while young, resistance-trained subjects were rested and after they had just trained. Results indicated that the mycoprotein increased mixed muscle fractional synthesis rates to a significantly greater degree than the milk protein during both conditions, while absolute postprandial values trended higher²⁴. The second trial was published earlier in November, and compared the effects of a completely plant-based diet containing mycoprotein as a major protein source to an isonitrogenous (protein matched) and isocaloric high protein omnivorous diet in elderly men, which is especially important to note considering it has been shown the protein needs of elderly increase slightly due to poorer absorption and assimilation of dietary amino acids. After completion of the trial, it was observed that there were no significant differences between the groups with respect to myofibrillar protein synthesis rates taken during rest or after exercise²⁵.
Clearly, the results from these two trials emphasize that there is no necessity for animal products to increase muscle protein synthesis, even in the absence of protein supplementation. As this discussion proceeds onward to outcome-based studies, it will only become even more apparent that not only can plant-based sources of protein support and promote equivalent increases in lean body mass and strength, but they also support and potentially even enhance cardiovascular fitness.
Findings from Outcome-Based Research
Despite all these claims about protein based on mechanisms and the subsequent speculations of their downstream implications, numerous quality observational and controlled studies considering actual outcomes in those following plant-based diets and the relationship to strength/lean body mass show quite the contrary; that plant protein can support muscle growth and maintenance at intakes within the recommended ranges for various demographics.
Since the last section left off with a cursory mention that there is a frequent emphasis on increased protein intake in the elderly to maintain muscle mass and bone density, the first discussed here will be on that demographic. Results from a recent prospective cohort of community-dwelling middle-aged and older adults from China suggested that higher intake of animal or plant-based protein, but not a higher ratio of animal to plant protein, coincided with significant increases in lean body mass (in those with protein intake slightly higher than the RDI, as recommended for older individuals). Consequently, the authors emphasized their findings reinforce that focus should be on achieving protein intakes at or above current recommendations (0.8 g/kg) for older populations to preserve lean body mass, instead of on specific sources²⁶.
Higher dietary intakes of total, animal, and plant protein, regardless of the ratio of animal-to-plant protein, are associated with greater skeletal muscle mass in community-dwelling middle-aged and older Chinese adults with a mean protein intake above the current recommendation for protein of 0.8 g/kg per day.
Protein Requirements for Athletes
That tangent aside, the focus of this discussion will now shift to a few more specific claims and concerns commonly encountered by athletic individuals looking to adopt a plant-based diet. First, it should be noted that while increasing protein intake can certainly help to foster improvements in muscle strength and size, such an effect does not occur ad infinitum. This caveat is reflected in results from the most comprehensive meta-analysis and meta-regression of randomized controlled trials on the effect of protein intake on resistance training-induced gains in muscle mass and strength by Morton et al²⁷. In addition to establishing a breakpoint beyond which no further protein intake elicited gains in lean body mass and strength, the authors also touch on a few other important points in their closing words:
“Given the relatively small effect that protein supplementation has on changes in FFM and 1RM, clearly other variables as a component of RET programmes are of much greater importance…
…Our analysis, and those from others, leads us to conclude that the specifics of protein supplementation (eg, timing, post-exercise protein dose, or protein source) play a minor, if any, role in determining RET-induced gains in FFM and strength over a period of weeks. Instead, our results indicate that a daily protein intake of ~1.6g/kg/day, separated into ~0.25g/ kg doses, is more influential on adaptive changes with RET, at least for younger individuals.”
So according to their findings, one looking to maximize lean body mass and strength gains in response to resistance training should be consuming around 1.6 g/kg body weight (and potentially higher if in a significant caloric deficit, but that is less certain and a separate discussion), ideally spread out in a relatively even manner. Additionally, it is clarified that despite all of the hype suggesting protein intake is of the utmost importance (again, not to say it isn’t), its effect is rather modest, other variables related to training are of greater value, and the timing, post-exercise dose, and source play a very small or non-existent role in the magnitude of the changes observed. With respect to protein sources, while this meta-analysis only included a few trials on soy protein (among whey, beef, and other sources) there are plenty of outcome-based trials on other plant-based proteins demonstrating no significant difference in strength and lean body mass gains in response to resistance training.
Plant vs. Animal Sourced Protein Powders
One of the standout publications on this subject is a meta-analysis of 9 trials comparing equivalent doses of soy protein to various animal-based sources. As illustrated below there were no significant differences in the improvements in strength and lean body mass for the two across a variety of sample populations with different training status, ages, and genders²⁸.
Two later 12-week long trials on groups of young untrained men and women and college-aged men also determined that participants consuming whey or soy protein supplements (matched for leucine content) exhibited no differences in changes of any metric of strength and lean body mass gains in response to resistance training²⁹’³⁰.
Similarly, a smaller 8-week trial involving experienced high-intensity functional training athletes showed no significant difference in the collection of metrics relative to strength and body composition across subjects supplementing equivalent amounts of pea and whey protein³¹.
These results were replicated in a much larger 12-week long randomized controlled trial on 161 untrained males, which displayed that supplementing whey or pea protein alongside upper body resistance training produced notable improvements in lean body mass and strength in comparison to a placebo group, yet no significant differences were observed between the two intervention groups³².
Maximal load (1-RM) during arm curl and muscle torque during the maximum voluntary isometric, concentric and eccentric contractions increased within each group. Statistical analyses only revealed a significant time effect (P < 0.0001). For example, for the Placebo group, the 12-week period produced an increase in the maximal 1-RM strength (+46.1 ± 22.4%), the maximal isometric (+20.5 ± 14.3%), concentric (+15.3 ± 16.2%) and eccentric (+17.2 ± 12.5%) torque. No significant group effect and interaction (group × time) was observed.
Another 8 week trial on trained college-aged males supplementing larger isocaloric doses of rice and whey protein isolates (providing over 3 g of leucine) similarly showcased that there were no significant differences in any improvements for outcomes related to strength and lean body mass in the two groups³³.
However, the doses in this trial were notably larger than previous trials, and may not necessarily be representative of true intakes in the general fitness enthusiast. Fortunately, a recent trial comparing smaller doses (24 grams) of rice and whey protein in combination with 8 weeks of resistance training (with trained men) once again demonstrated that there were no differences in any of the outcomes observed.
Addendum: Finally, confirming the findings of the meta-analysis conducted by Morton et al., a recent controlled trial demonstrated that when consuming protein at a dose of 1.6 g/kg body weight and following a specified resistance training program for 3 weeks, there were no significant difference in any of the measured strength and size outcomes in untrained vegans consuming entirely whole food diets supplemented with soy protein compared to omnivores consuming whole food diets with whey protein. Below are a few of the most relevant figures.
As such, the authors concluded:
A high-protein (~ 1.6 g/kg per day), exclusively plant-based diet (plant-based whole foods + soy protein isolate supplementation) is not different than a protein-matched mixed diet (mixed whole foods + whey protein supplementation) in supporting muscle strength and mass accrual, suggesting that protein source does not affect resistance training-induced adaptations in untrained young men consuming adequate amounts of protein.
Performance of Plant-Based Athletes
Finally, results from the available comparisons of omnivorous and plant-based athletes are in agreement with the trials discussed above, and even suggest plant-based diets may improve measures of endurance exercise capacity.
The most recent publication on this subject compared 56 young, lean, and physically active women who had followed an omnivorous or vegan diet for at least 2 years. Both groups had similar physical activity levels, BMI, body fat percentage, lean body mass, and muscle strength, however, the vegan group had significantly higher estimated VO2 max values and sustained submaximal effort until exhaustion for longer than the omnivores³⁴.
Also worth noting is that the vegan women consumed significantly lower protein and fat intake, but higher carbohydrate and fiber intake.
Another earlier cross-sectional observational study carried out on 67 omnivorous, vegetarian, or vegan recreational runners between 18 and 35 had similar findings. There were 26, 24, and 24 subjects in each group respectively, with at least ⅔ following their current diet for 2 or more years. The main observations were that the three groups had similar training frequency/time and running distance per week. Upon completion of a graded exercise test, no significant differences in maximum power output (relative to body weight and lean body mass) and maximal/submaximal lactate and glucose concentrations were observed³⁵.
Furthermore, analysis of nutrient intakes demonstrated that vegans and vegetarians had a similar or greater intake of virtually all micronutrients, with the exceptions of calcium and B12, with the latter being far enough below reference daily intake for concern, only emphasizing the known importance of supplementing B12.
Lastly, it’s at least worth mentioning there is a 2016 review that set out to determine if there were any notable differences in the physical performance of vegetarians compared to omnivores. The authors’ search yielded 8 studies, 3 on muscular power and strength, three on anaerobic and aerobic performance, and one on immune function.
The 3 on muscular power were all on elderly men and showed no significant differences in muscular strength or power outcomes except one (Wells et al. 2003) where the LOV group increased knee extension strength significantly. One of the remaining trials (Campbell et al. 1999) showed that the omnivorous group had greater changes in whole-body composition and type II muscle fiber size, however they clearly maintained a higher protein intake during the intervention, which is a major confounder, especially in the elderly.
The four studies observing the effect of vegetarian diets on aerobic/anaerobic performance had similar results, all demonstrating no significant difference in any measures of endurance, speed, or perceived effort. The final study on immune function also showed no differences in any of the parameters tested following aerobic exercise³⁶.
Therefore, the authors concluded that there seemed to be no indication that a vegetarian diet hindered or improved athletic performance, but emphasized that due to numerous limitations of these older studies that there is a need for longer, larger, and more rigorous trials on the subject.
Before closing out, one minor addendum to the prior content; as discussed in passing earlier on, many of the claims and concerns regarding an inferiority of plant-based protein sources hinge on the fact they contain lower amounts of the essential amino acids (especially leucine) that are intrinsic to the relationship between protein intake and increased muscle/strength gains. While this may be true to an extent, it’s fairly overexaggerated. If one were taking in the recommended 1.6 g/kg of protein per day as deemed to be the breaking point by Morton et al., they should have absolutely no issue with these EAAs, and could also easily achieve the 2.5–3 g leucine commonly referred to as the minimum amount in a mixed meal required to initiate a muscle protein synthesis response. While claims of the difficulty in achieving sufficient anabolic amino acid intake on a plant-based diet are widespread, the reality is that with adequate calories and total protein it’s almost difficult to not get the desired amounts, be it on a daily or per meal basis, and whether the source is animal or plant-based. This holds especially true if one is including protein supplements as a large proportion of all athletes already do given their convenience.
As indicated numerous times, outside of the context of severe malnutrition or disease, the consumption of plant-based sources of protein within current daily recommendations (according to activity status) is more than adequate to support increases in strength and muscle mass, and can be equivalent to animal-based protein. Furthermore, it should be acknowledged that the focus on protein intake seen in the media and advocated by bodybuilders, powerlifters, athletes, and even the average person is over-exaggerated. Although calculated increases can clearly confer a benefit (potentially a bit more in those who are experienced with resistance training), said benefit is finite, and the magnitude of the effect on mass and strength gains relative to other factors, such as the nature of the training itself, sleep, hydration, a caloric surplus, and other components aiding in recovery, is somewhat limited. In some cases, this constant concern with consuming large (and in a few instances quite frankly obscene) amounts of protein can be a distraction from other important considerations for achieving success in various exercise endeavors. For those looking to push the boundaries of what is physically achievable, elicit weight loss, and maintain strength during a caloric deficit; it can certainly be a relevant modifiable factor that deserves more attention and is an important consideration, but for many individuals, it appears to be given all too much.
In closing, hopefully this write-up has been helpful in answering some of the more common questions and concerns pertaining to protein in a plant-based diet, both for the average person, active individuals, and athletes. Equally, it should serve to underscore the importance of not taking strong stances on the effect(s) of certain interventions and lifestyle habits based on findings from animal models or mechanistic studies (whether they are pertinent to nutrition, medicine, fitness, or other similar disciplines) without confirmation through good quality outcome-based studies.
1. Le, L. T., & Sabaté, J. (2014). Beyond meatless, the health effects of vegan diets: findings from the Adventist cohorts. Nutrients, 6(6), 2131–2147. https://doi.org/10.3390/nu6062131
2. Appleby, P. N., Crowe, F. L., Bradbury, K. E., Travis, R. C., & Key, T. J. (2016). Mortality in vegetarians and comparable nonvegetarians in the United Kingdom. The American journal of clinical nutrition, 103(1), 218–230. https://doi.org/10.3945/ajcn.115.119461
3. Satija, A., Bhupathiraju, S. N., Spiegelman, D., Chiuve, S. E., Manson, J. E., Willett, W., Rexrode, K. M., Rimm, E. B., & Hu, F. B. (2017). Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults. Journal of the American College of Cardiology, 70(4), 411–422. https://doi.org/10.1016/j.jacc.2017.05.047
4. Satija, A., Bhupathiraju, S. N., Rimm, E. B., Spiegelman, D., Chiuve, S. E., Borgi, L., Willett, W. C., Manson, J. E., Sun, Q., & Hu, F. B. (2016). Plant-Based Dietary Patterns and Incidence of Type 2 Diabetes in US Men and Women: Results from Three Prospective Cohort Studies. PLoS medicine, 13(6), e1002039. https://doi.org/10.1371/journal.pmed.1002039
5. Kim, H., Caulfield, L. E., Garcia‐Larsen, V., Steffen, L. M., Coresh, J., & Rebholz, C. M. (2019). Plant‐Based Diets Are Associated With a Lower Risk of Incident Cardiovascular Disease, Cardiovascular Disease Mortality, and All‐Cause Mortality in a General Population of Middle‐Aged Adults. Journal of the American Heart Association, 8(16), 1–13. https://doi.org/10.1161/jaha.119.012865
6. Melina, V., Craig, W., & Levin, S. (2016). Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. Journal of the Academy of Nutrition and Dietetics, 116(12), 1970–1980. https://doi.org/10.1016/j.jand.2016.09.025
7. Schwingshackl, L., Schwedhelm, C., Hoffmann, G., Lampousi, A.-M., Knüppel, S., Iqbal, K., Bechthold, A., Schlesinger, S., & Boeing, H. (2017b). Food groups and risk of all-cause mortality: a systematic review and meta-analysis of prospective studies. The American Journal of Clinical Nutrition, 105(6), 1462–1473. https://doi.org/10.3945/ajcn.117.153148
8. Bechthold, A., Boeing, H., Schwedhelm, C., Hoffmann, G., Knüppel, S., Iqbal, K., De Henauw, S., Michels, N., Devleesschauwer, B., Schlesinger, S., & Schwingshackl, L. (2017b). Food groups and risk of coronary heart disease, stroke and heart failure: A systematic review and dose-response meta-analysis of prospective studies. Critical Reviews in Food Science and Nutrition, 59(7), 1071–1090. https://doi.org/10.1080/10408398.2017.1392288
9. Schwingshackl, L., Hoffmann, G., Lampousi, A. M., Knüppel, S., Iqbal, K., Schwedhelm, C., Bechthold, A., Schlesinger, S., & Boeing, H. (2017). Food groups and risk of type 2 diabetes mellitus: a systematic review and meta-analysis of prospective studies. European journal of epidemiology, 32(5), 363–375. https://doi.org/10.1007/s10654-017-0246-y
10. Schwingshackl, L., Schwedhelm, C., Hoffmann, G., Knüppel, S., Iqbal, K., Andriolo, V., Bechthold, A., Schlesinger, S., & Boeing, H. (2017). Food Groups and Risk of Hypertension: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies. Advances in nutrition (Bethesda, Md.), 8(6), 793–803. https://doi.org/10.3945/an.117.017178
11. Schlesinger, S., Neuenschwander, M., Schwedhelm, C., Hoffmann, G., Bechthold, A., Boeing, H., & Schwingshackl, L. (2019). Food Groups and Risk of Overweight, Obesity, and Weight Gain: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies. Advances in nutrition (Bethesda, Md.), 10(2), 205–218. https://doi.org/10.1093/advances/nmy092
12. Schwingshackl, L., Schwedhelm, C., Hoffmann, G., Knüppel, S., Laure Preterre, A., Iqbal, K., Bechthold, A., De Henauw, S., Michels, N., Devleesschauwer, B., Boeing, H., & Schlesinger, S. (2017). Food groups and risk of colorectal cancer. International Journal of Cancer, 142(9), 1748–1758. https://doi.org/10.1002/ijc.31198
13. Kazemi, A., Barati-Boldaji, R., Soltani, S., Mohammadipoor, N., Esmaeilinezhad, Z., Clark, C. C. T., Babajafari, S., & Akbarzadeh, M. (2020). Intake of Various Food Groups and Risk of Breast Cancer: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies. Advances in Nutrition, 1–41. https://doi.org/10.1093/advances/nmaa147
14. Schwingshackl, L., Hoffmann, G., Iqbal, K., Schwedhelm, C., & Boeing, H. (2018). Food groups and intermediate disease markers: a systematic review and network meta-analysis of randomized trials. The American Journal of Clinical Nutrition, 108(3), 576–586. https://doi.org/10.1093/ajcn/nqy151
15. Mariotti, F., & Gardner, C. D. (2019). Dietary Protein and Amino Acids in Vegetarian Diets-A Review. Nutrients, 11(11), 2661. https://doi.org/10.3390/nu11112661
16. Mariotti, F. (2017). Plant Protein, Animal Protein, and Protein Quality. Vegetarian and Plant-Based Diets in Health and Disease Prevention, 621–642. https://doi.org/10.1016/b978-0-12-803968-7.00035-6
17. Wong, C. H., Siah, K. W., & Lo, A. W. (2018). Estimation of clinical trial success rates and related parameters. Biostatistics, 20(2), 273–286. https://doi.org/10.1093/biostatistics/kxx069
18. Bailey, H. M., & Stein, H. H. (2019). Can the digestible indispensable amino acid score methodology decrease protein malnutrition. Animal Frontiers, 9(4), 18–23. https://doi.org/10.1093/af/vfz038
19. Tomé, D. (2013). Digestibility Issues of Vegetable versus Animal Proteins: Protein and Amino Acid Requirements — Functional Aspects. Food and Nutrition Bulletin, 34(2), 272–274. https://doi.org/10.1177/156482651303400225
20. Kashyap, S., Varkey, A., Shivakumar, N., Devi, S., Reddy B H, R., Thomas, T., Preston, T., Sreeman, S., & Kurpad, A. V. (2019). True ileal digestibility of legumes determined by dual-isotope tracer method in Indian adults. The American journal of clinical nutrition, 110(4), 873–882. https://doi.org/10.1093/ajcn/nqz159
21. Brennan, J. L., Keerati-U-Rai, M., Yin, H., Daoust, J., Nonnotte, E., Quinquis, L., St-Denis, T., & Bolster, D. R. (2019). Differential Responses of Blood Essential Amino Acid Levels Following Ingestion of High-Quality Plant-Based Protein Blends Compared to Whey Protein-A Double-Blind Randomized, Cross-Over, Clinical Trial. Nutrients, 11(12), 2987. https://doi.org/10.3390/nu11122987
22. Mitchell, C. J., Churchward-Venne, T. A., Parise, G., Bellamy, L., Baker, S. K., Smith, K., Atherton, P. J., & Phillips, S. M. (2014). Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men. PloS one, 9(2), e89431. https://doi.org/10.1371/journal.pone.0089431
23. Camera, D. M., Smiles, W. J., & Hawley, J. A. (2016). Exercise-induced skeletal muscle signaling pathways and human athletic performance. Free Radical Biology and Medicine, 98, 131–143. https://doi.org/10.1016/j.freeradbiomed.2016.02.007
24. Monteyne, A. J., Coelho, M. O. C., Porter, C., Abdelrahman, D. R., Jameson, T. S. O., Jackman, S. R., Blackwell, J. R., Finnigan, T. J. A., Stephens, F. B., Dirks, M. L., & Wall, B. T. (2020). Mycoprotein ingestion stimulates protein synthesis rates to a greater extent than milk protein in rested and exercised skeletal muscle of healthy young men: a randomized controlled trial. The American Journal of Clinical Nutrition, 112(2), 318–333. https://doi.org/10.1093/ajcn/nqaa092
25. Monteyne, A. J., Dunlop, M. V., Machin, D. J., Coelho, M. O. C., Pavis, G. F., Porter, C., Murton, A. J., Abdelrahman, D. R., Dirks, M. L., Stephens, F. B., & Wall, B. T. (2020). A mycoprotein based high-protein vegan diet supports equivalent daily myofibrillar protein synthesis rates compared with an isonitrogenous omnivorous diet in older adults: a randomized controlled trial. British Journal of Nutrition, 1–35. https://doi.org/10.1017/s0007114520004481
26. Li, C.-, Fang, A.-, Ma, W.-, Wu, S.-, Li, C.-, Chen, Y.-, & Zhu, H.-. (2019). Amount Rather than Animal vs Plant Protein Intake Is Associated with Skeletal Muscle Mass in Community-Dwelling Middle-Aged and Older Chinese Adults: Results from the Guangzhou Nutrition and Health Study. Journal of the Academy of Nutrition and Dietetics, 119(9), 1501–1510. https://doi.org/10.1016/j.jand.2019.03.010
27. 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., & Phillips, S. M. (2017). 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), 376–384. https://doi.org/10.1136/bjsports-2017-097608
28. Messina, M., Lynch, H., Dickinson, J. M., & Reed, K. E. (2018). No Difference Between the Effects of Supplementing With Soy Protein Versus Animal Protein on Gains in Muscle Mass and Strength in Response to Resistance Exercise. International Journal of Sport Nutrition and Exercise Metabolism, 28(6), 674–685. https://doi.org/10.1123/ijsnem.2018-0071
29. Mobley, C. B., Haun, C. T., Roberson, P. A., Mumford, P. W., Romero, M. A., Kephart, W. C., Anderson, R. G., Vann, C. G., Osburn, S. C., Pledge, C. D., Martin, J. S., Young, K. C., Goodlett, M. D., Pascoe, D. D., Lockwood, C. M., & Roberts, M. D. (2017). Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-Aged Males. Nutrients, 9(9), 972. https://doi.org/10.3390/nu9090972
30. Lynch, H. M., Buman, M. P., Dickinson, J. M., Ransdell, L. B., Johnston, C. S., & Wharton, C. M. (2020). No Significant Differences in Muscle Growth and Strength Development When Consuming Soy and Whey Protein Supplements Matched for Leucine Following a 12 Week Resistance Training Program in Men and Women: A Randomized Trial. International journal of environmental research and public health, 17(11), 3871. https://doi.org/10.3390/ijerph17113871
31. Banaszek, A., Townsend, J. R., Bender, D., Vantrease, W. C., Marshall, A. C., & Johnson, K. D. (2019). The Effects of Whey vs. Pea Protein on Physical Adaptations Following 8-Weeks of High-Intensity Functional Training (HIFT): A Pilot Study. Sports (Basel, Switzerland), 7(1), 12. https://doi.org/10.3390/sports7010012
32. Babault, N., Païzis, C., Deley, G., Guérin-Deremaux, L., Saniez, M. H., Lefranc-Millot, C., & Allaert, F. A. (2015). Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, Placebo-controlled clinical trial vs. Whey protein. Journal of the International Society of Sports Nutrition, 12(1), 3. https://doi.org/10.1186/s12970-014-0064-5
33. Joy, J. M., Lowery, R. P., Wilson, J. M., Purpura, M., De Souza, E. O., Wilson, S. M., Kalman, D. S., Dudeck, J. E., & Jäger, R. (2013). The effects of 8 weeks of whey or rice protein supplementation on body composition and exercise performance. Nutrition journal, 12, 86. https://doi.org/10.1186/1475-2891-12-86
34. Boutros, G. H., Landry-Duval, M.-A., Garzon, M., & Karelis, A. D. (2020). Is a vegan diet detrimental to endurance and muscle strength? European Journal of Clinical Nutrition, 74(11), 1550–1555. https://doi.org/10.1038/s41430-020-0639-y
35. Nebl, J., Haufe, S., Eigendorf, J., Wasserfurth, P., Tegtbur, U., & Hahn, A. (2019). Exercise capacity of vegan, lacto-ovo-vegetarian and omnivorous recreational runners. Journal of the International Society of Sports Nutrition, 16(1), 1–8. https://doi.org/10.1186/s12970-019-0289-4
36. Craddock, J. C., Probst, Y. C., & Peoples, G. E. (2016). Vegetarian and Omnivorous Nutrition — Comparing Physical Performance. International Journal of Sport Nutrition and Exercise Metabolism, 26(3), 212–220. https://doi.org/10.1123/ijsnem.2015-0231