Updated: Jul 23
New research has questioned the common claim that animal sources of protein are superior to plant sources for muscle and strength gains. Read on to learn the specifics.
There is a longstanding belief in the sports nutrition world, and in wider society, that animal sources of protein are inherently superior for building muscle size and strength compared to plant sources. There are good reasons for this. First of all, animal sources of protein like meat, dairy, and eggs often contain more essential amino acids (EAAs) than plant sources, which help to fire up the muscle building process. These EAAs are also building blocks of muscle protein, and we must eat them if we want to gain muscle size. Secondly, animal sources of protein tend to be more digestible (or bioavailable) than plant sources, meaning that more of the protein is absorbed and therefore used by the body.
With this knowledge, it doesn’t seem to be a stretch to think that eating animal sources of protein would lead to greater gains in the gym. However, a randomised controlled trial (RCT) from 2021 found that after 12 weeks of eating a high-protein diet and engaging in equivalent resistance training programmes, both vegans and omnivores gained similar amounts of muscle strength and size (Figure 1) (1). Similarly, we recently covered another trial that found no significant differences between plant-based and omnivorous diet interventions for strength performance. While these were well-conducted studies, we would ideally like to see the results repeated to improve our confidence in them. A new study published in The Journal of Nutrition has done just that (2), so let’s dig into it.
This study recruited 22 healthy, young adults who had some experience in resistance training for a 10-week trial. The participants were randomly allocated to either the intervention group—which was a high-protein vegan diet with about one-third of daily protein coming from Quorn products (mycoprotein)—or the control group—which consisted of a high-protein omnivorous diet with about 30% of daily protein coming from a milk protein supplement. Both groups were prescribed an intense 10-week lifting programme consisting of 5 exercise sessions per week aimed at maximising muscle gains (in a “pull-push-lower” pattern).
After 10 weeks, there were no significant differences in muscle gains between groups. The vegan group gained 3.1 kg of lean mass on average; the omnivorous group gained 2.6 kg of lean mass on average (Figure 2). Similar improvements in quads, hamstring, and adductor (inner thigh) muscle size were also reported for both groups.
Figure 2. Changes in lean mass at week 2 (left), week 5 (centre), and post-intervention (right) between omnivores (white dots) and vegans (black dots) (2). Each dot represents each participant in the study and the horizontal line represents the average result for each group of participants. Results: both groups improved lean mass on average throughout the study (indicated by being above the dotted line of zero change).
For muscle strength, both groups improved their squat and force production during knee extension to a similar degree, however the vegan group improved their incline bench press significantly more so than the omnivorous group, with their deadlift improving to a similarly greater degree (Figure 3).
Figure 3. Changes in % deadlift strength (left), % squat strength (centre-left), % incline bench press strength (centre-right), and % knee extensor peak isometric torque (right) between omnivores (white dots) and vegans (black dots) from baseline to post-intervention (2). Each dot represents each participant in the study and each horizontal line represents the average result for all participants. Results: both groups improved each measure on average throughout the study, however vegans had significant improvements in incline bench press compared to omnivores (shown by ✝).
How can this be? Previous research has shown that once you eat about 1.6 grams of protein per kilogram of body weight per day (g/kg/d), eating more protein likely has no additional effect on gains (3,4). However, these analyses were using data on people eating meat, dairy, and eggs, so whether this was also true for vegans was not fully understood.
In this study, both the omnivores and the vegans ate more than 2.0 g/kg/d of protein and in the 2021 study mentioned earlier, participants consumed about 1.6 g/kg/d of protein (1). What this suggests is that once you eat the recommended amounts of protein for strength athletes (≥ 1.6 g/kg/d), the source (animal/plant) is not important.
The landscape in the sports nutrition world is changing with respect to protein and performance. Indeed, experts in the field now acknowledge that once you eat enough protein, whether it comes from plant or animal foods doesn’t seem to impact muscle or strength gains (in young adults at least). This is welcome news for those who want to eat more plant sources of protein (e.g., tofu, plant-based meats, lentils, soy milk, etc.) for either ethical, environmental, or health reasons.
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That’s all for this week, I hope you took something from it. Check back next week for another breakdown of new research!
Patrick Elliott, BSc, MPH
Health and Nutrition Science Communication Officer at Training121
Founder of Just Health — Instagram: @just.health.info
Health Disclaimer: this article is for informational and educational purposes only, and is not a substitute for professional advice. For health advice, speak to a physician or other qualified health-care professional, and for nutrition advice, speak to a qualified nutrition professional (e.g., registered dietitian). The use of information on this site is solely at your own risk.
(1) Hevia-Larraín V, Gualano B, Longobardi I, et al. High-Protein Plant-Based Diet Versus a Protein-Matched Omnivorous Diet to Support Resistance Training Adaptations: A Comparison Between Habitual Vegans and Omnivores. Sports Med. 2021;51(6):1317-30. Available at: https://pubmed.ncbi.nlm.nih.gov/33599941/
(2) Monteyne AJ, Coelho MO, Murton AJ, et al. VEGAN AND OMNIVOROUS HIGH PROTEIN DIETS SUPPORT COMPARABLE DAILY MYOFIBRILLAR PROTEIN SYNTHESIS RATES AND SKELETAL MUSCLE HYPERTROPHY IN YOUNG ADULTS [published online ahead of print, 2023 Feb 21]. J Nutr. 2023;S0022-3166(23)12680-0. Available at: https://www.sciencedirect.com/science/article/pii/S0022316623126800
(3) Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM. 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. Br J Sports Med. 2018 Mar;52(6):376-84. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5867436/
(4) Nunes EA, Colenso-Semple L, McKellar SR, et al. Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults. J Cachexia Sarcopenia Muscle. 2022;13(2):795-810. Available at: https://onlinelibrary.wiley.com/doi/epdf/10.1002/jcsm.12922
Essential amino acids (EAAs): These are the amino acids that we need to get from our diet to function. There are 20 amino acids in total, nine of which are EAAs (phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, histidine). The most important for triggering the process of muscle build up (muscle protein synthesis) is called leucine.
Bioavailable: This refers to how much of a nutrient our body can absorb, so a bioavailable nutrient means a well-absorbed nutrient.
Randomised controlled trials: Also known as RCTs, these are a type of intervention study where a group of recruited individuals are randomly assigned to groups within a study. The rationale for randomisation is to reduce bias, that is, to evenly distribute among groups any factors that may influence (or bias) the result of interest. For example, if we have a group of 100 people who will either be given a multivitamin or placebo and followed for 10 years to see how many in each group dies, we would randomise so that each group is on average similar for factors like age, physical activity status, smoking status, and so on. If we didn't randomise, there's a greater chance that one group may end up being different enough from another group such that the results of the study may be biased, e.g., one group could have a lot more smokers or sedentary individuals, which would likely influence the outcome of interest (death).
Statistical significance: This is a term to describe the likelihood of whether a finding in a study is a “real” finding, or if it is the result of chance. Statistical significance is denoted by a p-value, which is usually set at a significance (alpha) level of 0.05. This means that if a result is significant at this level (p < 0.05), we can say that the probability of getting a value as or more extreme than the observed value (under the assumption that the null hypothesis is true) is less than 5%.
Lean mass: This refers to more than just muscle mass, also including bone, connective tissue, organs, and water. In a trial like this, changes in lean mass are likely driven mostly by changes in muscle mass.