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Study Breakdown: SWAP-MEAT Athlete Study

Updated: Jul 23, 2023

Athletes are often afraid that their performance will suffer when eating plant-based. Is this the case? Here, we dissect a new paper published in the Nutrition Journal that asked this question.


Plant-based diets are diets that contain mostly plant foods, such as fruits, vegetables, whole grains, legumes (e.g., beans/lentils), and nuts and seeds. Different variations of such diets include vegan and vegetarian diets, which are associated with a reduced risk of certain chronic diseases (1,2), and are more environmentally sustainable as they generally require less land and water, and produce less greenhouse gas emissions than omnivorous diets (3).


For athletes who may be interested in adopting a more plant-based diet, one important question lingers: will my performance suffer. In this article, we will take you through a trial published just two weeks ago by Roberts and colleagues that attempted to answer this question: the *SWAP-MEAT Athlete study (4).


Research Questions

This study was designed to attempt to answer the following two questions:

  1. How does a healthy, near-vegan diet compare to an omnivorous diet for performance?

  2. How does a meat-alternative-rich diet compare to an omnivorous diet for performance?


Study Design

This study was a randomised crossover trial, where each participant ate each diet for a four-week period, then switched over to eat the next diet for a four-week period, then switched to eat the final diet for another four weeks. The order of which was randomised for each participant. All the while, participants kept a constant physical activity regimen of running or lifting ~3–4 times per week—to ensure that diet was the only thing that was different among these three four-week periods.


Dietary Interventions

The healthy near-vegan diet was termed a "whole-food plant-based diet", and study participants consumed at least two meals per day consisting of fruits, vegetables, whole grains, legumes, and nuts and seeds. The athletes got most of their protein from protein-rich plant foods like tofu, tempeh, black beans, and quinoa.


For the meat-replacement-rich diet, study participants were told to consume at least two servings of meat alternative protein sources (e.g., Beyond Meat) per day and no consumption of animal meat was allowed (except for fish once per week).


For the omnivorous diet, study participants were told to consume at least two servings of animal meat per day in the form of red meat or poultry. Fish consumption was permitted once per week.


All study participants were given 100 dollars per four-week diet phase to purchase the necessary foods.


Study Participants

The study population was made up of 22 healthy young (~26-years old) male and female recreational athletes—half of which were runners; half of which were resistance trainers. Participants reported training for just under 4 hours per week (on average), and had a training history of 6 years (on average).


Measures of Performance

Endurance

Endurance performance was measured as performance in the Cooper 12-minute run—an all-out 12-minute effort on a 400 m running track. A secondary outcome was VO₂max (mL O₂/kg/min), estimated by Garmin watch (Forerunner 235).


Strength

Strength performance was measured over two days (separated by 48 hours):

  • Day 1: Participants completed the maximum number of push-ups and pull-ups that they could do

  • Day 2: Participants completed 3-rep maximum tests for machine-based exercises (chest press, leg press, lat pulldown), with a 10–15-minute rest between sets.

    • These measures of strength were combined into an overall machine-based strength score


Results

Table 1 presents the results for all endurance and strength measures of performance.


Endurance Performance

On average, the whole-food plant-based diet group ran 23 metres less than the omnivorous group, whereas the meat-alternative-rich diet group ran 3 metres less (on average) than the omnivorous diet group. These results were not statistically significantly different from each other (see the Technical Terms at the end of the article for an explanation of statistical significance), and the confidence intervals showed compatibility between an improvement or impairment in performance for the plant-based diet phases compared to the omnivorous diet phases.


Differences in VO₂max were likewise non-significantly different across diet phases, however both plant-based diet phases showed slight increases compared to the omnivorous diet phase.


Table 1. Results for Endurance and Strength Performance During Each Diet Phase


Strength Performance

Once again, differences in machine-based strength performance were non-significant. The plant-based diets showed slightly lower values for all strength measures (on average), but because the results were not statistically significant, we can’t determine whether these are “real” differences or if they arose by chance. In addition, like the endurance performance results, some individuals improved strength measures on the plant-based diets compared to the omnivorous diets, and vice versa (see: Supplementary Figures 2 and 4 in the paper).


Interesting Findings

There are three key findings that may reflect some nuances to keep in mind when interpreting the study:

  1. When consuming both plant-based diets, study participants ate significantly less protein than when eating an omnivorous diet (Figure 1)

  2. Study participants lost body weight and fat when on the plant-based diets

  3. One individual had massive reductions in strength performance during the plant-based diet phases compared to the omnivorous diet phase (see: Supplementary Figures 2 and 4 in the paper)


Figure 1. Protein Intakes During each Diet Phase


Why are these points important? They may partly explain the slight differences in performance (particularly strength) outcomes between diet phases.


Consuming enough protein is important for performance (see our article on protein), and perhaps the substantially lower intakes during the plant-based diet phases influenced the slightly improved performance observed during the omnivorous diet phase (although differences were not statistically significantly different). In fact, the athletes didn’t even meet the lower level of protein intake recommended for athletes by the Academy of Nutrition and Dietetics, Dietitians of Canada, and Academy of Sports Medicine (1.2 g/kg/d) during the whole-food plant-based diet phase (5), or the lower level recommendation from the International Society for Sports Nutrition (1.4 g/kg/d) during either plant-based diet phase (6), which is not ideal for performance.


In addition, losing body weight and fat during the plant-based diet phases indicates that the individuals were in a caloric deficit (even though they reported eating similar amounts of calories), which may have influenced the non-significant (small) differences in performance outcomes.


Further, the single individual who performed remarkably worse for strength outcomes during the plant-based diet phases slightly skewed the results. Indeed, the researchers performed a sensitivity analysis with this individual removed and found a slight reduction in the estimates of differences in strength outcomes between diet phases.


Summary

To bring things together, this study provides evidence that athletes can perform similarly on plant-based diets, even when not consuming recommended levels of protein, and with the caveat that this was a relatively short trial. In addition, had the athletes been eating similar amounts of protein and calories during all phases, we likely wouldn't see any difference in performance—non-significant or otherwise. This is good news for those who want to improve their diet quality by incorporating more high-quality plant foods (e.g., fruits, vegetables, whole grains, legumes, nuts and seeds), and these changes also provide a means to lower your environmental impact.


We hope you enjoyed this study breakdown. Tell us what you thought via DM on Instagram! If you want a critical breakdown of your football skills, contact us at [email protected] to book in for a session.


Check back in with us next week for more!


Patrick Elliott, BSc, MPH

Health and Nutrition Science Communication Officer at Training121

Founder of Just Health — IG: @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.


*SWAP-MEAT stands for: Study With Appetizing Plant-food, Meat Eating Alternatives Trial


References

(1) Dinu M, Abbate R, Gensini GF, Casini A, Sofi F. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Crit Rev Food Sci Nutr. 2017;57(17):3640-9. Available at: https://pubmed.ncbi.nlm.nih.gov/26853923/


(2) Key TJ, Fraser GE, Thorogood M, et al. Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr. 1999;70(3 Suppl):516S-524S. Available at: https://pubmed.ncbi.nlm.nih.gov/10479225/


(3) Willett W, Rockström J, Loken B, et al. Food in the Anthropocene: the EAT-Lancet Commission on healthy diets from sustainable food systems. Lancet. 2019;393(10170):447-92. Available at: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31788-4/fulltext


(4) Roberts AK, Busque V, Robinson JL, Landry MJ, Gardner CD. SWAP-MEAT Athlete (study with appetizing plant-food, meat eating alternatives trial) - investigating the impact of three different diets on recreational athletic performance: a randomized crossover trial. Nutr J. 2022;21(1):69. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9666956/


(5) Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501-28. Available at: https://journals.lww.com/acsm-msse/Fulltext/2016/03000/Nutrition_and_Athletic_Performance.25.aspx


(6) Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, Purpura M, Ziegenfuss TN, Ferrando AA, Arent SM, Smith-Ryan AE, Stout JR, Arciero PJ, Ormsbee MJ, Taylor LW, Wilborn CD, Kalman DS, Kreider RB, Willoughby DS, Hoffman JR, Krzykowski JL, Antonio J. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017 Jun 20;14:20. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5477153/


Technical Terms

Randomised crossover trial: This is similar to a parallel randomised controlled trial, which is where individuals are randomised into two or more groups and followed for a set time period, upon the end of which they are compared for the outcome of interest. In a crossover trial, however, each person acts as their own comparison. In this trial, the results for each participant while eating a particular diet were compared to their results while eating the other diets. This study design offers greater internal validity than a parallel trial, meaning that we can say with slightly more certainty that the results are likely to be true effects.


VO₂max: This is the maximum rate of oxygen consumption attainable during physical exertion, and is measured as millilitre of oxygen consumed per kg of body weight per minute (mL O₂/kg/min). Athletes (particularly endurance athletes) have a greater VO₂max compared to untrained individuals.


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%, and thus not likely to be due to chance.


Confidence interval: This is a statistical term that describes a range of values (usually a 95% confidence interval) that may include the true population value that we are trying to estimate. In other words, if we did this exact study 20 times, we would expect the true effect of the meat-alternative-rich diet eaten in this study on metres covered in a 12-minute all-out run to be contained within the confidence interval 19 out of 20 (95% of) times. The confidence interval also gives a measure of the precision of an estimate—if it was between -20 metres and +20 metres, we would say it is a more precise estimate, for example. Because this trial only included 22 individuals, the confidence interval will never be as precise as it would be with much larger samples.


Calorie deficit: This is a state of energy intake that is lower than what is required for your body to maintain body weight, and thus leads to a decrease in body weight, the majority of which being body fat (but muscle will be lost to some extent, too).


Sensitivity analysis: This is an analysis that is slightly different from the main analysis of a paper, and is done to explore how a specific factor may influence (or have influenced) results, and/or to see how robust a study finding is to additional (relevant) model assumptions. In this study, a sensitivity analysis was conducted excluding an outlier in the resistance-trained group, to see how much their results influenced overall (average) results.

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