Plant-based or omnivorous diet for muscle gain

Is diet preference and overall protein intake superior to source of protein?

Introduction

If you want to optimally gain muscle, lift weights and make sure your protein intake is on the higher side [1]. There is little debate that this is the magic formula for getting ‘jacked’. For years, however, there has been a prevailing notion that proteins derived from animal sources (e.g. meat, poultry, dairy, etc.) are superior for muscle gain/maintenance than those derived from plant-based sources such as soy or pea [2]. This is unwelcome news for those who want to build a respectable physique or get stronger but would still like to consume a plant-based diet (for whatever reason). Are the two in conflict with one another? Or are you relegated to inferior ‘gainz’ should you opt for a plant-based way of eating?

Mechanistic insights   

From a mechanistic standpoint, acute feeding studies—i.e. studies that provide various protein sources in isolation to individuals and subsequently measure rates of muscle protein synthesis in skeletal muscle (MPS) over the following hours—show that whey protein (or dairy) typically stimulate MPS to a greater degree than plant-based sources such as soy protein [3-6]. (Score one for animal proteins!) This outcome is thought to be a consequence of the amino acid profile and/or digestibility between plant and animal sources with animal proteins having a more advantageous anabolic profile/digestibility score than plant proteins [2]. Thus, it would appear that animal protein sources are the way to go to optimize muscle and strength gains alongside resistance exercise training. While, mechanistically, this all makes sense, extrapolating the acute data over longer-term studies have been…less clear.  

Longer-term insights

Indeed, when researchers look at longer-term training studies and protein intakes and measure actual muscle gain (not just acute changes in protein synthesis rates), it is often shown that as long as total protein intake and amino acid profile is sufficient (key word), it does not matter if you supplement the diet with whey or soy or what have you [7]. (Score 1 for plant proteins!) This at least shows that there can be a place for supplemental plant-based proteins and muscle/strength gains.

Predictably, however, this leads to the inevitable counterargument that the subjects in these studies built their bodies initially on animal protein sources (indeed, none were conducted with habitual vegans or vegetarians); so while the subjects in these studies may be doing well in spite of the plant-based protein sources, animal sources are likely superior when beginning training or during longer training periods.

This reminds me of the case of Kendrick Farris, a U.S. Olympic Weightlifter popularly known for following a vegan diet leading up to his 2016 Rio appearance. While certainly impressive, Kendrick also competed in the Olympics in 2008 and 2012 following an omnivorous diet in both occasions. Thus, the jury is out whether he performs well because or in spite of his recent dietary change. (Regardless, the guy is obviously a beast!)  

Back to longer-term trials for a second: often times protein intakes are not controlled in such studies or subjects are told to abstain from meat but can still consume foods such as eggs and milk which are obviously animal-based and confound the validity of such study results and their applications in bona fide plant-based/vegan populations. Thus, we really don’t know the true extent to which a completely plant-based diet stacks up to an omnivorous diet for strength and muscle gains.

Which brings me to todays’ study. Until recently, no trial has never actually put habitual vegans and omnivores head-to-head on a weightlifting program with sufficient protein and assessed gains in muscle mass and strength. In doing so, we finally have an (initial) answer as to whether or not a plant-based diet with exclusively plant-based proteins can achieve similar muscle and strength outcomes compared to an omnivorous diet with animal proteins. What did the investigators find?

High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: a comparison between habitual vegans and omnivores

Victoria Hevia-Larraín et al. 2021 Sports Medicine

Methods

In this recently published study, the researchers took young, healthy habitual vegans and omnivores and supplemented them with either soy or whey protein up to a total daily protein intake of 1.6 g/kg alongside a 12-week, progressive, lower-body resistance-training program (two training days per week under research team supervision).

Groups were not randomized (given the nature of the research question) but were matched for age, body composition, strength, and a whole host of blood measures (save vitamin D). At baseline, omnivores did consume more total protein before the intervention (not a big shocker), but similar overall energy intake compared to vegans.

Muscle mass (whole body and lower body) was measured using dual-energy x-ray absorptiometry (DEXA) and muscle and fiber cross-sectional area was measured using ultrasound and biopsy techniques, respectively. Lower body strength was assessed using leg-press one-repetition maximum (1RM).

Diets were monitored via a handful of 24-hour diet recalls conducted by a trained nutritionist (whatever that means) throughout the intervention. Total protein intake (as already mentioned) was supplemented (using soy or whey) to achieve an optimal recommendation to support resistance-training gains in muscle mass. Given the lower overall protein intake at baseline in the vegan group, they needed to supplement with slightly more protein to achieve the 1.6g/kg daily intake recommendation.

Results

At the end of the 12-week intervention, both groups increased their lower body muscle mass and lower body leg press 1RM strength with no differences between the groups. At the tissue-level, ultrasound and biopsies also showed no differences in muscle or fiber cross-sectional areas. Further, there were no differences in fiber-type distributions between the groups. Simply put, both groups gained nearly identical levels of strength and muscle mass regardless of diet and protein source.  

My commentary

First, the study design is strong with the inclusion of researcher supervised training sessions, highly accurate assessment methodologies for muscle mass accretion (biopsies, ultrasound and DEXA), and sufficient protein intake (set at 1.6 g/kg) to optimize the training stimulus. Dietary reporting, however, is certainly a limitation here, but it is hard to get around this without a highly expensive metabolic ward design. Three-day diet records rather than a handful of 24-hour recalls could have offered slightly more insight into dietary practices over the course of the study. (Oh well.)

Continuing on, the authors rightly acknowledged the lack of subject randomization, however, as already mentioned, this is understandable given the study question, so I do not see it as a huge limitation when you couple it with the fact that both groups were similar in almost each baseline characteristic (save vitamin D levels).

Another limitation levied against this study is its use of untrained subjects, which severely limits the generalizability of the findings to the well-trained population. Indeed, naïve trainees seem to increase strength and muscle mass on just about anything, regardless of dietary habits. Therefore, the question remains, “what would take place given a longer study duration?” Given the mechanistic data, greater differences might be realized between the diet groups given a long enough training period. This would obviously need to be verified or falsified with more investigation(s) in trained subjects.

Application and conclusion

Ultimately, if you are just starting a weight training program, this study lends credence to idea that overall protein intake is likely more important than diet/protein source when trying to build muscle mass and strength—assuming the training stimulus is sufficient. So if you prefer a plant-based diet, it doesn’t seem to matter a whole lot based on the data we have. From a ‘keep it simple stupid’ level of analysis, anything is better than nothing, so the mere fact of beginning a training program will obviously owe more to muscle mass and strength gains than just about any other factor. What remains to be seen is whether or not an exclusive plant-based diet is superior, inferior, or no different than an omnivorous diet for longer training periods or in those who are of (or achieved) a higher training caliber.

To be continued

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References

1.           Morton, R.W., et al., 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. 52(6): p. 376-384.

2.           Berrazaga, I., et al., The Role of the Anabolic Properties of Plant- versus Animal-Based Protein Sources in Supporting Muscle Mass Maintenance: A Critical Review. Nutrients, 2019. 11(8).

3.           Hartman, J.W., et al., Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. Am J Clin Nutr, 2007. 86(2): p. 373-81.

4.           Tang, J.E., et al., Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol (1985), 2009. 107(3): p. 987-92.

5.           Wilkinson, S.B., et al., Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr, 2007. 85(4): p. 1031-40.

6.           Yang, Y., et al., Myofibrillar protein synthesis following ingestion of soy protein isolate at rest and after resistance exercise in elderly men. Nutr Metab (Lond), 2012. 9(1): p. 57.

7.           Deane, C.S., et al., Animal, Plant, Collagen and Blended Dietary Proteins: Effects on Musculoskeletal Outcomes. Nutrients, 2020. 12(9).