Protein has always been a hot topic since it was discovered over a hundred years ago and we quickly learned it was an essential component for growth. Since then science has come a long way as we now know there are essential and non-essential amino acids and there is protein in all plants and animals.
It has been thought for a long time that animal protein is more “complete” than plants even though there have also been long-standing well-respected proponents (Walter C. Willett, M.D., Dr. P.H.) of plant protein being just as complete as animal protein. There has been a growing body of research on the completeness of plant protein for the purposes of muscle repair with some particularly new research from the past year.
In this article, we’re going to delve deep into how plant protein fares against animal protein for repairing muscle by looking at three critical areas of research not often covered together; amino acids composition, digestibility, and the latest research specifically comparing plant and animal protein for repairing muscle.
If you’ve been curious about how plant protein stacks up against other sources, or have struggled to understand which protein source is the right choice for you, this article is designed to help you make an informed decision and choose the protein that best supports you and your goals.
Amino Acid Composition
In the 1900s it was learned there were essential and non-essential amino acids and around the 1970s it was learned that animal products contained more essential amino acids than plant foods. For a while, it was thought, and it often still gets touted that because of this animal products are more complete and plant foods are missing some essential amino acids and for this reason, animal protein is “better”. In recent research, it has been proven that plant food isn’t missing any amino acids, essential or non-essential. 1
It is true the protein composition in different plants varies, however, the research on whether this results in general vegan populations consuming inadequate protein has not indicated vegans generally become deficient in any amino acids when they consume a variety of foods. It has been suggested that every meal has to be meticulously planned to ensure foods lower in one amino acid are combined with a food higher in that amino acid so no meal is low in any amino acid. The idea of foods needing to be combined was proposed by researcher, author, and strong vegetarian advocate (not vegetarian herself), Frances Moore Lappé, in her 1971 book Diet for Small Planet. 2,3
Institutions followed her recommendations, however, in the preceding decade she changed her stance on the necessity of “protein combining” and ensuing institutions followed suit but some are still slow to the game. 4 I think this quote from a recent publication in “Nutrient” addresses this concern quite well; “Overall, when diets are at least slightly varied, suggestions that vegetarians [vegans] to be sure to achieve a higher total protein intake than the RDA, or to pay strict attention to choosing plant foods with complementary amino acid patterns are simply over-precautious.” 5,6,7,8,9
Digestibility of Plant Protein
Understanding digestibility is typically the next area where individuals struggle when choosing protein sources, particularly the fear that plant proteins aren’t as “complete” as animal proteins. This is an area of science that has really not been conclusively researched and there have been major concerns to the validity of the science, however, there is new research that offers better insight into the question of just how well plant protein is digested compared to animal protein.
Protein digestibility has been assessed using two methods; protein digestibility corrected amino acid score (PDCAAS) and digestible indispensable amino acid score (DIAAS). There are several key flaws to the PDCAAS method that stems from the purpose of this system because it was designed to assess the lowest available amino acid in food which moreover addresses the needs of undernourished populations not developed nations where food variety is abundant and they most often eat multiple foods in a single meal, so this offers context to when it should be applied. 10
The DIAAS method has the advantage of being demonstrated with pigs, not rats, which have a similar digestive system and protein needs to humans. The DIAAS method still has a few flaws, however, it has the benefit of being able to access not just one food but multiple foods from a single meal at once which is obviously better because that’s actually how humans eat in developed countries. The major flaw with this method, same as PDCAAS, is it only uses raw foods which have been shown to greatly decrease the digestibility of nutrients and this is important because humans rarely eat meals of exclusively raw foods.
The best research we have is comparing true ileal digestion. This is a process that involves assessing the true digestion of the small intestine before it reaches the colon and is further digested by colonic enzymes. The research on this is very limited, however, the research suggests that soy and pea protein have true digestion of 91.5% while dairy protein has the highest protein digestion of 95%. 11 That’s a difference of only 3.5%. Let’s further qualify that by comparing dairy to soy and pea protein digestion using the recommended 1.7 (12 grams of protein) per day for endurance athletes also doing a moderate volume of strength exercises 13 :
70 (kg body weight) x 1.7 (dairy protein) = 119 grams of protein per day
70 (kg body weight) x (1.7 (pea or soy protein) x 3.5%) = 123 grams of protein per day
Muscle Repair
Animal protein, particularly dairy (whey protein), has been studied and come to be accepted as the best for repairing muscle due to it having the highest quantity of leucine per calorie and other amino acids and highest efficiency of digestion. It is thought because of these it has most often been shown to cause the greatest rate of muscle protein synthesis (MPS). Most people hear and see dairy causing the greatest MPS and think “dairy is obviously best for muscle repair”. It’s worth considering that studies have shown if you consume a plant-based meal that is matched for calorie, leucine, and total protein, older adults achieve the same rate of MPS and in young healthy resistance-trained adults they may even achieve a higher rate of MPS than those who consume dairy protein. 14,15
This still isn’t the whole story. Rarely are studies that actually compare actual strength and muscle mass gains between those consuming dairy protein and plant protein. People usually stop at the mechanism without thinking that mechanisms may not actually lead to real human differences. In the world of athletic performance shouldn’t this be almost only what we look at before considering to base our dietary choices on anything?
Let’s look at some specific studies on trained and untrained populations…
This study on 3100 older adults found that 1.3 grams of protein per kg of body weight from both plant or animal protein are associated with similar skeletal muscle mass and may be able to prevent sarcopenia. 16
This study found that when matched for total protein (not leucine) pea protein produced a statistically significant increase in bicep brachii muscle thickness in young resistance-trained males while the whey protein did not, against the placebo. 17
This study on healthy resistance-trained male subjects found that when total daily grams of protein per kg of body weight and total post-workout protein intake was matched subjects experienced similar improvements in strength when given pea or whey protein post-workout, even though the whey protein had 22% more leucine than pea protein which is likely due to pea protein still providing just over 2g of leucine per serving. 18
This study found similar improvements in functional training performance on 15 male subjects when consuming a 24-gram total protein matched supplement of pea or whey protein over an 8-week period, however, researchers noted even though subjects achieved a desirable 1.7 grams of protein per kg of body weight they would have experienced greater improvements if they consumed more than 2,000 Kcals per day. 19
This 2018 meta-analysis concluded, “In conclusion, the current meta-analysis is consistent with the totality of the evidence regarding protein supplementation and RET. Our meta-analysis identified that soy foods and soy protein supplements can be viewed as sources of protein suitable for building strength and increasing lean tissue in response to RET. Overall, the results indicate that protein source is not likely an important factor influencing gains in strength and LBM in response to RET.” 20
This most recent June 2020 study found no significant difference between strength and muscle mass gains among 61 untrained young male subjects when prescribed to consume a leucine matched (not total protein) supplement of 2 grams per serving post-exercise during a 12-week resistance training program. 21
You might be thinking, “Is all this protein education necessary?” Well, a study from 2011 on collegiate level resistance-trained athletes during which they were surveyed on what they thought their protein needs to be indicated that on average they thought their protein needs were 21 grams of protein per kg of body weight. 22 That’s 19 grams more per kg of body weight than what is the maximum beneficial quantity!
If you’re an athlete or a professional who works with athletes, this may be a reason to consider how you talk about protein with athletes, as to not fuel the already protein-crazed society most of us live in.
Conclusion
If you’ve considered a more plant-based diet, or have struggled to adequately fuel yourself on a plant-based diet, I’d like to briefly address the adequacy of a vegan diet to provide enough protein. Keep in mind that studies show while some vegan populations do undereat protein, it is primarily because they don’t eat enough variety of foods, namely legumes. 23 I hope this helps relieve any concerns regarding plant protein adequacy and helps to improve nutrition literacy so as people and athletes we can make more informed decisions about our nutrition choices, our health, and how we fuel ourselves to reach our full potential.
About the Author:
Coach Carson is a dedicated athlete and coach based in Tasmania, Australia who specializes in cycling, strength, and conditioning, and finding a balanced and sustainable approach for his athletes. For more information on Carson’s coaching services, or to schedule a coaching consultation with him click HERE.
Resources:
1 https://www.idosi.org/wasj/wasj30(1)14/15.pdf
2 https://en.wikipedia.org/wiki/Diet_for_a_Small_Planet
3 https://en.wikipedia.org/wiki/Frances_Moore_Lapp%C3%A9
4 https://www.drmcdougall.com/misc/2007nl/apr/protein.htm
5 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6893534/
papers/vegetarian-diet.pdf
7 https://www.drmcdougall.com/misc/2004nl/040100puproteinoverload.htm
8 https://www.drmcdougall.com/misc/2003nl/dec/031200puprotein.htm
9 https://www.mja.com.au/journal/2013/199/4/protein-and-vegetarian-diets
10 https://academic.oup.com/jn/article/130/7/1865S/4686203
11 https://journals.sagepub.com/doi/pdf/10.1177/156482651303400225
12 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5867436/
13 https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0177-8
14 https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/abs/mycoproteinbased-high protein-vegan-diet-supports-equivalent-daily-myofibrillar-protein-synthesis-rates-compared-with-an-isonitrogenous-omnivorous-diet-in-older-adults-a-randomised-controlled-trial/EBE0DBC26F4174801BBA671621B183C9
15 https://academic.oup.com/ajcn/article/112/2/318/5841182
16 https://jandonline.org/article/S2212-2672(18)31397-2/fulltext#bib48
17 https://jissn.biomedcentral.com/articles/10.1186/s12970-014-0064-5
18 https://jissn.biomedcentral.com/articles/10.1186/s12970-020-00394-1
19 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6358922/
20 https://journals.humankinetics.com/configurable/content/journals$002fijsnem$002f28$002f6$002fartic
le-p674.xml?t:ac=journals%24002fijsnem%24002f28%24002f6%24002farticle-p674.xml
21 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7312446/
