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Evidence-based Nutrition

  • Writer's pictureDr Roxie Becker

Is Plant Protein Really Inferior to Animal Protein?

Updated: Dec 19, 2022


Photo by Polina Tankilevitch from Pexels

“But where do you get your protein?” Is the most commonly asked question I receive. And subsequently “But surely meat is better than plants for building muscle?”, which is said more as a statement of fact rather than a question. There are many myths about vegan protein and this article aims to address them.


How much protein do we actually need?

Generally, you’ll find two groups of vegans. Those that believe as long as you consume sufficient calories, you’re fine, and those that believe you should be drinking protein shakes and eating mock meats every day to compensate for the fact that you’re eating a lower quality of protein by choosing plant-based sources over animal sources.


The answer to the above question depends on your goal. If you are a relatively sedentary person who is not seeking to gain or to lose weight, then 0.8g protein/kg/day should suffice, which is the Recommended Daily Allowance. You should be able to obtain this from eating sufficient calories from whole foods each day. However, if you are an athlete or have the goal of building muscle, then your daily requirements obviously increase.


The International Society of Sports Nutrition published their recommendations in review in 2017. Their recommendations are as such:(1)

  • Athletes should generally aim for 1.4-2.0g/kg/day. It has been suggested that endurance athletes aim for the lower end of the range, while bodybuilders, powerlifters and other strength-focused athletes aim for the higher end

  • Higher protein intakes between 2.3-3.1g/kg/day may be used to maximize lean muscle mass retention when an athlete is in a caloric deficit, for example, when a bodybuilder is leaning out for a show

  • Even higher protein intakes >3.0g/kg/day may be beneficial for advanced lifters and promote loss of fat mass and gain of lean muscle mass


Are plant proteins complete?

A common myth surrounding plant proteins is that they are incomplete, meaning they do not contain all of the essential amino acids. There are 20 amino acids we consume; there are 11 non-essential amino acids, namely alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine, that the body can synthesize if it doesn’t get enough from the diet, and 9 essential amino acids, namely histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine, which the body cannot synthesize and therefore need to be obtained from the diet. All plant-based foods contain all of both the essential and the non-essential amino acids in varying amounts.(2) The notion that plants are "incomplete proteins" because they do not contain all the essential amino acids has long been dispelled.


From article: Maximizing the intersection of human health and the health of the environment with regard to the amount and type of protein produced and consumed in the United States. (See reference 2).

Do you need to eat more protein if you’re vegan?

Something you may have heard is that if you are consuming a plant-based diet, you need to aim for the upper ends of these ranges, or even higher, because plant protein is less digestible than animal protein.


There are two main scoring systems that are used to measure protein quality; the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and the Digestible Indispensable Amino Acid Score (DIAAS). If you examine these scoring systems, you will note that various meat and dairy products typically score higher than plant-based sources of protein, such as legumes, tofu, nuts and seeds. However, there are some issues with these scoring systems.


Firstly, there are based on pig and rat intestines, which do substantially vary from human intestines, in terms of length, gastric pH, intestinal motility, GI transit time, gut microbiome flora etc, which all impact digestion.(3)


Secondly, they are based on the limiting amino acid. Both of these scores factor in 2 variables:

  1. the digestibility i.e. the ratio of protein consumed vs protein absorbed

  2. the amount of essential amino acids per gram of protein compared with the ideal amount, and this second number is based on the limiting amino acid

Let’s look at the example of raw basmati rice.(4)


It has a PDCAAS score of 0.7 out of 1. If we look at the first diagram, we can see that lysine, in orange, is the limiting amino acid, present in the lowest amount, which is why it’s used to calculate the PDCAAS score. The amino acids score (AAS) is 77%, as seen in red in the table, which is the ratio of 37mg of lysine in 1g of protein in basmati rice vs the 48mg of lysine per 1g of ideal protein. The protein digestibility (how much protein is absorbed) is 91%. If you multiple 0.77 x 0.91 you get to a PDCAAS score of 0.70.


The problem with using the limiting amino acid is that this is assuming you are getting all your daily protein from a single source. However, if you consume a variety of food sources throughout the day, they compensate for each other. For example beans generally have a lysine amino acid score of more than 100%. So it compensates for the lower lysine found in rice.


And thirdly, they often use raw foods to calculate these scores, as seen in this example. Which is an issue since cooking foods such as whole grains and beans increases the bioavailability of the protein.(5)

If you use oro-ileal digestibility in humans, which is the most accurate measurement to date, animal and plant proteins vary by only a few percent, with the majority hovering between 90-94% digestibility (both plant and animal). So there really is no need to consume additional protein simply because you’re eating a plant-based diet.(6)


Does this theory hold true in practice?

More and more research is being published showing no difference in the strength or muscle mass gains of those who consume animal- vs plant-based diets.


A study published in 2021(7) that looked at 19 individuals on an iso-caloric high protein diet consuming 1.8g/kg/day of protein. One group consumed predominantly animal protein, and the other group was exclusively vegan, obtaining most of their protein from mycoprotein – commonly found in Quorn products. And they found that the myofibrillar protein synthesis, calculated from muscle biopsies, though slightly higher in the vegan group, showed no significant difference.


Another study(8) looking at rice protein took 24 males who were resistance-trained, were matched on high protein diets (1.6-1.8g/kg/day protein) with half randomized to consume 24g rice protein powder daily, and the other half to consume whey protein, while participating in an 8 week resistance training program. And again, at the end of this period, there were no significant differences in the changes in their in their lean muscle mass or one rep maxes.


Regarding soy protein, another study published in 2021(9) looked at habitual vegans and omnivores (following their preferred diet for a minimum of 1 year preceding the study). They were matched on high protein diets and followed a 12 week resistance training program, while the vegans supplemented with a soy protein powder and the omnivores with a whey protein powder. This study concluded that there was no significant differences between the improvements in lean muscle mass, muscle size or one rep max strength.


In conclusion, plant proteins have always been viewed as inferior to animal proteins regarding building muscle and strength, however, we are accumulating more and more research that suggests that this gap is not nearly as large as previously thought.

References


  1. Jäger R. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14(20).

  2. Gardner CD, Hartle JC, Garrett RD, Offringa LC, Wasserman AS. Maximizing the intersection of human health and the health of the environment with regard to the amount and type of protein produced and consumed in the United States. Nutr Rev. 2019 Apr 1;77(4):197-215.

  3. Kararli TT. Comparison of the gastrointestinal anatomy, physiology, and biochemistry of humans and commonly used laboratory animals. Biopharmaceutics & drug disposition. 1995;16:351-380.

  4. Images: 2000kcal. Protein Quality Evaluation and Protein Combining: Visual tools for the PDCAAS method. 2000. Example 2. Available: ttps://www.2000kcal.cz/lang/en/static/protein_quality_and_combining_pdcaas.php [Accessed 28.01.2022]

  5. Drulyte D, Orlien V. The Effect of Processing on Digestion of Legume Proteins. Foods. 2019;8(6):224.

  6. Mariotti F, Gardner CD. Dietary Protein and Amino Acids in Vegetarian Diets—A Review. Nutrients. 2019 Nov; 11(11): 2661.

  7. Monteyne AJ, Dunlop MV, Machin DJ, Coelho MOC, Pavis GF, Porter C, Murton AJ, Abdelrahman DR, Dirks ML, Stephens FB, Wall BT. A mycoprotein-based high-protein vegan diet supports equivalent daily myofibrillar protein synthesis rates compared with an isonitrogenous omnivorous diet in older adults: a randomised controlled trial. Br J Nutr. 2021 Sep 14;126(5):674-684.

  8. Moon, J.M., Ratliff, K.M., Blumkaitis, J.C. et al. Effects of daily 24-gram doses of rice or whey protein on resistance training adaptations in trained males. J Int Soc Sports Nutr 17, 60 (2020).

  9. 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. 22021;51:1317–1330.



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