By Mario Meouchi
When mentioning dietary protein, the first thing that comes to mind may be a nice cut of meat. In fact, for the majority of people, meat makes up an important part of their diet and for a good reason: it is a complete protein. Now arises the question of what defines a complete, or otherwise incomplete protein.
A complete protein is an article of food containing all of the essential amino acids, meanwhile, an incomplete protein is an article of food that contains up to eight of the nine essential amino acids. The essential amino acids include isoleucine, leucine, histidine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They represent amino acids that the body is unable to produce fast enough to keep up with the demands of the body or is unable to synthesize altogether. The non-essential amino acids include arginine, alanine, asparagine, cysteine, glutamic acid, proline, glycine, aspartic acid, glutamine, serine, and tyrosine. Non-essential amino acids can be produced by the body thus making their presence in the diet not nearly as important as that of the essential amino acids. Examples of complete protein include beef, poultry, fish, eggs, dairy and soy, on the other hand nuts, seeds, beans and some grains are classified as being incomplete proteins.
Meat, among other animal-based proteins, has held its importance throughout history, but with the recent surge in popularity of vegetarian and vegan diets, can plant-based protein prove to be viable? This question has been tackled by Gorissen, S.H.M., a grant advisor and project manager at Zuyderland Academy (with Zuyderland being a Dutch medical center), et al. in a paper published in 2018.
Fig. 1 Mean protein content of plant-based food articles (white bars), animal-based food articles (grey bars) and human muscle (black bar). | Gorissen, S.H.M et al., 2018, Protein Content and Amino Acid Composition of Commercially Available Plant-based Protein Isolates.
The protein contents measured in Fig. 1 were determined using the Dumas Combustion Method which processes organic matter to be broken down into carbon dioxide, water and gaseous nitrogen, the latter of which is used to determine the protein content. The protein contents were multiplied using the same conversion factor of 6.25 in order to enable direct comparisons.
The trend has shown that if human muscle was considered as the optimal protein content, then animal proteins are generally closer to being optimal compared to plant-based proteins. This may support the claim that animals are still a better source of protein, but the advantage of plants is their sheer diversity. Although it is true that Caseinate (a protein derived from skim milk) outperforms Corn, Hemp, Oat and Lupin, it is also true that concentrated Potato protein, Brown Rice and Pea come close in terms of protein content and may be considered a good alternative protein source.
Fig. 2 Mean essential amino acid content of plant-based food articles (white bars), animal based food articles (grey bars) and human muscle (black bar). The dashed line represents to amino acid requirement of adults | Gorissen, S.H.M et al, 2018, Protein Content and Amino Acid Composition of Commercially Available Plant-based Protein Isolates.
Fig. 3 The mass of raw material needed to provide 2.7g of Leucine or 10.9g of essential amino acids across different food articles. | Gorissen, S.H.M et al, 2018, Protein Content and Amino Acid Composition of Commercially Available Plant-based Protein Isolates.
According to Fig. 2, animal-based proteins contain high enough amounts of essential amino acids to satisfy the daily needs of an adult, whereas the same mass would be insufficient for some of the plant-based proteins such as Oat and Lupin, while others such as Corn and Pea surpassed the threshold. It shows us that it is entirely possible to obtain our daily needs of essential amino acids purely from plant-based proteins.
Moreover, Fig. 3 shows us that in order to obtain 2.7g of Leucine, compared to the required 35g of Caseinate, requiring 105g of Hemp would make it a significantly worse source of the aforementioned amino acid. However, it is important to note that the diversity of plants shines yet again, as Corn requires 31g to be ingested to meet the 2.7g of Leucine threshold, making it equal if not slightly better as a Leucine source compared to Caseinate.
If we would like to acquire 10.9g of essential amino acids, taking Caseinate as the baseline yet again with 33g of it providing enough essential amino acids, this time Corn would be considered inferior, requiring 52g, whereas concentrated Potato protein requires 37g. The latter would be considered a source of essential amino acids that is almost equal in quality compared to Caseinate.
Now why have 2.7g of Leucine and 10.9g of essential amino acids been chosen as reference points? It is because they have been shown to be the minimum amount required to stimulate muscle synthesis which is quite crucial considering that if a diet does not trigger this process, it would not be considered to be a viable option. Muscles requiring so much protein to be sustained is the same reason as to why something like bodybuilding emphasizes so much on protein intake.
There is no secret in maintaining a viable plant-based diet that meets all of one’s daily protein needs other than diversity. As previously shown, where one source may be lacking, another one can cover, such as in the case of Corn being high in Leucine and low in essential amino acids and concentrated Potato protein being high in essential amino acids. Eating too much of one singular protein will inevitably lead to a deficiency in one nutrient or the other. Considering how some plant-based protein sources contained nearly similar percentages of overall protein compared to animal-based protein sources, it is important to remember just how plants have shown great diversity, especially in their contents, a diet equally diverse could make being a vegetarian or a vegan a healthy and simple alternative. The diverse diet could even prove to be enjoyable as with a great number of ingredients, one can make a great number of tasty dishes.
Reference(s):
Gorissen, S.H.M., Crombag, J.J.R., Senden, J.M.G. et al. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids 50, 1685–1695 (2018). https://doi.org/10.1007/s00726-018-2640-5