Plant Proteins Explained
Updated: Mar 8, 2022
We hear that vegetable proteins are incomplete. Yes, it's true. Is it a problem? With the information in this text, you will be able to understand what a protein is and then answer the question.
What is a protein
It’s a macronutrient that gives energy. Also, proteins are used to maintain and develop our tissues, help chemical reactions in our body take place, help form antibodies to fight infections, and much more (Healthline, 2018).
Primary protein structure:
(National Human Genome Research Institute, 2004)
With this picture where the chain represents the primary protein structure, we can imagine that it takes all the little beads to build a protein. These beads are amino acids. Our proteins need 20 different amino acids to be built and functional. Of these 20 amino acids, 9 cannot be produced by the human body and must therefore come from the food we eat. These amino acids are said to be essential; if any of these are missing from our diet, it is impossible for our body to build new protein.
Sources of protein
Animal (egg, beef, poultry, milk, fish, etc.) : They have all 9 essential amino acids in the proportions that our body needs. So we say they are complete.
Plant (soy, quinoa, legumes, lentils, nuts, etc.) : Depending on the source, proteins can have all 9 essential amino acids, but with different proportions and insufficient for our body.
Not all sources of plant protein are created equal. Some sources may lack completely or partially one or more different amino acids. That is why they are considered incomplete. That's okay, just combine plant protein throughout the day to remedy the lack of one or more amino acids in a protein source. It doesn't have to be at the same meal and it is unnecessary to know which amino acid(s) is or are limiting in our protein sources. By varying our protein sources, our body will have all the essential amino acids in good quantities. In addition, we probably already do it since it is rare that we eat the same foods at all meals.
Example to meet all our needs in essential amino acids
Need vs amount of vegetable protein eaten
It is possible that a source of plant protein has a limiting amino acid. That is, an amino acid that may be present, but in an amount that is not ideal for our body. To counteract this problem, we can eat more of this food to meet our needs or take other protein foods throughout the day to meet all our amino acid needs.
Take tofu as an example which is a good vegetable source of protein. The following table was taken from vegfaqs.com which shows the essential amino acid requirements for a day for an average 65 kg person versus the amount of amino acid contained in a regular block of tofu. So if an average person eats a block of tofu, they will have approximately 65% of their needs for methionine and cystine (amino acids) and 100% of the other 7 essential amino acids. If this same person eats one block and a half of tofu, 100% of her needs for the 9 essential amino acids will be met.
In fact, the protein requirement for a sedentary person at a healthy weight needs a minimum of 0.8 g / kg of body weight per day (HHP, 2022). So, if we take a tablespoon of protein foods a day, whether from animal or vegetable sources, we will run out of amino acids to build our proteins. On the other hand, in Canada and in most industrialized countries, it is very rare not to eat enough protein
Amino acids are absorbed in the small intestine. Food takes around 6 to 8 hours to pass from the mouth to the end of the small intestine (Elizabeth Rajan, M.D, 2019). By eating only 3-5 meals or snacks a day, about 4-8 hours apart, we have amino acids available to make new proteins. We are constantly absorbing amino acids that are available to us to make proteins. So if we eat oatmeal and nuts for lunch and eat tofu for dinner, we wouldn't lack amino acids to make our proteins if we eat a reasonable amount of food. You don't have to think about the amino acids that are limiting in the different sources of plant protein in order not to run out. Naturally, we eat varied protein food sources, so we will meet our essential amino acid needs.
On the other hand, our body is breaking down and remaking proteins in our body continually. This puts available some amino acids needed to make new proteins up to a certain limit. The amino acids that are available by breaking down our proteins and those ingested with our food are used to make new proteins.
So if we take a variety of protein sources throughout the day, we will not lack amino acids to build our beautiful proteins. You don't need to eat multiple sources of protein in one meal. Finally, anyone who has a varied vegetable diet, respecting an adequate intake of calories (energy) will not be deficient in amino acids.
I hope it is clearer for you and that you have learned something.
Have a good day,
Karine Drouin RD
Thanks to Gabrielle Grenier who gave me genuine support towards writing this text.
Academy of Nutrition and Dietetics. (2016). Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. Journal of the Academy of Nutrition and Dietetics. 116.(12), 1970-1980. Doi: 10.1016/j.jand.2016.09.025.
Cudmore, D. (2020). Is Tofu a Complete Protein? (i.e. Soy). Retrouvé le 18 décembre 2020 au
Pendick, D. (Janvier, 2022). How much protein do you need everyday? Harvard Health Publishing. Retrouvé le 8 mars 2022 au https://www.health.harvard.edu/blog/how-much-protein-do-you-need-every-day-201506188096
Rajan, E. (2019) Retrouvé le 18 décembre 2020 au https://www.mayoclinic.org/digestive-system/expert-answers/faq-20058340
Rayaprolu, S., Hettiarachchy, N., Horax, R. et al. (2015). Amino Acid Profiles of 44 Soybean Lines and ACE-I Inhibitory Activities of Peptide Fractions from Selected Lines. J Am Oil Chem Soc 92, 1023–1033. Doi: 10.1007/s11746-015-2655-y
Van De Walle, G. (2018). 9 Important Functions of Protein in Your Body. Healthline. Retrouvé le 25 décembre 2020 au https://www.healthline.com/nutrition/functions-of-protein#TOC_TITLE_HDR_8