The fear of protein deficiency is one of the oldest and most persistent barriers to adopting a plant-based diet.
When I decided to give up meat thirty-five years ago, this was the objection I heard most often from family, friends, and even some professors at the Faculty of Medicine.
Myth: Vegetarians don’t get enough protein.
There are two aspects to adequate protein intake: one quantitative and one qualitative. Quantitatively, the Recommended Dietary Allowance for adults is 0.8 g/kg/day. To address the qualitative aspect, it is essential to understand a few things about protein.
The role and importance of protein in the body
There are over 90,000 proteins in the human body, each with a specific function. Collagen, found in bones, skin, muscles, and tendons, and keratin, found in nails and hair, are examples of proteins with structural functions. There are also proteins with functional roles, such as digestive enzymes like pepsin and lipase, which help to break down food, haemoglobin, which transports oxygen from the lungs to all tissues, hormones like insulin, and antibodies produced by the immune system to fight infectious diseases, and so on.
In order to perform this incredible diversity of functions, proteins are constructed in an extremely ingenious way. Imagine a protein molecule as a sentence or phrase made up of words, which in turn are made up of combinations of letters. In the world of proteins, these “letters” are represented by 20 amino acids, which are linked together in sequences unique to each protein. These sequences are assembled according to instructions transcribed from DNA in the nucleus into messenger RNA, which is directed to ribosomes—cellular structures that produce proteins according to the information encoded in the messenger RNA.
Ribosomes require all 20 amino acids in varying quantities to maintain the production of necessary proteins. Nine of these amino acids are called essential because the body cannot produce them and must obtain them from food.
Plant sources, a good choice
Plant sources of protein have often been considered “incomplete” because they do not contain sufficient amounts of at least one of the essential amino acids. For example, grains contain less lysine than an adult needs. Legumes have slightly lower levels of methionine and cysteine (sulphur-rich amino acids). However, these levels would only become problematic if someone ate only grains or legumes every day. In reality, however, most people in developed countries have a varied diet, so their total protein and essential amino acid intake usually exceeds their daily requirements (Mariotti and Gardner, 2019).
Therefore, concerns about possible protein or essential amino acid deficiencies in vegetarians are unfounded if their diet is varied. It is important to consume a wide range of plant foods from all groups (grains, legumes, nuts, seeds, fruits, and vegetables) in amounts appropriate to one’s energy needs.
Unilateral, highly restrictive diets can be problematic. Population studies, such as the EPIC-Oxford study, confirm this, showing a downward trend in protein consumption according to the following order: meat eaters > fish eaters > ovo-lacto vegetarians > vegans (Sobiecki, Appleby et al., 2016).
However, vegetarians with a varied diet do not have this problem. For example, the Adventist Health Study 2, which was conducted on a sample of over 90,000 Adventists in the US, found that protein consumption among vegans was similar to that of omnivores or lacto-ovo vegetarians (Rizzo, Jaceldo-Siegl et al., 2013). This was largely due to frequent consumption of protein-rich plant foods, such as legumes, nuts, seeds, and whole grains.
I invite you to watch a video I recently made for more details on this topic, in which I demonstrate how you can meet the daily protein requirements (quantitative and qualitative) of an adult female with less than 1,000 calories from just nine exclusively plant-based foods (link to video: https://www.youtube.com/watch?v=7suBBLBtP2k).
Bibliography:
- S. Rizzo, K. Jaceldo-Siegl et al., “Nutrient profiles of vegetarian and non-vegetarian dietary patterns”, Journal of the Academy of Nutrition and Dietetics, Vol. 113, No. 12, December 2013, pp. 1610–1619.
- Mariotti, F. and Gardner, C. D., “Dietary protein and amino acids in vegetarian diets: a review,” Nutrients, Vol. 11, No. 11, November 2019, Art. No. 2661.
- G. Sobiecki, P. N. Appleby, et al., “High compliance with dietary recommendations in a cohort of meat eaters, fish eaters, vegetarians, and vegans: results from the European Prospective Investigation into Cancer and Nutrition–Oxford study,” Nutrition Research, Vol. 36, No. 5, May 2016, pp. 464–477.
Gily Ionescu is a specialist in internal medicine and infectious diseases, as well as a nutritionist. He works as an internist at the Walla Walla Clinic in Washington State, USA, where he lives with his wife and two children. He completed the Master of Science in Nutrition and Wellness programme at Andrews University in Michigan, USA, in 2004. You can find all the videos he’s made on YouTube under @DrGilyIonescu.