When I transitioned to a plant based diet many years ago, the question I got asked most was how on earth was I going to eat enough protein?
Several years on, having miraculously retained my muscle mass, it’s a question I get asked much less frequently.
Today there is a better understanding that plants do provide all the protein required for us humans, as the myths surrounding ‘high quality’ animal protein slowly get squashed.
Nevertheless, some of these myths still persist, as well as uncertainty about meeting protein requirements with a plant-based diet.
Here I go through the science that shows us how plant protein is more than adequate to meet our needs, and may actually be the best protein source out there.
The importance of protein
Protein is crucial for growth, maintenance, and repair of the body, especially our bones and muscles.
Proteins are made up of around 20 different amino acids. 11 of these can be made by the body whereas the other 9 are essential amino acids, because they must be provided by the food we eat.
The essential amino acids are:
The body breaks down the protein we eat into individual amino acids. These go into the amino acid pool, where the ones we need get absorbed and used by our cells, to build proteins and some other large molecules. The ones we don’t need are flushed out in the urine. Amino acids are a bit like lego pieces, they can be put together in different orders, using different amounts, to form different structures (proteins).
On average, we need about 0.8 grams of protein per kilogram of body weight daily, so someone who weighs 70kg needs to consume 56 grams of protein a day. This can increase in people who are physically active, and in the elderly to prevent muscle loss and conditions like sarcopenia 1.
The body can’t store protein, so once your needs are met, any excess is stored as fat. For this reason it’s advised to stick to these recommendations and not overdo the protein.
For a long while, meat, dairy and eggs were considered the best protein sources, but this is changing.
Busting protein myths
In a recent review, Dr David Katz, past president of the American College of Lifestyle Medicine, stated that “the definition of protein quality [that promotes meat, eggs and dairy] is both misleading and antiquated” 2.
Animal protein has long been considered as a high quality protein source because it’s a ‘complete protein’. This means it contains all 9 essential amino acids, compared to plant proteins which are often lower in one essential amino acid 3. Grains, for example, tend to be lower in lysine, and legumes tend to be lower in methionine 4.
But as Dr David Katz discusses in his review, the idea that this makes plant protein of lower quality is outdated, and basically nonsense.
You can get all the essential amino acids from plants, you just need a variety of plant sources in your diet. This is an important aspect of any healthy diet regardless of protein concerns. You wouldn't consume a diet based solely on legumes (unless you really like legumes) so this variety is natural and not something to worry about. After all, isn’t variety the spice of life?
Eating a range of plant foods over a day, or even several days, will still give you all the essential amino acids you need 2.
There are also some ‘complete’ sources of plant protein for those who want to get the most bang for their buck. Soya, quinoa, chia seeds, and buckwheat contain all 9 essential amino acids.
Switch to plant protein and ditch disease
We know that plant protein provides all the amino acids that meat provides, but why should you switch on this basis?
Numerous studies now show us that plant protein is actually much better for our health than animal protein.
Animal protein comes packaged with saturated fat and other disease-promoting components, such as heme iron and advanced-glycation end products generated via cooking. Whereas plant protein is nicely wrapped in protective elements such as fiber, antioxidant vitamins and phytochemicals 5.
These elements mean their consumption is related to different disease outcomes.
Plant protein is associated with a significantly reduced risk of dying from cardiovascular disease compared to animal protein, a finding that has been replicated in several large studies 6 7 8.
One study found that the consumption of red meat protein in women is associated with a greater risk of coronary heart disease, where just one serving per day of nuts instead of a serving of red meat can reduce the risk of coronary heart disease by 30% 9.
And it’s not just cardiovascular disease that is provoked by animal protein.
Animal protein is linked to both insulin resistance and an increased likelihood of developing type 2 diabetes, whereas plant protein is associated with a reduced risk of type 2 diabetes 10 11. In one cohort study, there was a 22% increase in type 2 diabetes in the group consuming the most animal protein, compared to those consuming the least 12.
Even partly replacing meat protein with soy protein improves insulin sensitivity, the driver of type 2 diabetes, which could prevent metabolic syndrome 13
Then we come to cancer research.
In a real-world study looking at over 70,000 adults, getting rid of red and processed meat protein and replacing it with plant protein significantly lowered the risk of death from cancer 14.
This may be because of a decrease in circulating levels of a hormone called insulin-like growth factor 1 (IGF-1). Animal protein stimulates the production of IGF-1, which is crucial for cell growth and increases the risk of cancer development when present in high amounts. So an increase in plant protein and reduction in animal protein may reduce cancer risk by decreasing levels of IGF-1 and boosting the body’s natural cancer defenses 15.
In another study looking at 44,824 adults, replacing animal protein with plant protein was associated with around a 30% risk reduction of developing rectal cancer 16.
Sources of plant protein
Nuts and legumes are excellent sources of protein. For example, peanuts have the same amount of protein as beef, both have 26g of protein per100g .17.
Tofu, tempeh, and edamame all originate from soybeans and are great, diverse sources of plant protein.
I enjoy making a simple scrambled tofu for breakfast or adding extra veggies and having it for lunch or dinner. This is a great way to replace animal protein (eggs) with plant protein whilst enjoying a delicious and familiar meal.
The bottom line
The issue with protein is hugely overstated in developed countries such as the US and UK.
Eating a varied diet that contains fruits, vegetables, legumes, nuts and seeds easily provides you with all of the protein you need.
Besides, how often do you hear anyone talk about protein deficiency in the US, compared to the alarming cases of cancer, heart disease, obesity and type 2 diabetes? 18. Not very often, because protein deficiency is rare compared to the issues linked to animal protein consumption 19.
It’s time we stopped focusing on the amount of protein, and started focusing on quality plant sources that provide all the amino acids we need, along with added protective effects against disease.
1. Paddon-Jones, D. et al. Protein and healthy aging. Am. J. Clin. Nutr. 101, 1339S-1345S (2015).
2. Katz, D. L., Doughty, K. N., Geagan, K., Jenkins, D. A. & Gardner, C. D. Perspective: The Public Health Case for Modernizing the Definition of Protein Quality. Adv. Nutr. 10, 755–764 (2019).
3. Tomé, D. Digestibility Issues of Vegetable versus Animal Proteins: Protein and Amino Acid Requirements—Functional Aspects. Food Nutr. Bull. 34, 272–274 (2013).
4. Galili, G., Amir, R., Hoefgen, R. & Hesse, H. Improving the levels of essential amino acids and sulfur metabolites in plants. Biol. Chem. 386, (2005).
5. Afshin, A., Micha, R., Khatibzadeh, S. & Mozaffarian, D. Consumption of nuts and legumes and risk of incident ischemic heart disease, stroke, and diabetes: a systematic review and meta-analysis. Am. J. Clin. Nutr. 100, 278–288 (2014).
6. Tharrey, M. et al. Patterns of plant and animal protein intake are strongly associated with cardiovascular mortality: the Adventist Health Study-2 cohort. Int. J. Epidemiol. 47, 1603–1612 (2018).
7. Qi, X.-X. & Shen, P. Associations of dietary protein intake with all-cause, cardiovascular disease, and cancer mortality: A systematic review and meta-analysis of cohort studies. Nutr. Metab. Cardiovasc. Dis. 30, 1094–1105 (2020).
8. Naghshi, S., Sadeghi, O., Willett, W. C. & Esmaillzadeh, A. Dietary intake of total, animal, and plant proteins and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies. BMJ m2412 (2020) doi:10.1136/bmj.m2412.
9. Bernstein, A. M. et al. Major Dietary Protein Sources and Risk of Coronary Heart Disease in Women. Circulation 122, 876–883 (2010).
10. McMacken, M. & Shah, S. A plant-based diet for the prevention and treatment of type 2 diabetes. J. Geriatr. Cardiol. JGC 14, 342–354 (2017).
11. Virtanen, H. E. K. et al. Intake of different dietary proteins and risk of type 2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Br. J. Nutr. 117, 882–893 (2017).
12. van Nielen, M. et al. Dietary Protein Intake and Incidence of Type 2 Diabetes in Europe: The EPIC-InterAct Case-Cohort Study. Diabetes Care 37, 1854–1862 (2014).
13. van Nielen, M., Feskens, E. J. M., Rietman, A., Siebelink, E. & Mensink, M. Partly Replacing Meat Protein with Soy Protein Alters Insulin Resistance and Blood Lipids in Postmenopausal Women with Abdominal Obesity. J. Nutr. 144, 1423–1429 (2014).
14. Budhathoki, S. et al. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality in a Japanese Cohort. JAMA Intern. Med. 179, 1509 (2019).
15. Sieri, S. et al. Dietary Intakes of Animal and Plant Proteins and Risk of Colorectal Cancer: The EPIC-Italy Cohort. Cancers 14, 2917 (2022).
16. Madigan, M. & Karhu, E. The role of plant-based nutrition in cancer prevention. J. Unexplored Med. Data 3, 9 (2018).
17. Williams, K. A. & Patel, H. Healthy Plant-Based Diet. J. Am. Coll. Cardiol. 70, 423–425 (2017).
18. Song, M. et al. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA Intern. Med. 176, 1453 (2016).
19. Berryman, C. E., Lieberman, H. R., Fulgoni, V. L. & Pasiakos, S. M. Protein intake trends and conformity with the Dietary Reference Intakes in the United States: analysis of the National Health and Nutrition Examination Survey, 2001–2014. Am. J. Clin. Nutr. 108, 405–413 (2018).