We need protein because it is a vital component of our muscles, hair, nails and collagen – a connective tissue protein that holds your body together. Protein is also needed to make your brain’s messengers (neurotransmitters), hormones, red blood cells and DNA. Another important role that protein plays is in maintaining a healthy immune system.
But not all protein is created equal. Each protein molecule is made up of small building blocks called amino acids. We can make some amino acids ourselves but there are nine that the body cannot make, so they must be obtained from the diet. These are called essential amino acids. A varied plant-based diet provides more than enough protein and all the essential amino acids in sufficient amounts (1, 2, 3, 4).
The protein combining myth
All plant wholefoods contain all essential amino acids. However, some plant foods contain less than perfect amounts of one or more amino acids – they do not lack them altogether, they simply contain less than the ideal amount. Because of that, it was suggested that we should always combine certain plant foods to ensure the optimal amino acid intake at every meal. This theory has long been rebutted – science has proven that protein combining is absolutely unnecessary, provided you eat a varied diet with enough calories and not just one plant all day every day (1, 5).
Meat contains all the essential amino acids in sufficient amounts, which is why some people believe it’s a better protein source but it certainly isn’t good for your health. Excess animal protein has been linked to some cancers, heart disease, osteoporosis and kidney damage – more on this below.
How much protein do we need?
An average person needs 0.8 gram of protein daily per kilogram of bodyweight (or 0.36 gram per pound). So for example if you weigh 70 kg/ 155 lb, you need around 56 grams of protein a day. If you’re building muscle, do challenging physical work or train hard, you’ll need to increase your protein intake up to 1.4-2 g per kg of body weight daily.
It’s so easy to get enough protein on a plant-based diet that protein deficiency is virtually unheard of in developed countries. In fact, most of us get too much protein – that’s how easy it is.
Excellent sources of protein include soya products (edamame beans, tofu, tempeh, soya milk, soy yogurt), black beans, kidney beans, baked beans, lentils, chickpeas, whole grains and products made from them (brown rice, whole wheat pasta, wholemeal bread, oats, quinoa, buckwheat), nuts and seeds of all types. Plant protein powders may also be useful if you’re busy, prefer liquid meals or want to increase protein content of your meals.
Protein package deal
Foods are not just single ingredient items. Protein-rich foods also contain many other nutrients, other compounds and sometimes toxins, too. That’s one of the reasons why plant and animal protein have such different health effects.
Plant protein usually comes together with fibre, antioxidants, complex carbs, beneficial phytochemicals, vitamins and minerals – a health-promoting package. Animal protein usually comes with some vitamins and minerals, is devoid of fibre, but has plenty of unhealthy saturated fats and a diverse mixture of toxic and cancer-causing compounds (6, 7).
Another reason why plant protein is beneficial for us whilst animal protein can cause harm is the different amino acid proportions. Animal protein containing more sulphur amino acids than plant protein – these form sulphuric acid in the body which is very strong. Your body neutralises it by using calcium readily available in the blood or muscles but if there is a consistent supply of animal protein, there’s too much acid in the body and some calcium may be released from the bones (8).
Animal protein also sends the kidneys into overdrive for hours after ingestion – their blood vessels dilate and let some protein molecules through into the urine (9). The kidneys should not let any protein through so protein in the urine is a sign of abnormal kidney response. Plant protein doesn’t trigger this response and has been recommended over animal protein for people at risk of or suffering from kidney disease for many years (10, 11).
Lastly, there’s one more reason why animal protein is bad news for our health - it contains high amounts of phosphorus and these can, over time, lead to kidney and bone mineral disorders (12). Plants also contain phosphorus but it’s bound in a hard-to-digest form so much less of it is absorbed by the body – in a nutshell there’s no risk of excessive intakes.
Protein, Kidneys and Bone Health
Kidneys are our trustworthy filtration system, removing waste products from the blood and excreting them in urine. If we eat foods that don’t put an extra strain on them, they work well. However, animal protein makes them work hard and it may result in a reduced filtration capacity and some molecules leaking through – not ideal. If we overload them daily, there’s a higher chance we develop kidney disease. Data from a study spanning over 23 years suggest that animal protein from red and processed meat in particular seriously increases the risk of kidney disease later in life (13). The same study also revealed that plant protein from pulses and nuts has the opposite effect – it lowers the risk and seems to have a kidney-protective effect. And a recent review agrees, plant-based diets significantly lower the risk of kidney disease and can even halt the degree of damage in people with compromised kidney health (14, 11).
The higher volumes of acid resulting from animal protein also stress the kidneys. On the other hand, plant protein producing much less acid is not only gentler on the kidneys - it also helps us not to waste calcium to neutralise large amounts of acid, which is important for healthy bones (15, 16, 11).
Several studies highlighted that it’s because plant protein comes with a number of other nutrients that it has such a beneficial effect on our kidneys and bones (17,18, 19, 20).
Plant protein is also great for the heart. If you swap plant for animal protein, it markedly lowers your risk of heart disease (21). It’s not only the effect of the protein but the whole plant foods that support a healthy heart and circulation. Substituting plant protein for animal protein decreases cholesterol and other fats in your blood and helps to keep your blood vessels healthy (22).
And there’s yet another reason why animal protein is bad news – insulin-like growth factor 1 (IGF-1). It’s a growth hormone naturally produced by your liver, vital to childhood growth and stimulating cell growth and reproduction in adults. However, IGF-1 also promotes cancer cell growth and that’s why increased IGF-1 levels are dangerous (23). Scientists warn that whey proteins from dairy products cause a rise in insulin, IGF-1 and growth hormone levels in the human body (24). The association between IGF-1 and cancer is the strongest for prostate cancer (25) and there is also substantial evidence for the same mechanism and breast cancer (26).
Plant protein doesn’t stimulate these changes and vegans have been found to have significantly lower levels of IGF-1 than meat-eaters (27, 28, 29).
We have billions of bacteria in our guts. They help us process food and our diet determines which bacteria species thrive and which do not. These bacteria are also called gut microbiome and they have a huge influence on our immunity, gut health, inflammation and energy levels. Some are good and beneficial, others not so much and can even produce toxic by-products.
Animal products rich in protein and fat promote the ‘bad’ bacteria that release toxins into our bloodstream. Some of these bacteria use a meat compound - carnitine - as an energy source, and produce trimethylamine-N-oxide (TMAO) as a waste product. TMAO is a dangerous substance that stimulates the build-up of cholesterol plaques in your blood vessels (30). It means a regular meat intake increases your risk of heart disease through yet another mechanism.
Plant wholefoods, rich in plant protein, fibre and complex carbohydrates feed the good bacteria that have a positive effect on our health (31). That’s why vegan diets keep your gut wall strong and healthy, lead to lower levels of body inflammation and a stronger immune system (32, 33, 34).
A Protein World of Difference
The health consequences of consuming animal or plant protein cannot be more different. Whilst plant protein offers a vast array of benefits, animal protein harms our health.
A comprehensive study spanning over two decades found that animal protein increases the risk of premature death by up to 23 percent (35). Do we need another reason to switch to a wholefood plant-based diet for good?
1 Marsh KA, Munn EA, Baines SK. Protein and vegetarian diets. Med J Aust. 2013;199(S4):S7‐S10.
2 Clarys P, Deliens T, Huybrechts I, et al. Comparison of nutritional quality of the vegan, vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diet. Nutrients. 2014;6(3):1318‐1332.
3 Karlsen MC, Rogers G, Miki A, et al. Theoretical Food and Nutrient Composition of Whole-Food Plant-Based and Vegan Diets Compared to Current Dietary Recommendations. Nutrients. 2019;11(3):625.
4 Mariotti F, Gardner CD. Dietary Protein and Amino Acids in Vegetarian Diets-A Review. Nutrients. 2019;11(11):2661.
5 Hever J, Cronise RJ. Plant-based nutrition for healthcare professionals: implementing diet as a primary modality in the prevention and treatment of chronic disease. J Geriatr Cardiol. 2017;14(5):355‐368.
6 Abid Z, Cross AJ, Sinha R. Meat, dairy, and cancer. Am J Clin Nutr. 2014;100 Suppl 1(1):386S‐93S.
7 Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association [published correction appears in Circulation. 2017 Sep 5;136(10 ):e195]. Circulation. 2017;136(3):e1‐e23.
8 Rodrigues Neto Angéloco L, Arces de Souza GC, Almeida Romão E, Garcia Chiarello P. Alkaline Diet and Metabolic Acidosis: Practical Approaches to the Nutritional Management of Chronic Kidney Disease. J Ren Nutr. 2018;28(3):215‐220.
9 Kontessis P, Jones S, Dodds R, et al. Renal, metabolic and hormonal responses to ingestion of animal and vegetable proteins. Kidney Int. 1990;38(1):136‐144.
10 Moorthi RN, Vorland CJ, Hill Gallant KM. Diet and Diabetic Kidney Disease: Plant Versus Animal Protein. Curr Diab Rep. 2017;17(3):15.
11 Rose SD, Strombom SJ. A Plant-Based Diet Prevents and Treats Chronic Kidney Disease. JOJ Urology & Nephrology. 2019;6(3).
12 D'Alessandro C, Piccoli GB, Cupisti A. The "phosphorus pyramid": a visual tool for dietary phosphate management in dialysis and CKD patients. BMC Nephrol. 2015;16:9.
13 Haring B, Selvin E, Liang M, et al. Dietary Protein Sources and Risk for Incident Chronic Kidney Disease: Results From the Atherosclerosis Risk in Communities (ARIC) Study. J Ren Nutr. 2017;27(4):233‐242.
14 Kim H, Caulfield LE, Garcia-Larsen V, et al. Plant-Based Diets and Incident CKD and Kidney Function. Clin J Am Soc Nephrol. 2019;14(5):682‐691.
15 Knurick JR, Johnston CS, Wherry SJ, Aguayo I. Comparison of correlates of bone mineral density in individuals adhering to lacto-ovo, vegan, or omnivore diets: a cross-sectional investigation. Nutrients. 2015;7(5):3416‐3426.
16 Burckhardt P. The role of low acid load in vegetarian diet on bone health: a narrative review. Swiss Med Wkly. 2016;146:w14277.
17 Dai Z, Butler LM, van Dam RM, Ang LW, Yuan JM, Koh WP. Adherence to a vegetable-fruit-soy dietary pattern or the Alternative Healthy Eating Index is associated with lower hip fracture risk among Singapore Chinese. J Nutr. 2014;144(4):511‐518.
18 Sahni S, Mangano KM, McLean RR, Hannan MT, Kiel DP. Dietary Approaches for Bone Health: Lessons from the Framingham Osteoporosis Study. Curr Osteoporos Rep. 2015;13(4):245‐255.
19 Gluba-Brzózka A, Franczyk B, Rysz J. Vegetarian Diet in Chronic Kidney Disease-A Friend or Foe. Nutrients. 2017;9(4):374.
20 Kalantar-Zadeh K, Moore LW. Does Kidney Longevity Mean Healthy Vegan Food and Less Meat or Is Any Low-Protein Diet Good Enough?. J Ren Nutr. 2019;29(2):79‐81.
21 Richter CK, Skulas-Ray AC, Champagne CM, Kris-Etherton PM. Plant protein and animal proteins: do they differentially affect cardiovascular disease risk?. Adv Nutr. 2015;6(6):712‐728.
22 Li SS, Blanco Mejia S, Lytvyn L, et al. Effect of Plant Protein on Blood Lipids: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Am Heart Assoc. 2017;6(12):e006659.
23 Jenkins PJ, Mukherjee A, Shalet SM. Does growth hormone cause cancer?. Clin Endocrinol (Oxf). 2006;64(2):115‐121.
24 Melnik BC. Evidence for acne-promoting effects of milk and other insulinotropic dairy products. Nestle Nutr Workshop Ser Pediatr Program. 2011;67:131‐145.
25 Travis RC, Appleby PN, Martin RM, et al. A Meta-analysis of Individual Participant Data Reveals an Association between Circulating Levels of IGF-I and Prostate Cancer Risk. Cancer Res. 2016;76(8):2288‐2300.
26 Bradbury KE, Balkwill A, Tipper SJ, et al. The association of plasma IGF-I with dietary, lifestyle, anthropometric, and early life factors in postmenopausal women. Growth Horm IGF Res. 2015;25(2):90‐95.
27 Allen NE, Appleby PN, Davey GK, Key TJ. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Br J Cancer. 2000;83(1):95‐97.
28 Allen NE, Appleby PN, Davey GK, Kaaks R, Rinaldi S, Key TJ. The associations of diet with serum insulin-like growth factor I and its main binding proteins in 292 women meat-eaters, vegetarians, and vegans. Cancer Epidemiol Biomarkers Prev. 2002;11(11):1441‐1448.
29 McCarty MF. GCN2 and FGF21 are likely mediators of the protection from cancer, autoimmunity, obesity, and diabetes afforded by vegan diets. Med Hypotheses. 2014;83(3):365‐371.
30 Koeth RA, Lam-Galvez BR, Kirsop J, et al. l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans. J Clin Invest. 2019;129(1):373‐387.
31 Tomova A, Bukovsky I, Rembert E, et al. The Effects of Vegetarian and Vegan Diets on Gut Microbiota. Front Nutr. 2019;6:47.
32 Glick-Bauer M, Yeh MC. The health advantage of a vegan diet: exploring the gut microbiota connection. Nutrients. 2014;6(11):4822‐4838.
33 Craddock JC, Neale EP, Peoples GE, Probst YC. Vegetarian-Based Dietary Patterns and their Relation with Inflammatory and Immune Biomarkers: A Systematic Review and Meta-Analysis. Adv Nutr. 2019;10(3):433‐451.
34 Rinninella E, Cintoni M, Raoul P, et al. Food Components and Dietary Habits: Keys for a Healthy Gut Microbiota Composition. Nutrients. 2019;11(10):2393.
35 Virtanen HEK, Voutilainen S, Koskinen TT, et al. Dietary proteins and protein sources and risk of death: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2019;109(5):1462‐1471.