Plant-based diet and cancer
by Dr Laura Freeman
Genetics are responsible only for less than 10% of cancer cases
Many people still believe that cancer is genetic and that it’s an inevitable part of life. Of course, this is true for a minority of cancers, which are caused by the genes we may have inherited from our parents, but only in less than 10% of cases. Cancer cells do have abnormalities in their genes and chromosomes which gives them the characteristics we associate with cancer, but these genetic defects are usually acquired during life for a variety of reasons. Many of these reasons relate to our dietary, lifestyle and environmental exposures.
4 out of 10 cancers could be prevented by healthy diet and lifestyle
We are all very familiar with the fact that smoking tobacco causes cancer. Yet I suspect most people are less familiar with the fact that diet and other lifestyle factors are also implicated in generating cancer cells. In fact, 4 out of 10 cancers could be prevented by adopting healthy lifestyle habits (1). Potential cancer cells are constantly being generated in our body. Most of the time our body’s defences can deal with them by either removing them or just allowing them to stay dormant and harmless. However, under the right conditions, these cells can start to divide and multiply, eventually giving rise to cancer that causes symptoms.
The main preventable risk factors for cancer in addition to tobacco smoking are being overweight, insufficient physical activity, poor diet, alcohol consumption and unsafe exposure to the sun (skin cancer). Many are surprised to learn specifically about the impact of diet on cancer risk. Not only do diet choices impact our weight, but certain foods are known to promote the growth of cancer, whereas others act to prevent it.
Fruits and vegetables prevent cancer and support the immune system
Food that’s have been shown to prevent cancer are fruits and vegetables, whole grains, beans, nuts and seeds. That sounds pretty much like a healthy vegan diet! The reason being is that these foods are packed with anti-cancer compounds, including antioxidants and anti-inflammatory compounds. They are rich in fibre which promotes a healthy gut microbiome and is key to maintaining a healthy immune system and warding off cancer cells (2). In addition, these healthy plant foods reduce insulin resistance and keep hormone levels in check, including oestrogen and insulin-like growth factor, important for preventing cancers from growing (3). Although I don’t worry too much about which fruits and vegetables I eat, instead of emphasising variety, certain vegetables are particularly high in anti-cancer compounds. These include mushrooms, cruciferous vegetables (broccoli, cabbage, Brussel sprouts etc) and onions and garlic (4–6). In addition, herbs and spices have the highest concentration of antioxidants helping to prevent the formation of precancerous cells (7).
Processed meat is carcinogen
In contrast, processed red meat has been classified by the World Health Organisation as a group 1 carcinogen, which means its consumption is a direct cause of cancer. This is mainly in relation to bowel cancer and in the UK 13% of bowel cancers, over 5000 cases per year, are thought to be directly caused by eating processed red meat. Unprocessed red meat is a Group 2A carcinogen, which means its consumption probably causes cancer. In addition to bowel cancer, processed and red meat increases the risk of breast, pancreatic, nasopharyngeal, oesophagus and stomach cancers. This is because meat does not contain any of the anti-cancer compounds found in plant foods, has no fibre and instead contains compounds that can directly damage the DNA of cells (8).
What about a vegan or plant-based diet? Can becoming vegan help prevent cancer? A large analysis from 2017 bringing together information from a number of different studies on vegan diet and health, showed that those consuming a vegan diet had a 15% reduction in the risk of developing cancer (9). Similarly, a study from 2018 that examined the impact of eating a healthy plant-based diet showed a 15% reduction in the risk of developing cancer (10). However, it is worth noting that there is some concern that processed foods, be they vegan or not, may actually increase the risk of certain cancers (11). So, it’s always best to minimise these foods in the diet.
A common question I get asked is whether it’s best to only eat organic fruits and vegetables to avoid exposure to pesticides and herbicides. In the ideal world, we would want all our food to be free of chemicals, but this is not realistic in our current food system. What’s clear is that is always best to eat lots of fruits and vegetables and a good variety as the benefits outweigh any potential risk of exposure to chemicals (12). The good news is that vegans have lower exposure to environmental chemicals, including persistent organic pollutants, as these compounds concentrate higher up the food chain in the fat of animals. So overall a vegan diet goes a long way to reducing your exposure to these chemicals(13).
Don’t forget there are a number of other healthy habits that will significantly reduce your risk of developing cancer. These include regular physical activity, at least 150 minutes per week, avoiding alcohol and tobacco smoking and maintaining a healthy weight.
Sadly, we can’t prevent every single case of cancer and even people who have done the ‘right thing’ all their lives, can of course still develop cancer. The focus of this article is really about empowering you to make healthy choices and stack the odds in your favour. These same healthy lifestyle habits, including a plant-based diet, are also associated with the lowest risk of heart disease, type 2 diabetes and dementia, therefore giving you the best chance of a long and healthy life.
- Rock CL, Thomson C, Gansler T, Gapstur SM, McCullough ML, Patel A V., et al. American Cancer Society guideline for diet and physical activity for cancer prevention. CA Cancer J Clin. 2020;
- McQuade JL, Daniel CR, Helmink BA, Wargo JA. Modulating the microbiome to improve therapeutic response in cancer. The Lancet Oncology. 2019.
- Levine ME, Suarez JA, Brandhorst S, Balasubramanian P, Cheng CW, Madia F, et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metab. 2014;
- Ba DM, Ssentongo P, Beelman RB, Muscat J, Gao X, Richie JP. Higher Mushroom Consumption Is Associated with Lower Risk of Cancer: A Systematic Review and Meta-Analysis of Observational Studies. Adv Nutr. 2021;
- Royston KJ, Tollefsbol TO. The Epigenetic Impact of Cruciferous Vegetables on Cancer Prevention. Current Pharmacology Reports. 2015.
- Wan Q, Li N, Du L, Zhao R, Yi M, Xu Q, et al. Allium vegetable consumption and health: An umbrella review of meta-analyses of multiple health outcomes. Food Science and Nutrition. 2019.
- Carlsen MH, Halvorsen BL, Holte K, Bøhn SK, Dragland S, Sampson L, et al. The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutr J. 2010;
- Wolk A. Potential health hazards of eating red meat. Journal of Internal Medicine. 2017.
- Dinu M, Abbate R, Gensini GF, Casini A, Sofi F. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Crit Rev Food Sci Nutr. 2017;
- Kane-Diallo A, Srour B, Sellem L, Deschasaux M, Latino-Martel P, Hercberg S, et al. Association between a pro-plant-based dietary score and cancer risk in the prospective NutriNet-santé cohort. Int J Cancer. 2018;
- Fiolet T, Srour B, Sellem L, Kesse-Guyot E, Allès B, Méjean C, et al. Consumption of ultra-processed foods and cancer risk: Results from NutriNet-Santé prospective cohort. BMJ. 2018;
- Aune D, Giovannucci E, Boffetta P, Fadnes LT, Keum N, Norat T, et al.Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality—a systematic review and dose-response meta-analysis of prospective studies. Int J Epidemiol [Internet]. 2017 Jun 1;46(3):1029–56. Available from: https://academic.oup.com/ije/article/46/3/1029/303947713. Dervilly-Pinel G, Guérin T, Minvielle B, Travel A, Normand J, Bourin M,et al. Micropollutants and chemical residues in organic and conventional meat. Food Chem. 2017;