Key takeaways
- Evidence is clear that a plant-based diet is best for cancer prevention, however this doesn’t mean you can’t eat animal foods
- A plant-based diet and healthy gut microbiome have been shown to protect against certain types of cancer, as well as benefit overall health
- Aim to eat a wide variety of plant-based foods across the week, including vegetables, fruits, wholegrains, nuts and legumes
- If you want to go vegan, it’s a good idea to talk to a dietitian, to ensure you’re getting all the nutrients you need
There’s so much information available about diet and cancer. Unfortunately much of the ‘advice’ available on the internet is not factually correct or supported by robust scientific evidence. In this guide, Perci dietitian Jo Cunningham explains why, if you’re interested in cancer prevention, a plant-based diet is best, but this doesn’t necessarily mean going vegan. She also explains the role of the gut microbiome and how to support it with what you eat.
Is a plant-based diet effective for cancer prevention?
According to the evidence, a plant-based diet, containing minimal amounts of added sugar and processed foods, is best for cancer prevention. The same applies for when living with cancer. It might not sound glamorous (especially when compared to headlines promoting restrictive diets or cleanses), but it really does make scientific sense.
A landmark study by the American Gut Project in 2018 found that people who ate 30 or more plants per week had more diverse gut bacteria compared to those who had 10 or fewer plants per week. Robust evidence shows that the greater our gut microbe diversity, the better our health we will be.
It might not sound glamorous but a plant-based diet really does make scientific sense
Jo Cunningham, Dietitian
What does our gut bacteria do for us?
When you have a varied, plant-based diet, you’re feeding the trillions of microbes living in your large intestine (also known as the gut microbiome). This beneficial bacteria enables us to digest our food efficiently as well as absorb vitamins and minerals effectively, contributing to improved energy and performance. It also plays a role in hormone regulation and neurotransmitter production, which are the chemicals that control our mood and contribute to looking after our mental health.
Something else found in plants are prebiotics. These are not to be mistaken for probiotics (which are the live bacteria found within supplements or fortified foods). Prebiotics are fibres found within plants that feed the microbes. They have a scientifically proven benefit to our health, for example, improved blood sugar control, appetite regulation and immunity.
When thinking about what to eat, remember to aim for a wide variety of plant-based foods, with plenty of different colours, textures and flavours. Without variety, our microbes may not get the fuel they need, and die off, which can impact our digestion and overall health. Nourishing your microbes will, in turn, benefit your overall health.
How does our microbiome relate to cancer?
In terms of cancer prevention, these clever microbes have a protective role in the development of some cancers. They produce beneficial compounds known as short-chain fatty acids, which have been shown to reduce the risk of colon cancer. Also, within many plant foods are chemicals called polyphenols, which have been associated with cancer protection. Recent studies have found that a diverse gut microbiome may affect how a person responds to cancer treatment – in terms of side-effects – as well as treatment success.
What does a plant-based diet look like?
As a very rough guide, each day aim for:
- 2–3 pieces of fruit (spread the intake out across the day)
- 5–7 types of vegetables or salad (e.g., 3 at lunch and 4 at dinner)
- 3 types of wholegrains (e.g., wholewheat pasta, quinoa, buckwheat, oats)
- 1–2 portions of nuts (or nut butters) and seeds
- 1–2 types of legumes (beans, chickpeas and lentils)
- Herbs and spices
Does a plant-based diet mean a vegan diet?
A plant-based diet does not necessarily mean a vegan diet. You can still eat meat, fish and other animal products if you enjoy them, and the evidence says it’s safe to do so.
What we’re learning from the research is that it’s the balance of protein to fibre that’s important. When our microbes ferment upon contact with protein in our gut, they produce compounds called uremic toxins. These cannot be eliminated from the body and build up in the bloodstream where they reach organs including the kidneys and heart. This has been associated with increased mortality in patients with chronic kidney disease. Studies suggest that dietary fibre may counteract the production of those harmful compounds. Essentially, this means that we should be aiming for more plants (fibre) and fewer animal foods in our diet.
If you are eating meat, ideally avoid processed meats, such as ham and sausages, which contain known carcinogenic (cancer-forming) properties. It’s one of the few things I tend to tell members to avoid – the evidence is pretty strong for this recommendation.
If you want to go vegan that’s okay, however, there are some key nutrients that need to be considered when removing all animal products from your diet. If you’re considering becoming vegan, it’s a good idea to talk to a dietitian to make sure you’re getting all the nutrients you need.
What else should we be including in our diet?
Protein
Include a protein source with each meal to promote healthy muscle growth and repair. This is especially important for someone who is going through cancer treatment, during which muscle mass is crucial. Aim to eat oily fish twice a week and limit red meat to one or two times per week (avoiding those processed meats). If you don’t eat meat or fish, try to include eggs, cheese and/or Greek yoghurt. Sources of plant-based or vegan protein include beans, lentils, chickpeas, tofu and nuts.
Fats
Fats are important as they help to absorb some vitamins. They also make up the surrounding layer of all the cells in our body. Contrary to popular belief, we shouldn’t be avoiding fats. In fact, we should be aiming to include plenty of healthy sources, such as nuts, seeds, oily fish, extra virgin olive oil, avocado and olives. Unless you’re trying to gain weight, try to limit consumption of animal fats like butter, visible fat on meat and large portions of cheese.
Contrary to popular belief, we shouldn’t be avoiding fats. In fact, we should be aiming to include plenty of healthy sources.
Jo Cunningham, Dietitian
For cooking, use an extra virgin olive oil, rapeseed oil, butter, or coconut oil. Something to bear in mind is that if your oil is smoking, then its chemical structure changes and can be more harmful when eaten. Save those nut, seed or other oil types as a garnish rather than cooking with them, as they tend to have a much lower smoking point.
Fluids
Aim to drink at least two litres of fluid per day, and sip fluid during mealtimes to help that fibre go through your digestive tract. Where possible, limit fizzy drinks, squashes and cordials, which can be high in sugar or artificial sweeteners. Instead, try flavouring water with lemon, orange or mint leaves.
It’s never too late to introduce more plants into your diet. Whether you are interested in cancer prevention, or are living with or beyond cancer, a dietitian can help you to make small or substantial changes to your diet to optimise your health. Read more about Perci dietitian Jo Cunningham and book an appointment.
While we have ensured that every article is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. If you have any questions or concerns, please talk to one of our healthcare professionals or your primary healthcare team.
References
McDonald D, Hyde E, Debelius JW, et al., ‘American Gut: an Open Platform for Citizen Science Microbiome Research’, mSystems 20183(3):e00031-18, May 2018, https://doi.org/10.1128/mSystems.00031-18
Rossi M, Johnson DW, Xu H, et al., ‘Dietary protein-fibre ratio associates with circulating levels of indoxyl sulfate and p-cresyl sulfate in chronic kidney disease patients’, Nutr Metab Cardiovasc Dis. 2015;25(9):860-865, https://doi.org/10.1016/j.numecd.2015.03.015
Yu, ZK., Xie, RL., You, R. et al, ‘The role of the bacterial microbiome in the treatment of cancer’, BMC Cancer 21, 934 (2021), https://doi.org/10.1186/s12885-021-08664-0