How does your diet link to cancer?

When it comes to dietary advice, knowing who to trust is important as an internet search about diet and cancer can leave you feeling confused and possibly even scared. For this year’s Breast Cancer awareness month, Jo Cunningham, an oncology and gut-specialist dietitian from The Gut Health Clinic, takes a closer look at the links between diet and cancer, bringing you evidence-based advice as well as answering some common questions.


Dietitians are qualified and regulated nutrition experts who use the most up-to-date scientific research which they translate into practical guidance to enable people to make appropriate food and lifestyle changes. When it comes to cancer advice, they debunk myths surrounding cancer and diet, help manage common treatment side effects, as well as optimise nutritional status to support the immune system through treatment and beyond.

Considering the evidence-base, the World Cancer Research Fund (WCRF) has an ongoing programme that analyses global scientific research on how diet, nutrition and physical activity can affect cancer risk and survival. The research entered into this “Continuous Update Project” database is systematically reviewed, evaluated, and interpreted by an independent panel of world-renowned experts meaning that the WCRF recommendations are trustworthy. When considering breast cancer specifically, note that the evidence base consists of more than 12 million women and over 260,000 cases of breast cancer.

The following infographic summarises the WCRF cancer prevention recommendations:

Should I have a different diet depending on whether I do or don’t have cancer?

The advice for what to eat whilst living with cancer is, broadly speaking, the same as what we should be eating to minimise the risk of developing cancer. That’s a healthy balanced diet containing minimal amounts of added sugar and processed foods, and plenty of wholegrains, vegetables, fruits, and legumes.

We now know from research that by aiming for a varied, plant-based diet it supports a healthy gut microbiome (the trillions of microbes living inside our gut) which may have a protective role in the development of some cancers.  This doesn’t mean you have to give up meat, fish, and other animal products completely if you enjoy them; it’s all about the protein-fibre ratio which means animal proteins shouldn’t make up the majority of the diet, especially not the processed meats which contain known carcinogenic (cancer-forming) properties.

To feed your gut microbes, we recommend aiming for 30+ different types of plants across the course of each week. Plant foods contain chemicals called polyphenols that have been linked with not only cancer prevention but also better heart and mental health. Many plants also contain prebiotics (not to be mistaken for probiotics which are the live bacteria found in food or supplements) which mean they feed specific beneficial microbes within the gut for a proven health benefit such as blood sugar control, appetite regulation, and immunity.

Note that whilst we support someone embarking on a fully vegan diet, it’s worth noting that there’s a limited number of studies examining the impact of a vegan diet on cancer risk. There are some important nutritional considerations for someone who would like to become vegan, so it does need some careful planning. We can help with this at The Gut Health Clinic.

What are the recommended daily intakes?

To help us achieve the 30+ plants each week as a rough guide, each day we’re aiming for:

  • 2-3 pieces of fruit (spread the intake out across the day)
  • 5-7 portions of vegetables/salad (e.g., 3 and lunch and 4 at dinner)
  • 3 portions of wholegrains (wholewheat pasta, quinoa, buckwheat, oats)
  • 1-2 portions of nuts (or nut butters)/seeds/legumes
  • Herbs & spices

We should also include some protein-rich foods with each meal to promote healthy muscle growth and repair. Aim to include fish, particularly oily fish, 2 times per week; limit red meat intake to 1-2 times per week and avoid processed meats where possible. Plant-based sources of protein include beans, lentils, chickpeas, tofu, and nuts.

We shouldn’t forget our fats which are essential for the structure of our cells as well as to aid absorption of some vitamins. Sources can include nuts and seeds, oily fish, extra virgin olive oil, avocado, and olives. Limit consumption of animal fats like butter, visible fat on meat, and large portions of cheese. For cooking, use a small amount of extra virgin olive oil, rapeseed oil, butter, or coconut oil. When oil starts to smoke its chemical structure changes which can release harmful chemicals called free radicals into your food. So, use nut and other oils as a garnish rather than cooking with them as they have a much lower smoking point.

Aim to drink at least 2 litres of fluid per day ensuring to sip fluid during mealtimes. Limit fizzy drinks and sugary squashes and cordials, and instead try flavouring water with things such as lemon, lime, mint leaves, and fruit. Herbal teas can also be enjoyed hot or cold.

Does sugar feed or cause cancer?

On a molecular level, sugar comes in different forms, the simplest of which is the molecule called glucose. All the cells in our body, both healthy and cancer cells, use glucose as their main energy source which is why the common misconception arises that we should cut out all sugar to starve cancer. Unfortunately, it really isn’t that simple because even if you were to remove all sources of sugar in the diet it wouldn’t stop cancer growing. Furthermore, our bodies are great at adapting and without glucose from dietary sources it will start using protein and fat to produce glucose, which can lead to the breakdown of protein stores in the body contributing to muscle loss and malnutrition.

Sugar is found within wonderfully healthy fibre-filled foods such as wholegrains, fruits, vegetables, nuts, and within dairy. It is also added to foods such as cakes, sweets, biscuits, and sweetened beverages. If we were to exclude all sugar, whilst we don’t need the added sugars from a nutritional perspective, we’d be missing all those plant-based sources, which could lead to constipation, low energy, nutritional deficiencies, weight loss and perhaps even being too unwell to receive cancer treatment.

Whilst it’s unlikely that sugar directly causes cancer (there’s no evidence to date to support this) we do know that there’s an indirect link between sugar and cancer. A diet high in foods containing added sugars can contribute to inflammation as well as excess calorie intake which over time may lead to weight gain and excess body fat which is a risk factor for many types of cancers. These types of diets are often also lower in plant-based foods and fibre too.

In conclusion: whilst it’s not necessary to avoid sugar completely especially if it is from within nutrient-dense sources like our plant foods, reducing added sugars in the diet will help not only with inflammation but also with maintaining a healthy weight which has health benefits.

Is dairy safe to consume?

It’s a common dietary misconception that dairy should be avoided. When it comes to breast cancer, the verdict is that there is NO clear link between dairy containing diets and cancer risk, or that it promotes cancer growth. In fact, there’s some evidence to support including dairy in the diet as it may have a protective role and reduce the risk of breast cancer.

If you’re wondering about the hormones found within dairy, the first thing to say is that in the UK growth hormones are not used for livestock. Secondly, the hormones found naturally within dairy milk is small compared to the amount organically produced in the human body. There’s no strong evidence to suggest that hormones in milk could go on to cause cancer.

In conclusion: dairy may have a protective role when it comes to breast cancer risk so can be included in the diet if you wish. If you prefer to be dairy free, it’s always best to discuss this with a dietitian to ensure adequate calcium and iodine intake to support bone health, metabolism, nerve impulses, blood clotting and digestion. We can help with this at The Gut Health Clinic.

Can I drink alcohol?

The WCRF recommends that for cancer prevention, it’s best not to drink alcohol. We know that when alcohol is consumed it converts into a substance called acetaldehyde which can disrupt DNA synthesis and repair which may contribute to a “carcinogenic cascade”. The current evidence shows that in general, the more alcohol that is consumed, the higher the risk of many cancers, including breast cancer. It’s worth noting that those who drink large amounts of alcohol may also have diets lacking in essential nutrients and those protective plant-based chemicals mentioned earlier.

The UK recommendations are not to drink more than 14 units a week on a regular basis, spreading your drinking over 3 or more days, and aiming for several drink-free days each week.

In conclusion: even though red wine does contain some polyphenols which our gut bugs love, we suggest that you limit the booze where possible. Consider having a non-alcoholic drink like a mocktail or water (or kombucha for some gut-loving benefits!) in between alcoholic beverages.  If you are having an alcoholic drink, perhaps add a slice of fruit to it for something for the microbes (fruit and gin goes nicely together so we’ve heard!). Finally, if you are enjoying a tipple, be sure to eat a good meal beforehand and aim for a diet rich in plants to nourish your gut microbes because keeping them happy can help keep you healthy!

Get in touch

If you’d like to discuss any aspect of cancer and the diet with one of the team at The Gut Health Clinic, we’d be happy to see you either at OneWelbeck or in our online consultations. You can find our contact details here

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Written by Jo Cunningham

Written by Jo Cunningham, oncology and gut-specialist dietitian from The Gut Health Clinic.