Breast cancer and food: what the science actually says

A breast cancer diagnosis can make you more interested in what you eat. But when you start looking, much of the “advice” is confusing or frightening, and in my clinic I meet women who have cut out huge lists of foods based on information they’ve come across online. 

Social media especially can be a misleading place where personal stories are presented as proof, often by people with no relevant training. The title “nutritionist” alone isn’t protected, so anyone can use it, whereas “dietitian” is legally protected and requires years of regulated training. So always look for a registered dietitian, or a nutritionist who is registered on the Association for Nutrition’s register, with relevant experience in the area you want support with.

Here’s what I get asked about most often by my breast cancer patients, and what the evidence says is worth focusing on.

The five foods I am asked about most

Sugar. Sugar does not "feed" cancer in the way social media suggests. Every cell in your body uses glucose for energy, and your body makes its own even if you eat none, so you do not need to remove fruits and carbohydrates. A diet high in sugary foods and drinks can provide excess calories which can lead to weight gain - and obesity is associated with cancer. So we DO need to reduce those added-sugar foods and keep them as occasional extras, but not for the "sugar-feeding-cancer" reason you’re thinking. 

Dairy. There is no good evidence that dairy causes breast cancer or makes it come back. Milk, yoghurt and cheese provide protein, calcium and iodine, and calcium matters as many breast cancer treatments affect your bones. If you prefer plant-based alternatives, that’s absolutely fine - choose ones with added vitamins and minerals.

Soy. Soy contains plant oestrogens, and these have long been feared. However, large studies following women after breast cancer have found soy foods to be safe, if not beneficial when considering recurrence risk. Furthermore, soy may help reduce hot flushes. Tofu, edamame, soy milk and soy yoghurt are great plant proteins to include in the diet. Concentrated soy isoflavone supplements are a different matter, and I advise avoiding them.

Meat. The evidence linking red and processed meat to cancer is strongest for bowel cancer. A sensible amount for red meat is around two portions a week. Processed meats like bacon, ham, gammon and deli meats are best avoided for cancer prevention according to WCRF. Aim to rotate your protein sources to have some meat, some fish, and some plant proteins for balance across the week. 

Alcohol. This is the one with the strongest evidence. Alcohol raises the risk of breast cancer and it may also impact the risk of recurrence. No level is completely safe. I am not saying you can never have a drink again, I’m just giving you the truth for you to choose what to do with it. 

A word of caution on supplements

More is not better and dietary supplements aren’t always safe. 

High-dose antioxidants such as vitamins A, C and E may interfere with chemotherapy and radiotherapy. Herbal supplements can also interact with medications. 

Vitamin D is often a sensible exception, and sometimes omega-3 or others where there is a diagnosed deficiency, but tell your oncology team about everything you take and check before starting anything new.

What to focus on instead

No single food causes or cures breast cancer. What matters is your overall pattern of eating, over months and years. The pattern with the most support is a Mediterranean-style diet. 

In a study I co-authored in collaboration with Field Doctor and Perci Health, 46 women who had been through breast cancer treatment completed a 12-week programme of Mediterranean-style meals and online education. We saw improvements in BMI and hot flushes, as well as confidence in food choices. It was a small study with no comparison group, but the results were encouraging and in line with the wider evidence. 

In practice, that means aiming for a diet with:

• Plenty of vegetables, fruit, wholegrains, beans and lentils
• Enough protein at each meal
• Good amounts of omega-3 (oily fish at least once a week, or including walnuts, chia seeds and flax seeds)
• Extra virgin olive oil
• Less alcohol

Final thoughts

Eating enough matters more than eating perfectly, and after breast cancer treatment, food should be enjoyed and shared with people you love, without a list of restrictions. 

Everyone's situation is different, and what's right for you depends on your diagnosis, treatment, and health history. Putting the evidence into practice is much easier with a plan built around you. If you feel confused or worried, ask your medical team to see a registered dietitian who specialises in oncology or you can contact my team to book your support today.

This isn’t a substitute for advice from your own team.