Before my breast cancer diagnosis, my diet was… if not terrible, pretty close to it. I was a trainee breast surgeon constantly on the go, either working long hours, fuelled by Red Bull, out drinking with colleagues or (occasionally) sleeping.
I mostly ate beige foods: bowls of cereal, chips, the odd bagel or ready meal. If it could be eaten on the go, in a few minutes, all the better. Fresh fruit and veg – and cooking, for that matter – rarely entered the picture.
Getting married to my husband Dermot meant my diet did improve, but whenever he was away, I reverted to my old habits. And in 2015, aged 40, after I learned I had the disease that I’d spent my career treating, that didn’t change.
I’d already cut down on my alcohol intake when I got married, and after my diagnosis I drank even less. But I didn’t really think about anything else. I trusted my medical treatment to do its job.
My left breast was cut away, I had chemo and radiotherapy, and for a while I thought that was it.
But in 2018 the cancer returned, and then again in 2023. After that, I couldn’t ignore the persistent nagging worry I had that diet has a role in cancer prevention and recurrence.
I’m on social media and I read news websites. Like everyone, I’m constantly bombarded with advice about supplements and foods that either cause or miraculously cure cancer if we eat enough of them (often, confusingly, both).
As a doctor, I know at best these claims are often based on the flimsiest of evidence.
Dr O’Riordan believes you can eat the foods you love while reducing your cancer risk
Not long ago I got into a public spat with a pair of high-profile vegan influencers who had told their millions of followers that eating mushrooms could halt breast cancer, when nothing of the sort is true. It turned out the claim was based on a small study on mice in a lab.
Likewise, I’m uncomfortable when the public are scared that certain foods increase cancer risk. Yes, over a lifetime, a diet very high in red and processed meats will make bowel cancer more likely. While this sounds alarming, the actual risk is very small – unless you eat a lot of meat, every day, for several years.
And I hate the idea of cancer patients feeling guilty for eating a bacon sandwich or drinking a can of Coke – or thinking that, because they might have done so in the past, their illness is somehow their own fault.
No one can tell you what caused your cancer, and diet is only a small part of it. There’s just no proof that this is the case. The risk with food isn’t as clear cut as it is with, say, smoking or drinking alcohol.
Yet, food does play a role. What we eat affects our body’s ability to repair, maintain a healthy weight and reduce inflammation – all of which are critical for cancer prevention and recovery. And recent research suggests as many as five in every 100 cancers are related to diet.
So I have begun to look at my own diet – and, more importantly, its shortcomings.
I’ve spent time with colleagues, including Dr Clare Shaw, consultant oncology dietician at the Royal Marsden Hospital in London. I started following cancer scientists on social media who debunk food myths.
And I scoured bona fide resources, such as Cancer Research UK, the World Cancer Research Fund and the American Cancer Society, which all provide evidence-based recommendations that are straightforward and achievable.
It was a lot of work, but it was worth it. And I made changes. Fast forward to now, aged 50, I’d say I’m in the best shape of my life – and I want to share what I have learned.
Although this is mainly aimed at those with a cancer diagnosis, anyone who wants to reduce their risks will also benefit.
Dr O’Riordan before a second operation. She first learned she had breast cancer in 2015, aged 40
1. My cancer-fighting ‘Triple-F’ Rule
Reducing your cancer risks means making healthy food choices. However, this doesn’t mean depriving yourself of joy.
I live by the 80:20 rule, but have made my own modification. In my opinion, food should be:
- Fuel (80 per cent) – nutritious foods that nourish your body
- Fun (20 per cent) – treats such as chocolate or a meal with friends
- F**k It – for moments when only food can soothe your soul.
I know what you’re thinking – that adds up to more than 100 per cent – but bear with me.
There are days when everything goes wrong. I’ll open a bottle of wine, eat a bag of crisps or a whole packet of Hobnobs.
We all have moments when you need a quick fix to feel better. I’ve gone into a downhill spiral in the past, beating myself up over it, but that doesn’t help. Now I call it ‘F**k It’ food.
But unlike when I was younger, I now first ask myself: is there anything else I can do to lift my mood? Phone a friend? Go for a walk? Write an angry email? What emotion am I actually feeling? Nine times out of ten I will still reach for the biscuits, but I’ll have fewer.
One moment of over-indulgence will have no impact on my health. I admit that it’s what I needed at the time and move on. Life happens. This balance keeps me healthy without feeling deprived.
2. Eat a (mainly) plant-based diet…
Following a vegetarian diet significantly reduces the risk of developing cancers of all kinds, according to a large-scale analysis from the University of Oxford.
The same study found that pescatarians – people who eat fish but not meat – and those who consumed meat fewer than five times a week, were also at reduced risk of breast, colon and prostate cancers.
Part of the reason, the researchers suggested, was that veggies tended to be a lower body weight.
Dr O’Riordan in a YouTube video explaining the ways you should check your breasts for cancer
However, fresh fruit and veg also provide essential fibre, a good balance of vitamins, minerals and other nutrients linked to a reduced cancer risk.
For these reasons, the American Institute for Cancer Research recommends that two-thirds of every meal is plant-based. Research has also shown that eating like this is associated with a reduced risk of cancer progression and recurrence, which is particularly important to me.
But it’s something I’ve had to work on, as my bowls of cereal and tuna sandwiches don’t fulfill me. I now have a handful of berries each morning with whatever else I eat, and chop up peppers, carrots and celery to add to lunch. I’ll add grated carrots and beans into tomato-based pasta sauces, boosting the fibre content.
I definitely feel better for it and my bowels are thankful too.
3. …and limit red and processed meat
All of the world’s cancer organisations agree that red meat – beef, pork and lamb – should be limited to three portions, of roughly 85g each, per week, in order to reduce colon cancer risk.
In addition, processed meats such as bacon, sausages and ham should be avoided or eaten sparingly for the same reason.
Do I follow this? I don’t eat a lot of red meat, but I still eat a bacon sandwich a couple of times a month at a great local cafe and I enjoy it. Make them an occasional treat instead of a daily one.
4. Pack in the protein during every meal
Protein is crucial to the body for repair and recovery, especially after surgery or during treatment. It includes lean meats, fish, eggs, beans, tofu, and nuts.
Cancer Research UK suggests halving your bodyweight to find the amount of protein you need in grams per serving.
So a nine-and-a-half stone (60kg) woman should be eating 30g of protein with each meal.
A portion of chickpeas contains about 15g protein and there’s 6g in an egg.
A bowl of porridge has about 14g, while a 100g salmon fillet contains about 20g. A small chicken breast – roughly 150g – provides 36g.
My husband would say I’m fussy (and he’s right) as I don’t like porridge, eggs or cheese (another protein source), so breakfasts are hard.
I now have a chocolate protein shake first thing and it stops me craving biscuits later in the morning. I feel more full and I’ve got more energy when I’m out and about.
What we eat affects our body’s ability to repair, maintain a healthy weight and reduce inflammation – all of which are critical for cancer prevention and recovery, writes Dr O’Riordan
5. Cut back on ultra-processed foods
Ultra-processed foods (UPFs) such as crisps, fizzy drinks, takeaways and ready meals are high in salt, sugar, and unhealthy fats.
Some studies suggest UPFs may increase cancer risk, but the absolute impact is small. Rather than avoiding them entirely, enjoy these foods occasionally.
But, to be honest, I’d find it impossible to live my life without UPFs. Like most people, I don’t have the time, money, patience or energy to cook all my meals from scratch.
I’ve recently subscribed to Hello Fresh, a delivery service which provides meal kits at under £7 per meal. It’s affordable and means I don’t have to think about what to cook every night. And there are times when I’ll get a ready-made curry from the supermarket.
What I do now though is cook extra vegetables to go with it. I swear by packets of frozen mixed veg that you steam in the microwave. Also, now that I eat more during my main meal, I don’t crave crisps and biscuits like I used to.
6. Limit Alcohol Consumption
Alcohol has been directly linked to at least seven cancers, and even just a glass a day, or once or twice a week, increases the risk.
There’s no safe amount. Reducing your intake will lower your risk of getting cancer. If you adopt only one of these bits of advice, follow this one as it will have the most impact.
I know this is easier said than done. I drank a lot at medical school and as a junior doctor, and I have questioned whether that’s why I got breast cancer.
I’ll never know the answer, but if I could turn back time I might make different choices.
There’s not a lot of research to prove whether drinking after cancer can increase the risk of recurrence, but it makes sense to cut down.
I had a couple of hangovers after celebrating the end of my first round of treatment, but they made me feel like I was in the middle of chemo again.
Thanks to my treatment-induced menopause, even a small glass of wine is never worth it because of the torrential night sweats.
My current pills give me tongue ulcers and alter my taste, and that’s why I rarely drink.
You have to decide for yourself what risks you are willing to take and who to believe when it comes to those risks.
In the past couple of years there’s been a huge increase in the number of non-alcoholic beers, wines and spirits available, so we’re no longer limited to Diet Coke when we go out.
If you do want a glass of something, again, make it the occasion and not the norm.
Recently I had an Aperol spritz in memory of my dad, who passed away last year, and a glass of champagne when I got the first copy of my new book.
Navigating the world of cancer and diet can feel overwhelming, but the key is to focus on what you can control.
Small, sustainable changes to eating habits can make a big difference in how you feel and reduce your risk of recurrence.
Perfection isn’t the goal. What matters is making informed choices based on evidence, not fear or pseudo-science.
Trust your medical team, seek advice from reputable sources like those I’ve mentioned, and be kind to yourself.
Why I don’t bother with supplements
Most cancer patients wonder if they should start taking supplements – I know I did.
The truth is, if you’re eating a healthy, balanced diet, you don’t need them. You’ll get all the vitamins and minerals you need from your diet.
Over-supplementation can even be harmful, as high doses of certain vitamins can interfere with treatment. High doses of Vitamin C may actually prevent radiotherapy working properly, some evidence suggests.
Turmeric and St John’s wort are just two of the common supplements that stop the function of tamoxifen, a hormone-blocking drug many breast cancer patients use.
Some supplements, in excess, can actually cause cancer. For example, beta-carotene may increase the risk of lung cancer in people who smoke.
And if they’re not doing harm, most of them end up in the toilet as your kidneys get rid of the excess that your body doesn’t need.
Cancer patients should always consult their oncologist before they start taking any supplements.
