We’re breast cancer doctors – and know claims the disease can be ‘avoided’ by lifestyle choices are unfounded Dr Liz O’Riordan and Professor Trisha Greenhalgh take a closer look at assertions made two weeks ago from another doctor

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It’s quite a claim: a woman can reduce her risk of developing breast cancer by 50 to 80 per cent, all by eating a healthy diet, avoiding alcohol and taking exercise. That’s according to Dr Kristi Funk, the surgeon who has treated celebrities including Angelina Jolie and Sheryl Crow.

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She makes these arguments in her book Breasts: An Owner’s Manual, which was published earlier this year, with an excerpt recently appearing in i.

As two doctors who also specialise in breast cancer – and have had the disease ourselves – we were surprised at Dr Funk’s conclusions. Reading her book, we were glad that she debunks alkaline diets as nonsense and explains the commonly quoted statistic of one in eight women getting breast cancer is often misunderstood as it applies over a whole lifetime and takes ageing into account, too.

Dispelling myths

She also very sensibly dispels myths that bras, deodorant and mobile phones cause cancer.

And yes, it’s true that some breast cancers are avoidable, as she writes. But from our work, we know the latest evidence simply does not support the claim that most breast cancers would be prevented if we all improved our lifestyles.

Research on breast cancer is accumulating rapidly and the most reliable sources are recent comprehensive summaries, known as systematic reviews, of all the research undertaken to date.

Reviews that have used statistical techniques to produce a weighted average of all relevant studies – known as meta-analyses – are the most useful.

Dr Funk has helpfully made the list of research articles she used when writing her book available online, but we are concerned that some of those sources are out of date. While Dr Funk’s list of sources includes several meta-analyses, some of them date from the early 2000s, so they do not incorporate the latest research.

Out of date sources

Using the most recent meta-analyses available, we have found that the proportion of pre-menopausal breast cancers that are attributable to being overweight or obese is zero; for post-menopausal breast cancers the figure is around 5 per cent.

We also found that the proportion of post-menopausal breast cancers attributable to all modifiable risk factors combined – diet, alcohol, smoking and physical activity – is less than 35 per cent.

In fact, the biggest risk factors for getting breast cancer are being born female and getting older – things you can’t change.

Traditional British diet

Dr Funk also produced an infographic that advised women to avoid milk and other dairy products in order to prevent breast cancer. This recommendation has no basis.

A meta-analysis published in 2011 found that consumption of dairy products was associated with a reduced risk of breast cancer and a more recent meta-analysis published in 2015 confirmed a “dose-response effect” – that the higher a woman’s intake of dairy products, the lower her risk of breast cancer.

Dr Funk’s infographic also suggested that breast cancer can be prevented by switching from a traditional British diet, with meat, fish, eggs and cheese as the main protein source, to one based predominantly on so-called “superfoods” such as quinoa, tofu and wild rice.

While some epidemiological studies suggest that consuming more soy products lowers the chance of developing breast cancer, this association is weak and has not yet been shown to be causal – it’s possible that people who eat soy diets may generally be healthier in other ways.

Regular red meat consumption has been linked in meta-analyses with a very small increased risk of developing breast cancer

Overall, however, the risk of developing breast cancer does not differ among people who identify as vegetarian, pesco-vegetarian or non-vegetarian.

Like many women who get breast cancer, we were both slim and sporty before our diagnosis. Trish has been a vegetarian for many years and both of us lead a healthy lifestyle. We were just unlucky, as Dr Funk acknowledges is an unfortunate fact of life.

Fad diets

As doctors, we caution patients against following fad diets. There is no single food that has been shown to cause breast cancer, nor is there any single food that will protect you from developing it or prevent it recurring.

Sugar is bad because it tends to make you put on weight, not because it “feeds” cancer cells. So if you have a sweet tooth, take sugar in moderation and monitor your weight.

If you do have the disease, or know someone who has it, we sympathise deeply. We’ve lived through it ourselves and we’ve looked after hundreds of patients with breast cancer.

Dr Liz O’Riordan, a consultant breast surgeon, and Professor Trisha Greenhalgh, a researcher at the University of Oxford, are the authors of ‘The Complete Guide to Breast Cancer: How to Feel Empowered and Take Control’ (£14.99, Penguin Random House), which will be released on 27 September