We are what we eat – as the saying goes. It’s widely known that eating a ‘Mediterranean’ diet rich in fresh fruits and vegetables, lean proteins, whole grains, legumes and good fats can be a factor in a long and healthy life. But research suggests that some vegetables are more protective than others against various types of cancer.

Leading nutrition researcher Professor Richard Mithen has been studying the effects of different diets and foods on the development of cancer, and discovered that cruciferous vegetables (aka the brassica family), including broccoli, cauliflower, brussels sprouts, cabbage and kale, are particularly effective at slowing the progress of prostate cancer.

Although earlier research had indicated that eating tomatoes, and especially cooked tomatoes, slightly reduced the risk of prostate cancer, Professor Mithen says the evidence for crucifers is much stronger.  

In clinical trials with early-stage cancer patients, he tested the effectiveness and safety of dietary interventions based on eating cruciferous vegetables or their extracts. He asked men with localised prostate cancer on active surveillance to consume broccoli soup weekly, and found that it reduced biomarkers of prostate cancer progression, including PSA levels and urinary symptoms.

When he shared the results of his research, and lots of practical advice, with attendees at the 2023 Prostate Cancer Foundation of New Zealand conference, we knew we had to pass on this potentially life-changing information.

In particular, he has identified glucoraphanin as a potent anti-cancer agent.  

“When you eat it, what happens is that the bugs in your gut cleave off the glucose – they want to eat it themselves – and you end up with a compound called sulforaphane. It’s a mustard oil and you absorb it into your bloodstream and it goes into your cells – and your cells absolutely hate it. It’s really bad for the cells. It depletes a compound called glutathione and it puts the cell under stress, oxidative stress. But what happens is that the cell switches on all its repair mechanisms, all its detoxification enzymes, its cell defences. It excretes it from the body, the cell recovers then gets back to a healthy metabolism. It changes the gene expression profile and retunes your metabolism.”

For his study he and his team recruited men who were on active surveillance and at intermediate risk of prostate cancer, and asked them to eat broccoli soup each week for 12 months. “We compared their genes after the intervention to before and the results were consistent with if you have a lot of cruciferous vegetables in your diet, you may reduce the risk of cancer progression.”

Professor Mithen emphasised that his research is still ongoing and more studies are needed to confirm the optimal dose, duration and combination of dietary interventions for different cancer types and stages.  

But he cites a study conducted by the University of Southern California, which looked at the vegetable and fruit intake of men after diagnosis of low-intermediate risk prostate cancer to try to work out if there was an association between what they ate and the progression of their disease. It found that men eating cruciferous vegetables once every two or three days began to show a decrease in progression, and the effect was even more marked in those eating them every day.  

“Men in the fourth quartile of post-diagnostic cruciferous vegetable intake had a statistically significant 59% decreased risk of prostate cancer progression compared to men in the lowest quartile,” concluded the authors. “No other vegetable or fruit group was statistically significantly associated with risk of prostate cancer progression.”

Professor Mithen cautions that other lifestyle factors, such as exercise, weight management, giving up smoking and moderating your alcohol intake, are also important for cancer prevention and treatment.

He particularly recommends walking briskly for three hours each week, which a Californian study showed resulted in a significant reduction in the risk of progression of localised prostate cancer.  

“Eating broccoli, walking and going to the gym are actually doing the same thing,” he says. “Because when we eat these we’re inducing acute oxidative stress, and when you go to the gym or have a brisk walk and get a bit out of breath, your tissues are under stress. That switches on our natural defences and restores the metabolism – and we think this is what reduces the risk of various cancer clones expanding.”

This hypothesis is backed up by the results of an earlier study conducted in the USA, which gave men with prostate cancer high doses of antioxidant vitamin E, thinking it would reduce cancer rates. Instead, it increased the incidence of cancer, and had to be stopped early.

“And where do these antioxidant supplements fit in?” says Professor Mithen. “What they do is they stop our own defences from being switched on. They flood the system. And this is why we think taking high-dose antioxidants is probably not good for your health.”

Professor Mithen says there are no magic bullets for cancer prevention, but we can try and help ourselves by getting regular exercise and adopting a healthy diet including plenty of cruciferous vegetables. “It’s something that you can do and there’s no risk associated with it.”

The information provided in this article is for educational purposes only, and is not a substitute for professional medical advice. See your doctor for individual dietary advice.