Long live the greens

Scientific evidence is mounting that certain foods could have anti-cancer properties, writes CLAIRE O'CONNELL

COULD YOU protect yourself against cancer by choosing wisely what you put on your plate?

Tantalising clues suggest that certain foods have protective, cancer-fighting properties, and while pinning those activities down scientifically is fraught with difficulty, some contenders like broccoli, soy, green tea and even the ancient spice turmeric show star anti-cancer qualities that are hard to ignore.

Yet despite the mounting evidence, many of us underappreciate the links between diet and cancer, according to consultant surgeon John Reynolds, professor of surgery at Trinity College Dublin and St James’s Hospital.

And if you go looking for information on using food to prevent cancer, many popular books and programmes make scientifically unvalidated claims, he cautions. “There’s a huge amount of nonsense out there that’s based on no science, pseudoscience or wrong interpretation of the existing science.”

So where is the good science? Many of the links between food and cancer in humans have come from studies looking at large populations over time, explains Reynolds.

“Societies that eat a lot of fat and a lot of red meat, we know they are the societies where there is a lot of breast, prostate and colon cancer and a certain type of oesophageal cancer, and societies that don’t eat a lot of red meat and fat have lower rates of those cancers,” he says. “So you are looking at the relative risks and correlations, that’s at a macro level.”

But to pin a particular food’s effects down more specifically is far trickier, he notes. “To do a trial of extra soya or extra tomatoes in the diet basically as a cancer-prevention approach, the logistics of that are daunting. You would need thousands upon thousands of patients, and you would need so many other things controlled for – their weight, exercise, regular diet. It makes it very difficult.”

In the lab though, some foods demonstrate the ability to affect cancer-related processes in isolated cells. A study carried out at University College Cork recently captured headlines when the researchers showed that curcumin, a component of the spice turmeric, could halt the growth of oesophageal cancer cells.

The UCC research added to the emerging picture of curcumin as an anti-cancer agent, and these kinds of study can highlight interesting biological properties of particular foods, comments Reynolds.

Evidence is also stacking up for green tea, soya and cruciferous vegetables like cabbage and broccoli as promising anti-cancer foods.

So how do they work? They contain compounds that could be targeting cancer-related processes like cell growth, damage and inflammation, and some may even block tumours from building the blood supply they need to grow and spread to other parts of the body, he explains.

Reynolds points out that by middle age, many people can already be carrying small tumours which, if left as they are, cause no trouble. “That has been shown in autopsy studies of people who died in road traffic accidents and the like,” he says. “It’s well established that for breast, prostate and thyroid these microcancers exist, but in the vast majority of cases thank goodness they never amount to anything.”

One way that foods could help keep such mini-tumours in check is by blocking the “angiogenesis” process that builds up their blood supply, and there’s evidence that green tea could do just that, according to Reynolds.

“There’s excellent science published in the best journals like Nature that there is something in green tea that inhibits angiogenesis in an experimental model, even though it’s very difficult to apply that in studies in man,” he says.

“We don’t need to have everything studied in the way a new drug is studied to apply and adapt it and maybe incorporate it into your life, because there is definitely something there.”

The evidence for soy as an anti-cancer food is not quite as compelling, but nonetheless populations that eat it tend to have lower rates of hormone-related cancers like breast and prostate cancer.

“Soy is very interesting. It contains genistein, one of the isoflavones, which is very similar to the hormone oestrogen and also very similar to a drug called tamoxifen, which is the most commonly used drug in the treatment of breast cancer,” explains Reynolds.

“There would be some reasonable data in societies where they take a lot of soy when they are young of a lower incidence of breast cancer. Similarly, because it is a hormone-related cancer, prostate cancer is also purported to be reduced by it.”

Sources of genistein include soya beans and flour, but people with existing breast or prostate cancer should exercise caution, he notes. “Because it is oestrogen-like, there has been some concern based on studies, particularly in mice who have a cancer implanted into their system, that extra soy can promote the growth of the breast cancer.”

And eating whole foods as part of a balanced diet is without question better than taking supplements of suspected anti-cancer compounds, he adds.

But apart from good quality food, the quantity may matter as well – obesity is associated with a higher risk of developing certain cancers of the colon, oesophagus, kidney, breast (post-menopause) and womb.

“Obesity is rising in parallel with the increasing incidence of cancers in the Western world, and obesity can markedly increase the risk of developing and dying from a lot of different cancers, but it’s really only recently people that have appreciated that association,” says Reynolds. “Most people would have had it more in mind that it’s associated with heart disease and diabetes.”

The common link may involve chronic inflammation, which is often a feature of obesity, and Reynolds’ own work has been looking at links between obesity, inflammation and a type of oesophageal cancer.

“We have been studying how the patient’s own fat around the gut, the visceral fat, impacts on the behaviour of the actual cancer,” he says.

“We have found that the visceral fat in patients with oesophageal cancer is teeming with very active immune cells that by surrogate analysis can be associated with triggering the cancer switches and the inflammatory switches. So there are connections there and the science is intriguing.”

Overall, the emerging substantiated links between diet and cancer should be taken on board, according to Reynolds. “There’s something there – it would be foolish to ignore it and also foolish to overinterpret it,” he says.

“And I think a strategy over the next five to 10 years would be to marry hopefully good science, as best it can be done in a difficult area, with efforts towards highlighting the enjoyment and also the potentially real health benefits of good food in combination with dealing with obesity. I think that would be worth taking on.”

Anti-cancer foods: how they work

Scientific studies suggest that particular compounds occurring naturally in foods could help prevent or fight cancer. So what should be on the shopping list?

Cruciferous vegetables (including broccoli, cabbage, kale, cauliflower and Brussels sprouts): They may not always be the children’s favourite, but the crucifers pack a punch of glucosinolates, which break down in the body to form anti-cancer molecules.

Broccoli in particular provides sulphoraphane, which has been shown in the lab to trigger death in cancer cells. Source fresh vegetables, cook lightly and chew well.

Turmeric: The spice turmeric, which has been consumed for thousands of years, contains the compound curcumin, which appears to have anti-inflammatory effects and has also been shown to kill cancer cells in the lab. Eat black pepper at the same time, as it improves your ability to absorb curcumin.

Green tea: Green tea is a source of catechins, compounds that have been shown to inhibit the growth of cancer cells in the lab and could help block tumours from building up a blood supply in the body.

Information sourced from Foods to Fight Cancer by Prof Richard Béliveau and Dr Denis Gingras