Meaty issue at heart of cancer risk

Joanna Lumley reckons that being a vegetarian keeps cancer at bay. So what’s the scientific evidence for links between eating meat and cancer?

CAN BEING a vegetarian help protect you from cancer? Joanna Lumley appears to think so, based on her comments reported in the Sunday Timesearlier this month.

The actor claimed not to have had any cancer scares “because I’m a vegetarian”. She also shared her “feeling” that cancer could be linked to growth hormones being put into animals for meat production and that “a huge lobby for the meat industry” stopped people from speaking out.

But what do the scientific studies show? Is meat consumption linked with an increased risk of developing cancer? The answer is not straightforward, but the evidence suggests that limiting your intake of red meat and processed meat would be a wise choice.

“There is a link between meat consumption and cancer although it is very controversial,” says John Reynolds, professor of surgery at Trinity College Dublin and St James’s Hospital.

“It’s very difficult to do the sorts of studies that can definitively associate any element of the diet and cancer.

“The epidemiological studies are cohort or case control studies but they very often can’t control for other foods that people take and for their exercise and lifestyle and body weight or what they ate as children . . . So the science behind it is difficult, but the epidemiological studies would show that red meat and processed meat is almost certainly significantly associated with colorectal cancer.”

In particular, Prof Reynolds cites a 2007 report from the American Institute of Cancer Research and the World Cancer Research Fund.

“That would suggest that there may be about a 20 to 25 per cent increased risk of colorectal cancer from either red meat or processed meat,” he says.

“The relative risk compared to someone who eats very little meat – the 20 per cent increased risk – in real terms, that can be quite small but it is still statistically significant.”

The dose may also be a factor, he adds. “There are also some studies – more with bowel or colorectal cancer than with other cancers – that would suggest that the greater the quantities of red meat or processed meat that you eat, the greater the risk.”

For cancers of the oesophagus, pancreas, stomach, prostate and breast, the evidence suggesting that red meat or processed meat relates to them is limited, according to Reynolds: “The literature is conflicting in that regard.”

Meanwhile, the mechanisms behind any links between meat consumption and cancer remain unclear. One theory is that nitrates and nitrites in processed meats are converted to potentially cancer-triggering nitrosamines in the gut.

Another points the finger at chemicals that can form when red meat is cooked at high temperatures, such as heterocyclic amines and polycyclic aromatic hydrocarbons. “In the test tube or in certain experimental conditions they can be pro-carcinogenic,” says Reynolds.

Meanwhile, obesity – which may be helped along by fatty red and processed meats – has also been linked to an increased risk of particular cancers.

So what are consumers to do? The bottom line is to limit consumption of red and processed meats and to maintain a healthy lifestyle, says Reynolds.

“You don’t want to have meat and nothing but meat as your staple diet, you have got to prevent obesity if you can, exercise as much as you can during the week, eat five a day of vegetables and fruits and have more complex carbohydrates,” he says.

The Vegetarian Society of Ireland echoes the healthy lifestyle ethos, pointing to to a study published last year in the British Journal of Cancer that examined data from British studies of cancer incidence in meat eaters, fish eaters and vegetarians. The study concluded that “the incidence of some cancers may be lower in fish eaters and vegetarians than in meat eaters”.

Dr Marian Faughnan, chief specialist in nutrition at Safefood, also highlights the studies on red and processed meats and bowel cancer, and she offers suggestions on cutting back.

“Our message is to be reasonable around portion size and to choose leaner cuts,” she says. “Men often have large portions – but you don’t need an eight- or 12-ounce steak.”

However, she notes that lean, unprocessed red meat can be an important source of iron in the diet, and suggests that women and children who may be vulnerable to low iron levels have two portions per week.

A vegetarian diet with plenty of fruit and vegetables can be a healthy lifestyle choice, according to Faughnan, but for some people, cutting out meat altogether would be a drastic change they are unlikely to stick to.

So she suggests reducing red meat consumption to a couple of times a week and trimming the visible fat off it, and limiting processed meats to once a week. “It’s about trying to achieve more of a balance across the board,” she says.

The recommendation from the Irish Cancer Society is to limit intake to 500g or 18oz of cooked lean red meat per week (800g/28oz of lean raw meat). As for processed meats like sausages, hams, salami, pastrami, hot dogs and rashers, its line is to limit or avoid them.

“Choosing not to include processed meat in your diet can make a difference to your risk of cancer, ” it advises.