Is our diet – too much red meat and too little fibre – to blame for our high rate of bowel cancer?
For Auckland dietitian Kate Ellison, developing bowel cancer at 34 was “just the biggest kind of slap in the face. Food and nutrition have always been really important to me and I’ve always practised what I’ve preached by eating well. It was shocking for me.”
Now 41, Ellison has been a dietitian for 17 years. She knows better than most the importance of a balanced diet with particular emphasis on vegetables, fruit and fibre-rich whole grains. “To get cancer at 34, in my mind, this was just not who I was. I couldn’t believe it. I thought this wasn’t the path for me, this shouldn’t be happening to me. Then there was the anger at having eaten well and still developing it. Even during my university days at Otago, not every single meal was great, but compared with anyone else, I was the one making the good food choices in my age group.”
Ellison has no family history of the disease, and it’s cases like hers that perplex patients and confound the scientific theories about the importance of diet in cancer – specifically bowel cancer. Despite her experience, she still believes there is a “large dietary component” to the development of bowel cancer, but it’s obviously not the sole factor, and it’s a complicated subject.
Ellison isn’t the only one conflicted – even the medical experts can’t agree. Although one of our foremost specialists in colorectal cancer, Christchurch-based University of Otago professor Frank Frizelle, puts the likely influence of eating habits on bowel cancer as low as 15-30%, other doctors estimate diets high in red meat and low in fibre could increase risk by up to 60%.
In the diet-bowel cancer debate in New Zealand, no two people better illustrate the division of opinion in the medical profession than Frizelle and retired Auckland GP and diet book author Michael Cooper, a past president of the New Zealand Medical Association.
Cooper believes, on the basis of long-running international studies involving hundreds of thousands of participants, that red meat and a lack of fibre have been firmly fingered as the prime culprits, and the profession has been scandalously slow in advising us to radically overhaul our eating habits.
For years, he’s been contacting key medical opinion leaders and writing letters and papers exhorting specialists, schools of medicine, professional colleges and the Medical Association to spearhead a public education push similar in scale to the campaign against smoking. His efforts have left him profoundly frustrated and accusing his former colleagues of tunnel vision. “They’re in their own little tiny world and they don’t move outside that. But the public has a right to know. There’s enough information here, but the public isn’t being informed.”
He believes the evidence linking red meat and low fibre intake to bowel cancer and the delay in doctors pushing dietary change for prevention is akin to the medical profession’s slow response in the 1960s and 70s to the epidemiological research linking smoking with lung cancer. And, he says, prevention matters – New Zealand women have the highest rate of bowel cancer in the world, and New Zealand men the third-highest. Every month, 100 people in this country die from the disease.
It’s more than a decade since the Lancet published the first results of the European Prospective Investigation into Cancer and Nutrition (EPIC) study, involving nearly 520,000 people aged 25-70 who were followed for 10 years. It concluded populations with low-fibre diets could reduce their risk of bowel cancer by 40% by doubling their fibre intake. And in 2007, another study with more than half a million participants, the National Institutes of Health’s Diet and Health Study, reported people with the highest red-meat intake had 20-60% higher rates of colorectal and other cancers. The studies found eating fish reduced the risk of bowel cancer, while poultry intake was neutral.
In 2011, a panel of judges for the World Cancer Research Fund/American Institute for Cancer Research reported the evidence that fibre protected against bowel cancer and red and processed meat caused it was now “convincing”. The panel also concluded higher intakes of garlic, milk and calcium probably decreased risk.
In an opinion piece rejected for publication in the New Zealand Medical Journal in February, Cooper wrote that “these momentous findings pave the way to prevent this cancer. They fit the New Zealand and Australian diets like a glove. Red meat, along with sausages, ham, bacon and salami, plus fibre-depleted salads, white bread and bakery items, fibre-depleted cereals (most of them), sugar and takeaways are basic to the eating cultures of Australia and New Zealand.”
Independent reviewers responded that there was also evidence from randomised trials of dietary interventions in heart disease that showed, despite improving heart disease, low-fat diets did not reduce the incidence of colorectal cancer. Correlation, they said, didn’t prove cause and effect. “Two events are occurring at the same time – namely that colorectal cancer risk is increasing as ingestion of red meat is increasing. A similar graph could be drawn for many other environmental factors.”
His rejection email was signed off by the Medical Journal’s editor-in-chief – Frank Frizelle.
Frizelle says he’s not blocking the publication of views he disagrees with – only one in eight medical journal submissions are accepted and all articles are peer-reviewed by at least two external experts before a decision is made by the editorial review board. “All we do is ensure what we publish is well written and has good scientific evidence/design behind it. I think red meat and fibre have been well thrashed out.”
Frizelle says of the roughly 93% of colorectal cancers that don’t have a known inherited genetic cause, “a lot of rubbish is talked” about what causes them. “You’ll find people saying alcohol and diet, but when you control for other factors, most of those things disappear. It’s not all about diet. It’s much more complicated than that. It’s a small component.”
He points out sheep get bowel cancer too – “and how much meat do sheep eat?” In 2008, Frizelle co-authored a paper on the cancers, which said New Zealand sheep developed small-intestine cancers more frequently than animals elsewhere in the world and suggested this could be due to an environmental carcinogen that could also affect humans.
The sheep research, though, has “died out”, he says. “Research in New Zealand is driven by where the dollar is, trying to make sheep bigger and with better wool.” Sheep bowel cancer was of interest to academics, he says, but not funders.
That’s not to say Frizelle doesn’t favour reducing meat consumption and upping our vegetable intake – he certainly does. “Without doubt, it has some benefit in general for your health, but it’s not, ‘Eat that and you won’t get bowel cancer.’ It has other gains involving heart disease and obesity and we know the fatter you are the greater your chance of getting bowel cancer, and there’s a whole pile of different reasons for that. Diet itself isn’t as simple as people would like to make out as a cause of bowel cancer.”
Most people with bowel cancer, he says, “eat an exceptionally healthy diet”. Vegetarians are often angry and bewildered when diagnosed. “One just about ripped my head off. She said, ‘I’ve been a vegetarian since I was 14. I can’t possibly have it.’ Being a vegetarian may reduce your risk, but it’s not going to stop it.”
THE HARD WAY
Rotorua mother of five Janet Du Fall, 54, and Auckland biologist Michael Anderson, 35, have learnt that the hard way. Du Fall had been a vegetarian for 10 years before her bowel cancer was diagnosed last year; Anderson for 13 years before his diagnosis in 2012. Neither has a strong family history, although Du Fall’s paternal aunt died of the disease in her fifties in the late 1970s and two of Anderson’s grandparents had had it. Genetic tests in Anderson’s case proved negative.
Du Fall says she’d never really enjoyed meat, but stopped eating it altogether in her early forties when she was diagnosed with a polycystic kidney complaint. Although she grew up in a “meat and three vege” family growing up, they’d never eaten huge portions, wholemeal bread was always her preference and “Mum had a lot of fruit and veges in the house and so did I”.
She says she regularly walked 15km a week and has never been overweight, always tipping the scales at around 50kg, despite having a sweet tooth. Indeed, if there was any dietary failing, she says, it was sugar, and she has now radically reduced her refined sugar intake, is taking high-potency vitamin C daily and is regularly juicing fruit and veges.
Like Ellison, she believes diet is involved somehow. “To what extent I don’t know – but it must be.”
Her chemotherapy finished in August and she’s now looking forward to the birth of her first two grandchildren. “I see myself as a survivor but I’m also conscious that in terms of where to from here, if I want to stay cancer-free I can’t go back to eating the way I did before. I’m conscious, and will be forever, about reducing refined sugar and eating whole foods.”
Massey University biologist Michael Anderson suffered from severe anaemia following his bowel cancer surgery, which forced him to include meat in his diet. “I was craving protein. At first it seemed really odd to eat meat again and in some ways I felt guilty. But because it was for my health, I needed to.”
He restricts his intake to one meal a week and also has chicken and fish. “I ate bacon for six weeks and I loved it, and then found out I shouldn’t be eating processed meats.”
As a scientist, he’s researched bowel cancer papers since his diagnosis and has been surprised to find one large study that showed the relative risk to vegetarians and red-meat eaters was almost identical.
That’s not surprising, says Wellington-based University of Otago cancer epidemiologist associate professor Diana Sarfati, because “nutritional epidemiology is absolutely full of contradictory findings. It’s the nature of the beast.”
The problem is, she says, that any individual’s diet is “really complex”, with many elements to it. “If you’re thinking about cancer, you’re thinking about a lifetime of a diet, so you’ve got to add many orders of magnitude, trying to ascertain the impact of that on the outcome decades later.”
Interactions in individual diets could also make a difference. “This is a made-up example, but it could be eating red meat is very important, but less important if you also eat spinach.”
And, she says, there’s the difficulty of deciding at what point diet counts most, even in prospective studies. “It may be what they were eating as a child is the critical thing.” And then what happens if you’re a vegetarian or vegan for a few years? How does that compare with lifelong dietary patterns?
But Sarfati does agree the evidence of an association between red-meat consumption and colorectal cancer is convincing, based on the epidemiological studies, and that eating fish reduces risk.
“It would be really great to have a better understanding of the interactions between the different elements of diet, and between diet and gut flora and the mechanisms of the action of both those things. Whether or not we can achieve that in my lifetime is another issue altogether.”
DIET VS BACTERIA
The role of gut bacteria in bowel cancer is a key research interest of Frizelle and his University of Otago colleague, senior research fellow Jacqui Keenan, who have together published a number of papers. “There is a role for diet,” says Keenan, “but it may not be perhaps the role that people up until now have perceived it to be.”
We have trillions of bacteria in our gut, most of them going about their business of processing the food we eat in a trouble-free and beneficial way. We’re colonised with these bacteria at a very early age. In the birth canal, we’re exposed to our mother’s bacteria and we’re also exposed to them in the environment after birth. Babies born by Caesarean section are colonised with fewer bacterial species and this could be a disadvantage, says Keenan – the more diverse the bacteria, the better off you are. Like our fingerprints, each of us has a different population of gut bacteria – our microbiome – and those bacteria will respond differently depending on what food we eat, and even what antibiotics we take.
Keenan and Frizelle’s theory is that some of us are colonised in the early years with driver or rogue bacteria that are able to interact with the mucosal surface of the gut, causing unsymptomatic inflammation, or even producing a toxin that directly damages the DNA in cells. “I think the rogues have been there from the start, but because you have all these other good bacteria around them, they’ve hidden themselves, and you may have all of that going on and nobody is aware of it, over many years,” says Keenan.
The best example of a rogue or driver bacterium directly influencing cancer has been the identification of Helicobacter pylori, which causes stomach cancer. “It’s the same sort of model,” she says.
Keenan is trying to identify the rogue bacterium and her current top suspect is a toxin-producing strain known as Bacteroides fragilis. A possible link was first reported by Turkish investigators in 2006, but in a pilot study in Christchurch reported at international meetings this year, Keenan and her colleagues found 19.6% of patients with bowel cancer carried the toxic strain, compared to only 7.4% of people in the non-cancer control group. She says although around 85% of us will carry Bacteroides fragilis, a much smaller number will have the toxin-producing type.
She’s now trying to get funding to widen the pilot study and is collecting stool samples from people attending GPs with possible bowel cancer symptoms to find out if the toxin-producing bacterium shows up pre-diagnosis. If antibodies to the bacterium could be found in the blood, it could be a potentially valuable biomarker for early-intervention strategies.
More money is also needed for another big bowel-cancer research project, at the Dunedin School of Medicine, where epidemiologist associate professor Brian Cox is investigating whether the milk-in-schools programme, which ran from 1937-1967, might have protected those children from developing the disease later in life.
In 2011, Cox and colleague Dr Mary Jane Sneyd reported that bowel cancer was reduced by 30% for those who took part in the programme. The biggest milk drinkers had the lowest risk – an impressive reduction of 38%. Many schools in Southland, which has the highest rate of bowel cancer in New Zealand, opted out of the school milk scheme in 1950, after being given the option by the provincial education board. For people who started school in Southland between 1951 and 1967, only 36% had had school milk at least once, compared with 85% of children in other regions.
Cox says the findings need to be further investigated, and another $150,000 is needed to continue the work, which would also examine the impact of other dietary components such as red meat. He says school milk doesn’t fully explain Otago-Southland’s historically high rate of bowel cancer compared with the rest of the country.
THE MILK LINK
Dunedin bowel cancer patient, businessman Roy Shanks, 59, agrees. He remembers being a school milk monitor in primary school and says he always loved his milk. “We had a family of four boys and we drank a lot of milk – we had six pint bottles delivered every day.”
Shanks, the father of four children, including Commonwealth Games cycling gold medallist Alison, says he was brought up in a “red meat and vege” household typical of the era. They also ate chicken and fish but minimal processed meat. “Ham was once a year, at Christmas.”
Shanks, who was operated on in August last year and is undergoing chemotherapy for secondaries in the liver, says examining the cause of his cancer hasn’t been a priority but “it is something I wonder about”.
During chemotherapy, he often talks to other patients who are also asking why. “Without exception, everyone seems to have been not excessive one way or the other [with their diet].”
He says he’d also asked his oncologist, who replied, “The most probable cause is diet.” “I didn’t push it because I’ve been more looking forward rather than looking back.”
Some of the best evidence of a dietary link to bowel cancer comes in migrant studies. If you grow up in Japan, for example, and move to New Zealand before 30, your risk will increase until it ends up the same as someone born and bred here. After 30, the risk stays at the Japanese rate.
But Southern District Health Board medical oncologist and University of Otago senior lecturer Chris Jackson says there’s obviously more to it than diet. “The United States, which probably has the worst diet in the Western world – high in all the things we say are bad – has considerably lower rates than New Zealand.”
Jackson is heading a three-year, $1 million study on bowel cancer patient outcomes, which is due to report in March. He says international research has shown “Western” rather than “prudent” diets are associated with a higher risk of recurrence and death in colon cancer patients who had had surgery and chemotherapy. But he adds that examining diet isn’t part of the latest New Zealand study because it was so “extraordinarily complex” and there are many other influences on how patients fare, including “considerable” geographical variation in their care.
He says getting populations to change their diets and exercise more is extremely difficult. Anti-smoking programmes had been successful largely because of price increases. “If you want to say what are the things you can do as a society, then alcohol reduction and a colonoscopic screening programme would be the two very clear things to reduce the impact of bowel cancer.
“But at an individual level, should you eat five portions of fruit and veges a day? Absolutely. Should you eat white meat twice a week? Absolutely. Should you keep your red-meat portions down to a modest level? Absolutely. But just saying all we need to do is change our diet is a very simplistic and reductionist way of looking at a problem that is quite complex.”
Like Frizelle, Auckland associate professor of colorectal cancer surgery Ian Bissett says the lifelong vegetarians he treats find it particularly difficult to accept their diagnosis. “But whether they are vegetarian or not, there is this existential question, ‘Why me?’, particularly if they’ve been active, watched their weight and been careful about diet. Obviously, I don’t really have an answer except that it’s common in New Zealand and it’s not usually the fault of the person who gets it, which is sort of the question they’re asking – ‘What have I done wrong? How could I have avoided this when I’ve lived my life as well as I have?’ I tell them some of the risk is actually related to what their genes are like, and that’s not something they can do a whole lot about.”
His best prevention advice, then? “Probably choosing your parents; although you might say choosing your country might be even more important.”
For patients who develop bowel cancer under the age of 40, Bissett says, there’s likely to be some sort of genetic predisposition, even if the markers for currently recognised syndromes can’t be found. A “significant minority” – about 15% of bowel cancer patients – seem to have a familial disposition, even if they don’t have one of the known genetic syndromes linked to the disease.
University of Auckland geneticist associate professor Andrew Shelling says only about 5% of colorectal cancers have a purely genetic cause. “They’re rather exceptional cases – situations where no matter what other risk factors you’ve got, you’re virtually predetermined to get it at some time in your life and younger than you might expect.”
For Cooper, the dietary prescription he preaches has served him well. Cooper largely stopped eating meat and started upping his fibre intake 30 years ago, in response to the pioneering work of Irish surgeon Denis Burkitt, who compared the pattern of diseases in Africa and the West and first linked low fibre to bowel cancer. Fit, wiry and, at 86, enviably spry, Cooper is a walking advertisement for living life by Burkitt’s rules.
He’s not worried, he says, about his own generation, but his grandchildren’s. “I have good friends desperate that their grandchildren get enough meat – you know, Dan Carter stuff. They need the iron.”
That alarms him, along with dietary trends like the Paleo movement, which advocates against carbohydrates such as potatoes and bread in favour of proteins such as red meat.
“When a person has the fibre-rich diet of most of the Third World, the content of the bowel is emptied in about 36 hours. In our society, constipation is rife because women particularly are scared of high-fibre foods.”
In his last 10 years as a medical practitioner, Cooper worked in an obesity clinic, treating mostly women. “Over and over again, hour by hour, when we asked about fibre, they say they ate salads every day and they never touched bread or potatoes. And these were big, big women. I said, ‘If you’re eating all this salad, how come you’re here?’ Women need to eat 35g of fibre a day. An entire lettuce has only 3g.”
Cooper reckons specialists find prevention boring, because results take too long – certainly much longer than a quick few hours of surgery to remove a tumour – and their focus on colonoscopic screening will do nothing to reduce New Zealand’s “appalling incidence” of bowel cancer and its precursors, polyps. He prefers to take the line of Harvard biologist John Cairns, who compared eradicating cancer with eradicating infectious diseases 30 years ago, saying that in the history of medicine, treatment alone had never eradicated a significant disease. “The death rates from malaria, cholera, typhus, tuberculosis, scurvy, pellagra and other scourges have dwindled because humankind has learnt how to prevent these diseases. To put most of the effort into treatment is to deny all precedent.”
And this is why Cooper plans to keep battling to get the prevention message out, despite the specialists who, well, pooh-pooh his ideas.
“I think their minds are closed. They just like their fillet steak.”
Startling research from the US indicates new diagnoses of colorectal cancer in younger people will nearly double by 2030. The University of Texas study suggests in the next 15 years more than one in 10 colon cancers and one in four rectal cancers will be diagnosed in patients aged 20-34. Nearly 137,000 people are diagnosed with colorectal cancer in the US annually and more than 50,000 die of the disease. But there has been a steady decline in colorectal cancer in older patients, largely because of screening and prevention efforts. Colorectal cancer is America’s third most common fatal cancer.
IN THE FAMILY
For patients who develop bowel cancer under 40, like Anderson, Ellison and Auckland doctor Jared Noel, who died in October aged 33, there’s likely to be some sort of genetic predisposition, even if the markers for currently recognised syndromes can’t be found. Noel’s battle to stay alive long enough to see the birth of his first baby gained national attention last year. An upcoming book documents his experience with cancer.
Follow the Listener on Twitter or Facebook.