Bowel cancer ranks as one of Australia’s most common cancers, especially for people aged over 50. This is one form of cancer where diet and lifestyle choices play a big part in changing a person’s risk of developing it. That makes it a good news story because lifestyle factors are changeable. Here I outline the key lifestyle habits to consider looking at.
Bowel cancer (also called colorectal or colon cancer) is the second biggest killer of Australians from cancer each year. Over 16,000 people are diagnosed with bowel cancer every year in Australia.
Bowel cancer can occur in any part of the colon or rectum, either growing from the inner lining of the bowel or from small growths on the bowel wall. Undetected, bowel cancer can spread into the wall of the bowel, the lymph nodes and then on to other organs.
Lifestyle factors account for half of all bowel cancer cases. Another quarter of cases are explained by genetics and family history. Not eating enough fibre, having too much red and processed meat, obesity (especially if the fat is around the abdomen), smoking, physical inactivity and alcohol are the key lifestyle factors with the most evidence for upping the risk of colorectal cancer.
So it is timely that only this month, the World Cancer Research Fund (WCRF) put out a major update into the lifestyle factors linked to bowel cancer.
Bowel cancer and lifestyle: the WCRF update
The World Cancer Research Fund is the world’s leading authority on the link between diet, weight, physical activity and cancer. When they put out reports, you can count on the information being backed by the world’s leading cancer scientists and a wealth of research.
Way back in 2007, the WCRF made some clear recommendations into lifestyle factors that influence bowel cancer risk. But research is never static, and recommendations are continually updated as new information becomes available. That is why the WCRF publishes updates as part of their Continuous Update Project. Among experts worldwide, the updates are a trusted, authoritative scientific resource, which underpins current guidelines and policy for cancer prevention
So here we have hot off the press the latest update: a new report on colorectal cancer. For the report, the global scientific research on diet, nutrition, physical activity and colorectal cancer was collected and analysed by a research team at Imperial College London, and then assessed by an independent panel of leading international scientists.
At 111 pages in length, the report is a lot to digest. But fear not that you need to wade through it all. The WCRF has produced an awesome infographic giving you the summary which sits below. After looking over the infographic, I will go into a bit more depth into five of the key factors.
If you want more information on the other factors linked to bowel cancer, then the full report has you sorted. And for a bonus, near the end of this article, I will look at the one factor that may have caught your attention on the infographic. And that is how your height can affect cancer risk. Don’t worry, there is nothing you can do about it, so focus instead on the other five areas!
1. Eat more wholegrains
There is a good reason why wholegrains feature in dietary guidelines around the world. And it is not to annoy those who are a bit too ingrained (see what I did there?) to low-carb or Paleo diets. Just how good wholegrains are for us was unveiled in a recent major scientific review looking at diet and chronic disease.
Covering decades of research and hundreds of studies, the review found that plant foods, especially wholegrain foods, were linked to a lower risk of type 2 diabetes, overweight and obesity, cancer and cardiovascular disease.
So when the WCRF looked at foods that can decrease the risk of bowel cancer, wholegrains scored high marks. Wholegrains are a source of dietary fibre which on its own can help reduce bowel cancer risk. Fermentation of fibre in the colon results in the production of short-chain fatty acids that lower the pH of the colon. A lower pH slows down the proliferation of cancer cells and decreases the production of toxic by-products.
Wholegrains are rich in antioxidants, including trace minerals and phenolic compounds, which have been proposed to be important in cancer prevention. The fibre in wholegrains can also speed up the transit time of food through the gut. Fibre also increases the bulk of stools and even help reduce the risk of insulin resistance.
2. More fibre for the win
Following on from the benefits of wholegrains, eating more fibre will help cut the risk of colorectal cancer. Which is another way of saying to eat more plant-based foods as that is the only place you’ll find fibre in your diet.
Fruits vegetables and beans are all great sources of fibre. And of course, wholegrain foods too, just in case you skipped reading the previous section.
3. Eat less red meat
People who eat a diet low in processed and red meat are less likely to develop bowel cancer. This link is nothing new and only in 2015, the International Agency for Research on Cancer (IARC) released a report investigating how likely red meat and processed meats are to cause cancer. The IARC concluded that processed meat and also likely red meat are linked to causing colorectal cancer.
Yet even the highest-level committee members of the IARC were not saying that if you eat a sausage you are a candidate for cancer. What they were warning about was that if processed meats were a daily feature of your diet, your risk of bowel cancer would go up.
So what is it about red and processed meats that can make them carcinogenic? The answer isn’t certain, but several plausible mechanisms have been proposed.
The first culprit is the haemoglobin pigment that gives red meat its colour. Haemoglobin breaks down to a family of chemicals called N-nitroso compounds in the gut. These compounds can damage the cells that line the bowel, causing them to divide and replicate more.
A second candidate could be the actual cooking process of red meat itself, especially grilling or barbequing. The combination of high temperatures and charring of meat produces chemicals on the surface of the meat that may increase the risk of colon cancer. One simple way to reduce the formation of these compounds is to marinate meat first. Think of it as a protective layer on the meat, but with the added bonus of extra taste.
Yet another theory is that the high iron content of meat could be the culprit. Iron is important for our health, but too much of it can place a higher oxidative stress (a process not unlike ‘rusting’) on the body, and damage cells lining the large bowel.
While a sausage sandwich every now and then isn’t going to do you much harm, if you are eating a lot of processed and red meat then it could be a good idea to try to cut down. The World Cancer Research Fund recommends eating no more than 500 grams of cooked red meat per week. And if you eat processed meat, really keep that to a minimum. Chicken and fish make excellent alternatives to red meat. Or you could even consider having more vegetarian meals in your diet. Time to get on the #MeatFreeMonday trend.
4. Get more active
Physical activity is recognised as a potent ‘cancer-preventing’ habit. Estimates link regular physical activity to a 20 to 40 percent lower risk of colon and post-menopausal breast cancer. There is also a potential benefit of exercise in lowering prostate cancer risk too.
Besides its cancer-prevention benefit, physical activity plays a large part in preventing heart disease and diabetes so the health benefits really add up.
In the WCRF report, the evidence was strong and consistent that high levels of recreational physical activity were protective against colon cancer. Physical activity helps reduce body fatness (which is linked to colon cancer risk) which leads to a reduction in insulin resistance and inflammation – both of which are part of colorectal cancer development.
The more active you are, the greater the benefits you can gain and it is never too late to start.
And as an aside, an evolving field of research is looking at how physical activity can help people already diagnosed with cancer. Several research studies are now linking regular physical activity after a cancer diagnosis with lower rates of cancer-related mortality, particularly from breast and colorectal cancer. These findings are important when you consider that thanks to earlier detection and improved treatments, more people than ever are surviving cancer.
5. Keep body weight in check
Keeping a healthy weight not only cuts your risk of bowel cancer, but could also reduce your risk of nine other types of cancer too. The evidence for bowel cancer and excess body weight in the WCRF report was consistent with a clear dose-response: meaning more weight equates to a higher cancer risk.
The link between excess weight and cancer could be from how our bodies can change hormone levels and produce chemical messengers, which in turn can increase cancer risk. High body fatness is associated with increased levels of insulin, which can promote cell growth and inhibit normal programmed cell death (called apoptosis).
Obesity is normally seen together with chronic low-level inflammation, which over time can cause DNA damage that leads to cancer. People who are overweight or obese are more likely to have conditions that are linked to or that cause chronic local inflammation.
Losing weight is easier said than done, and the WCRF don’t recommend any specific type of diet. Focus first on the wins you can achieve for the other lifestyle factors linked to cancer risk. Then consider a dietary change that connects with you – there is no one best way to lose weight.
Don’t be tall? WTF?
Here was a surprising one: being tall elevates the risk of colorectal cancer. Not much anyone can do about that one I’m afraid, but why is it so?
How tall a person grows is influenced partly by their genes and partly by the nutritional quality and quantity of their diet during the growing phases of their life. A higher growth rate is a marker for more growth hormones and other growth factors which while helping a person reach their peak potential height, also do a nice job of promoting too much cell growth. Uncontrolled cell growth is what cancer is after all.
Tall people also have more cells in their body, so more opportunities for a tumour to develop. And just like a giraffe with a long neck, tall people have longer intestines so more opportunities for exposure to cancer-promoting agents in the large intestine.
It is not all bad news though for the beanpoles amongst us. Being taller appears to be beneficial when it comes to preventing some other diseases such as diabetes, strokes and heart attacks.
Recommendations to live by
With colorectal cancer rates expected to rise worldwide, it is vital that people are aware that there are simple things they can do to help prevent the disease.
Swapping out some red and processed meat for fish or beans, or going for wholegrain rice instead of white rice are just a few tips for how people can work towards reducing their risk of colorectal cancer.
Keeping as healthy a weight as possible is not only important for preventing colorectal cancer. It also is key for reducing the risk of many other chronic diseases, including many other common cancers. And adding in some extra recreational activity will not only help with weight, but also have a host of other health benefits.
Bowel cancer may be one of the most common cancers seen in the Western world, but there is enough compelling evidence to show that by making healthy lifestyle changes, each person can significantly cut their risk.