Bowel Cancer and Diet
April is bowel cancer awareness month, so we’re taking this opportunity to talk about bowel cancer and look at how we can make small changes to our diet to ensure we stand as best chance as we can to avoid it. A healthy gut starts with good nutrition!
What is bowel cancer?
Bowel cancer is the common name for the malignant tumours that form in the large bowel which comprises of the rectum and colon; it is also known as colorectal cancer. These cancers usually form from polyps, benign growths that appear in the colon, which accumulate as we age. We often don’t know we have them until we notice blood being passed when we go to the toilet and take the steps to have it investigated by medical specialists. Although polyps are benign, many will be removed, and so bleeding from the rectum should never be ignored. Catching polyps early could mean the difference between an uncomfortable investigative procedure called a colonoscopy every 3 to 5 years and developing full blown cancer.
Bowel cancer is highly associated with family history, so if you have a parent or a sibling with bowel cancer before the age of 45 or two family members of any age, then your risk of getting bowel cancer is higher than the general population. Certain types of bowel disease like Crohn’s disease or ulcerative colitis is also associated with bowel cancer, but only if the disease has damaged the lining of the bowel. More than 41,500 people are diagnosed with bowel cancer every year in the UK, and nearly 16,000 people will die of it (Bowel Cancer UK, 2015).
How diet affects bowel cancer
Whilst family history can be a strong predictor of bowel cancer, diet and lifestyle plays an important part in the development of many cancers, and it is well-acknowledged that bowel cancer could be prevented by changing diet and lifestyle. Cancer Research UK state that 1 in 10 bowel cancers are potentially linked to poor diet, but as research unfolds the link between cancer and diet, it’s possible that the proportion could be higher.
So let’s look at the components of our diet where we can make changes that could give us happy and healthy colons.
The World Health Organization (WHO) very recently advised that eating a lot of processed meats such as sausages, bacon, ham and pâtés is strongly linked to the causation of bowel cancer. Processed meats are those that have gone through preservation processing such as smoking, curing, adding preservative chemicals or using salting to give the meat its distinctive flavouring and texture. These types of meats can range from the economy or value sausages you can buy in bulk to the artisan and luxury ranges of meats that you might find in an Italian deli. The quality of the product does not make any difference, and so spending a lot of money on high-end produce doesn’t change the risk, because the link is not with the meat itself, but the process by which it goes through to produce the final result. However, this doesn’t mean that you need to exclude these types of foods from your diet completely, there are recommended health limits set, which currently stands at 70g of any processed food per day.
You might have heard that red meat can also be unhealthy (red meat includes beef, venison, lamb, veal, pork, mutton and goat). WHO did state that red meat has a probable, but not so strong, link to bowel cancer. The British guidelines for red meat have remained the same as those for processed meat, and did not change in light of the findings from WHO. It will be difficult for most people to stick to 70g of red or processed meat daily (that is, 70g in total, not 70g each), but there is a compromise. If you eat more than 90g, then ensure your daily average over that week is less than 70g a day and the easiest way to achieve this is have meat-free days. The thought of going vegetarian for most people is probably a step too far, but having two or even one totally vegetarian day a week is a great way to balance your diet. Many people now follow what has become known as “meat-free Mondays”. You could also consider substituting read and processed meats for poultry such as chicken, turkey, and duck and eat more fish (at least one serving per week should be oily fish) or even consider rabbit instead of red or processed meats.
How we prepare our food for the table can make a big difference too. Some people prefer their red meats quite rare or to retain a pinkish colour, others like it very well done and even “cremated” or black. During the summer, it is very popular to fire up the barbeque and smoke a few burgers and sausages. Burning meat or smoking it over the barbeque changes the molecular properties of meat and creates compounds that are carcinogenic (cancer-forming). You can offset some of the barbequing damage in meat by marinating it in dark beer before you grill it, but burning meat is non-negotiable: there aren’t any tricks to protect you from that.
Consuming too much sugar may have a link with bowel cancer, although studies on this particular area of nutrition are not conclusive. Some studies found an increased risk of overconsuming sugar with cancers of the large intestine and so the World Cancer Research Fund and the American Institute for Cancer Research have placed sugar as a “possible cause of bowel cancer”, and therefore it is probably safer to limit processed foods such as ready meals, premade sauces, ketchups, sugary desserts and sweets.
The messages around fat have been very confusing of late, and it’s very disappointing to see articles written by various people suggesting that saturated fat is not as unhealthy as once thought and it’s ok to eat animal fat. Not only OK, but beneficial. The focus on these articles is the link between saturated fat and heart disease, and all other links with saturated fat have been ignored. This has become very good news for producers of tropical oils, particularly coconut fat. Supermarket shelves are stocking up, advertisements showing usage of coconut fat in product development is increasing, and magazines are full of the wonders of this “superfood”. The fact is, there is no credible evidence that saturated fats in coconut (of which feature more highly than butter!) are in any way healthy (unless you smear it on your skin, then there’s pretty good evidence). The message “eat fat to stay thin” is totally ignoring the fact that high fat diets are linked to bowel cancer.
The only good scientific evidence around fats and oils focusses on essential fats. These are fats our body is unable to make itself and we must get from our diet. These are known as monounsaturated and polyunsaturated fats that you find in nuts, seeds, olives, avocado and fish. Nutritionists usually advise that you do your cooking in rapeseed or peanut (groundnut) oil and dress with olive oil, but you could dress with any nut oil that you enjoy. It’s better to go for cold-pressed extra virgin oils, because they face much less processing and have higher tolerance to heat. Overheating oils beyond their smoke point (the point to which they start to produce smoke) creates carcinogenic compounds called aldehydes and denatures them (breaks them down), and reheating oils lowers the smoke point, so they will convert to these compounds quicker. However, the positive note on this is that most domestic cooking techniques doesn’t give the sufficient time or heat to create these compounds, unless we repeatedly reuse oil or don’t turn the gas down; but chip shops may well produce high levels of aldehydes in their commercial fryers. Oils are also susceptible to oxidation when exposed to heat and light, so keep all oils in an airtight, sealed bottle or jar and store in a cool, dark cupboard (not the fridge).
According to Cancer Research UK, about 11% of all bowel cancers are caused by excess alcohol in the UK. The more you drink, the greater the risk and this risk grows proportionately: for every 2 units drunk per day (about one pint of beer or a large glass of wine), the risk of bowel cancer increases by around 9%.
The UK Government guidelines for alcohol are 14 units per week for both men and women, spread evenly across the week. 14 units are 6 glasses of wine or 6 pints of beer on average. For more information on alcohol and cancer, visit the DrinkAware website
Being physically active is linked to lower risks of breast, womb and bowel cancer. The largest studies conducted have shown that being physically active can reduce the risk of colon (but not rectal) cancer by up to 25%, which is a pretty impressive. It is also important to maintain a healthy weight, as being overweight is correlated with many cancer risks, not just bowel and rectal cancers. Exactly why exercise keeps down cancer risks isn’t entirely known. Exercise does keep our body fat levels down, which could be one link, but it also releases a number of hormones (and neurotransmitters) and stabilises others (such as insulin, the hormone responsible for taking sugar out of our blood and into cells – but it also tells some cells to replicate, that would also include cancer cells!). One infamous neurotransmitter that physical activity releases is endorphins, and these can help keep stress at bay. Stress can interfere with our immune system and therefore our ability to keep our cells healthy.
Exercise also helps keep bowels healthy by ensuring that food passes through at a proper rate, and this reduces the time that certain types of food like meat has contact with the bowel wall. It is this contact that predisposes us to cancer risk, because it damages the sensitive lining.
The UK Government guidelines for physical activity in adults (aged 19-64) are: aim for 150 minutes of moderate intensity activity per week in bouts of 10 minutes of more or 75 minutes of vigorous intensity exercise per week. It is also recommended that strength training exercises are undertaken at least twice a week, and where possible to avoid sedentary behaviour. For more information, download this factsheet:
The role of vitamin D and our immune system is really only just coming into its own. Research is showing that maintaining good levels of vitamin D all year round appears to be protective of certain types of diseases, and bowel cancer is one of them. Most of us can get adequate vitamin D simply be getting some daily sun light for around 15 minutes a day (without sun protecting cream). This is more difficult in the winter because of cloud cover and the fact that we need to wrap up when outside temperatures drop! But vitamin D can be found in some foods such as fish and dairy products, as well as vitamin D fortified foods like breakfast cereal and, increasingly, bread! Many milk substitutes like almond milk or soy milk are often fortified for vitamin D as well so exploring different foods is never a bad thing.
Vitamin D deficiency is now becoming much more widespread than previously thought, and doctors are slowly accepting this fact, and now offering tests to some patients. This practice is far from widespread though, so you’re best having an awareness of what your likelihood of a deficiency is. If any of the following apply to you, consider topping up your vitamin D with supplements:
* You have very dark skin
* You habitually cover your skin up for cultural reasons
* You work shift hours meaning you often do not see much daylight
* You spend a lot of time indoors during daylight hours
* You are vegan or a strict vegetarian (do not eat eggs or dairy).
Fibre and gut bacteria
We have millions of microbes living in our bowels, and it’s often a quoted fact that we have more bacteria living on and inside us that we have human cells. In a sense, we are more bacteria than we are human! In the last ten years, research in the types of bacteria that live in our bowel and the functions they have has grown exponentially. We now know that the type and behaviour of bacteria that live with us is highly influenced by our diet and therefore are very sensitive to any changes in our diet. In fact, so sensitive that you could see a complete change in their behaviour within two weeks of a diet change. One of the most exciting discoveries among all this research is how these bacteria influence the development of bowel cancer – bacteria produce compounds called “butyrate” from fermenting carbohydrates, which are proving to be protective against cancer as they are acidic in nature and therefore reduce the populations of “bad bacteria”, butyrate also has protective properties promoting the health of the gut lining and therefore, people with diets higher in dietary fibre and lower in fat will have less of these bowel polyps that, in time, can become cancerous. Friendly gut bacteria particularly like carbohydrates found in leeks, asparagus, onions, garlic, artichokes and wholegrains. Eating fermented foods may also be beneficial if you eat them very regularly: kimchi (pickled vegetables), sauerkraut, yoghurts and fermented milks (usually sold as “shots” like Yakult or as kefir found in the Polish section of supermarket fridges) are all foods that are associated with better gut health. Many British people find the idea of these foods quite unappealing but they are very popular in Eastern Europe and East Asia.
Seb is a writer and blogger of food and nutrition. He holds a bachelors and a masters degree in nutrition science, and has studied sports and exercise nutrition at postgraduate level. He specialises in plant-based nutrition and believes passionately that we can all live with a little less meat.