Bowel Cancer: Tips to significantly reduce risk of disease according to oncologist Professor Robert Thomas

The trouble is, young people, first notice problems with frank blood in the stool, colicky pain or even bowel blockage caused by larger cancers. On the other hand, older people's bowel cancers are increasingly being picked up, early, through screening. Despite medical advances, the chance of surviving bowel cancer very much depends on the stage, how advanced it is, at presentation.

Although a minority of people have a genetic susceptibility to bowel cancer, official figures from Cancer Research UK report that over half of bowel cancers can be prevented through lifestyle choices. I believe this figure could be even higher if considering the latest data for gut health, vitamin D and diet.

So what are the most important things we can do, or advise our teenagers to do, to avoid the risk of bowel cancer which is prematurely killing 17,000 people each year in the UK alone?

Physical activity

Regular exercise has been linked to, at least, a 30% lower risk of bowel cancer in several large robust studies. Exercise promotes bowel motility, which reduces the time that harmful waste products such as carcinogens spend in the colon. It reduces excess inflammation and at the same time strengthens the immune system so the body can identify early cancer cells and kill them.

The American Cancer Society recommends 150 minutes of moderate-intensity exercise or 75 minutes of vigorous-intensity exercise per week for a preventative benefit.

Avoid sedentary behaviour

Even if you go to the gym or work out twice a week but then sit around doing nothing the rest of the time, that's just as bad. It's important to avoid long periods of not moving such as sitting at a desk, watching TV or playing video games.

This association was demonstrated in a study involving 90,000 nurses, aged between 25–42 years followed for over 15 years. Those who watched TV for more than 7 hours a week had a much higher cancer risk compared to those lounging around for less than hours.

Fruit, vegetables, grains, legumes, herbs, and spices

Whole grains such as wheat, whole rice, corn, barley, and oats are rich in fibre, vitamins, minerals, and other cancer-protective micronutrients. Refining grains to make white flour and rice removes the germ and outer fibre, reducing the health benefits, so try to eat foods that use the whole grain. The drawback is gluten intolerance, especially as we get older. Switching to sourdough bread and soaking grains overnight can help reduce gluten in wheat and other similar proteins found in oats.

Pulses (legumes) and seeds such as beans, lentils, pumpkin seeds and peanuts are great sources of dietary fibre and essential nutrients. They also help the growth of healthy bacteria in the gut by acting as prebiotics. The same applies to mushrooms, artichokes, garlic, and other allium vegetables such as leeks and onions.

Non-starchy vegetables are particularly good for bowel health, and these include carrots, beets, leafy green vegetables such as spinach and lettuce; cruciferous vegetables such as broccoli, asparagus, and watercress.

Fruit, including virtually all edible berries and citrus varieties, are excellent sources of vitamin C, fibre, and minerals. Much of the fibre and healthy phytochemicals are found in the pulp that runs through the whole fruit, so squeezing and drinking the juice will only give half the nutrients. Juicing also significantly increases the sugar content, which negates some of the benefits. So, as they say in California, "eat your fruit and juice your vegetables."

Herbs and spices are rich in natural chemicals called phytochemicals which provide the colour, aroma and taste but also have enormous health benefits including the prevention of bowel cancer. Phytochemicals are abundant in Asian and Mediterranean diets but the typical western diet are dreadfully deficient, meaning we need to eat a lot more of them.

Ongoing studies are investigating whether boosting these foods in supplement form could enhance their health properties but in the meantime, we should aim to have one or more vegetable, fruit or other phytochemical rich food with every meal of the day.

Nuts are a high-quality vegetable protein, have unsaturated fatty acids, fibre, vitamins, and essential minerals such as zinc, potassium, calcium and magnesium. Not a surprise then that well-conducted studies have shown that eating a handful of nuts such as almonds, walnuts, hazelnuts, and brazils more than three times a week reduces the risk of heart disease, diabetes, and bowel cancer by up to 25%.

Excess meat and processed meat

Excess meat intake major contributor to human disease and it is a well-established fact that cancer rates are lower among vegetarians. There are, of course, some benefits to eating some meat, as it is an easily absorbable source of protein, a good source of vitamin B12 and if it comes from an animal that has been reared on grass and is free-range, is a good source of omega 3. Young women with periods who are at a higher risk of iron deficiency would benefit from some meat in their diets.

On the bright side, studies suggest that meat eaters who also had a high intake of vegetables, fruit, whole grains and spices only had a moderately increased risk, whereas it was the salad-dodging carnivores who had a particularly high risk. It’s not just the quantity of meat that matters, but also the quality, and how it is preserved and cooked. Processed meats such as many sausages, bacon, sliced ham and all tinned meats are the main culprits.

The European Prospective Investigation into Cancer (EPIC) study reported a strong link between red meat intake and colon cancer. A combined analysis of prospective studies concluded that people who eat processed meat most days were 30% more likely to die prematurely and 22% more likely to die of bowel cancer.

Processed meats are often high in nitrates, other preservatives, and even sugar. In 2018, one of the largest and well conducted studies in the UK called the UK biobank study found that processed-meat intake (equivalent to two sausages a week) was linked to an increased risk of bowel as well as breast cancer.

Although nitrates in plants are healthy, nitrites in meat combine with the protein in the meat to form substances called nitrosamines, and these are the real bad guys which damage our DNA, causing cancerous mutations. The harm from nitrates in meat can be somewhat counterbalanced by eating plenty of phytochemical-rich herbs, spices, and vegetables with them as this converts them to healthy Nitric oxide rather than nitrosamines.

This was eloquently demonstrated by a barbecue-loving researcher from the University of Arkansas in the US. His study showed that the level of nitrosamines in the bloodstream of consumers was significantly lower if meat had been marinated in rosemary, oregano, or parsley before cooking. So, make sure to include some tomatoes and spinach with your cooked breakfast.

Other factors that affect nitrosamine formation are the amount of healthy bacteria present in the gut as they block the formation of nitrosamines. Conversely, harmful bacteria such as Helicobacter pylori can create an environment conducive to nitrosamine formation, which may explain why chronic overgrowth of this bacteria increases the risk of cancer.

Considering all these factors, eating less meat would have considerable health and also help the environment. That said, many people like the taste of meat and feel their lives are less fulfilled without it and evidence suggests that eating meat up to three times a week is safe. If you are a carnivore, it may be worth going for quality not quantity and try to limit consumption to 2-3 times a week and eating plenty of herbs, spices and vegetables with every meal.

Gum and dental hygiene

Several studies including a recent Canadian analysis published in 2022 found that people with gum disease had one and a half times increased risk of bowel cancer. Gum disease increases the whole body inflammation, which promotes cancer and trials have found the same inflammation promoting bacteria from the gums imbedded in the cancers in the colon indicating a direct mechanism for cancer formation.

Excess Alcohol intake

Moderate to heavy alcohol consumption (>2 drinks a day) increases the risk of bowel cancer but people with a genetic susceptibility to alcohol common in Asian countries, may be more vulnerable to lower amounts. Regular alcohol intake contributes to weight gain and lower mood and motivation to exercise.

Ethanol metabolism generates acetaldehyde and acetate which have carcinogenic properties. More recently it has been discovered that alcohol can disrupt the balance of healthy to unhealthy bacteria. The effect is less with low quantities of red wine as it contains a healthy polyphenol called resveratrol which in a study from Kings College London was shown to actually help the growth of anti-cancer gut bacteria.

Healthy gut bacteria

Many studies have linked poor gut flora with a higher risk of bowel cancer. Unhealthy bacteria encourages the formation of damaging nitrosamines from nitrates in meat. Having poor gut health also creates inflammation in the gut lining cells which then divide faster. More rapidly dividing cells are more likely to develop spontaneous mutations of DNA and have less time for them to repair themselves. On top of this, the areas in the gut which generate the immune cells, shrink so there is a lower chance that the local immune system will recognise the early cancer cells and kill them. Lots of factors affect the health of the gut from exercise, smoking diet, weight gain and stress.

Smoking and smoked foods

People associate smoking with lung cancer but smokers have a 10% increased risk of bowel cancer and this increases with the number of cigarettes smoked per day. Smokers are also more likely to develop polyps which could turn into cancer if not discovered. If you smoke, try to explore strategies to help you quit and make sure you participate in regular bowel screening.

Smoke can also be ingested by food. This can explain why Hungary and Slovenian, which have a tradition of home smoking meat, have the highest rate of bowel and also stomach cancer.

Maintaining high normal vitamin D levels

A number of studies have firmly established that higher blood vitamin D levels are linked to a lower risk of bowel cancer. Interestingly the best protection was from levels over 75-100 nmol/L. The majority of people in Northern climates have levels significantly lower than this, especially in the Winter. Regular, sun exposure (without burning) is the best way to maintain vitamin D levels but this is impractical for most people throughout the year. Vitamin D supplementation especially if combined with a probiotic which enhances its effect does seem a sensible approach to maintaining these levels.

Calcium and Dairy Products

Milk has received a bad reputation over the years, but several studies consistently show that people who consume milk have a lower risk of bowel cancer. The challenge is that milk, cream, and cheese can be fattening, increasing the risks, so use them in moderation.

Additionally, many of us are lactose intolerant, especially as we age, which can cause digestive problems. Mature cheeses like parmesan and live yogurts have most of the lactose fermented, making them more tolerable to consume. Other plant-based milks, such as soy and almond milk, are also rich in calcium, considered the main protective element.

Being Overweight or Obese

Being overweight or obese and carrying excess weight around your waist can increase your risk of bowel cancer by at least 10%. The reasons why obesity contributes to the risk of bowel cancer are multifactorial, including associations with reduced exercise levels, poorer diets, and suboptimal gut health.

In conclusion, it is inevitable that most foods and lifestyle habits will contain some harmful elements, but you have to consider the overall picture. The concentration of toxins and the accumulation of bad habits over time are what matter. Your body can certainly cope with the occasional unhealthy meal, but consuming foods containing toxins without the healthy antidotes every day will strain it, especially when combined with a sedentary lifestyle, being overweight or smoking.