Eat to beat, or prevent, bowel cancer

Especially if you have IBD colitis or Crohn’s

If you're living with inflammatory bowel disease, whether ulcerative colitis or Crohn’s disease affecting the colon, it's important to know that your long-term risk of bowel cancer is higher than average. This is due to the chronic inflammation that can affect the bowel lining over time, especially if the disease has been widespread, long-standing or poorly controlled.

For some people, this risk is further increased by the presence of polyps (adenomas) or a family history of colorectal cancer. But there is also good news. Diet can play a key role in supporting the health of your bowel and may help reduce your risk of further problems.

In this blog, I’ll walk through the nutrients and foods that research suggests are helpful, the possible mechanisms behind them, and which foods are best limited or avoided altogether. 

A Mediterranean-style, mostly plant-based diet offers an excellent framework and includes most of the protective foods listed below. Even if you’re in a flare, and not yet able to tolerate everything, small steps in the right direction can begin to move your health in a positive direction.

Fibre from real food

One of the most consistent findings in bowel cancer research is the protective effect of fibre. In IBD, this needs to be balanced carefully depending on your current symptoms, but when tolerated, fibre helps keep the digestive system working smoothly by increasing stool bulk and speeding up transit time. This reduces contact between waste products and the bowel lining. Fibre also binds substances like bile acids that can irritate the colon.

It supports a healthy microbiome, encouraging beneficial bacteria that produce compounds such as butyrate. Butyrate helps maintain the health of the colon lining and has anti-inflammatory effects.

Best sources of fibre include beans and pulses, wholegrains such as oats, vegetables, fruit, flax and other seeds. During a flare, soft or soluble fibres may be better tolerated, such as oats, peeled and cooked vegetables or puréed soups. Fibre supplements do not appear to offer the same protection as real food, and a varied intake of natural plant foods is preferable.

Some people with IBD also find that adding psyllium husk helps support regularity and comfort once symptoms are under control. Psyllium is a soluble fibre that forms a gentle gel in the bowel, helping to bulk and soften stool. Start with a small amount and increase gradually, as it may not suit everyone during active flares.

It has been shown to help maintain remission in ulcerative colitis. In one study, psyllium was found to be as effective as mesalazine, a commonly prescribed anti-inflammatory drug, and combining the two improved outcomes further (Fernández-Bañares et al., Am J Clin Nutr, 1999). 

Calcium

Calcium has been shown to help reduce the recurrence of polyps because it also binds to bile acids in the colon. It plays a role in regulating cell division and supporting proper cellular repair, both of which are important when inflammation is present.

Calcium is plentiful in dairy such as milk, yoghurt and cheese. For those who don’t tolerate dairy, good sources include dark green leafy vegetables, almonds, tofu set with calcium, and fortified plant milks. If using the latter, check the label and avoid those containing dietary emulsifiers such as carboxymethylcellulose (CMC) or polysorbate-80, as these additives have been associated with increased intestinal permeability and may contribute to gut inflammation in people with IBD. 

Aim for 1000 to 1200 mg per day, ideally from food (the recommended daily amount for adults is around 1000 mg). If you are considering supplements, speak to a nutritional practitioner like me, as you may need a higher or lower dose depending on your age, medication use or overall health.

The Calcium Polyp Prevention Study found a 20 percent reduction in the recurrence of polyps among people who had previously had them removed and took 1200 mg of calcium daily.

Vitamin D

Vitamin D works alongside calcium and plays a role in immune regulation and controlling how cells grow and die. Low levels of vitamin D have been associated with an increased risk of colorectal cancer, and many people with IBD are deficient, especially in the winter or during periods of gut inflammation.

Your doctor can do a simple test to check your level. Sunlight is the main source, but mushrooms, fortified foods and appropriate supplements can help. Combining vitamin D with calcium may be more effective than calcium alone.

Cruciferous vegetables

Cruciferous vegetables (also known as brassicas) such as broccoli, kale, Brussels sprouts, cauliflower and cabbage are rich in compounds called glucosinolates. When chewed, these turn into isothiocyanates and indoles, which help support the liver’s detoxification pathways and may reduce the growth of abnormal cells in the colon.

If you're flaring or sensitive to roughage, these may be easier to tolerate when well-cooked or blended. Raw, stir-fried or lightly cooked is ideal for those who tolerate them well. Try to include them several times a week, even in small portions.

Garlic and onions

Members of the allium family, such as garlic, onions, leeks and shallots, contain sulphur-rich compounds that have been studied for their potential to reduce the risk of various cancers, including bowel cancer. These compounds can inhibit inflammation, support immune function and may help the body block cancer-promoting processes.

If raw garlic or onion triggers symptoms, cooking them thoroughly or using garlic oil instead can be a gentler option. These foods also help feed beneficial gut bacteria and may support microbial diversity over time.

Resistant starch

Resistant starch is a type of fibre that is not digested in the small intestine but ferments in the colon, feeding bacteria that produce short-chain fatty acids. These include butyrate, which has anti-inflammatory and protective effects on the bowel lining.

Good sources include cooked and cooled potatoes, pasta or rice, green bananas, lentils, peas and oats. These foods can often be tolerated when well prepared. During a flare, it may help to mash, blend or soften them. The CAPP2 trial found that resistant starch reduced the incidence of certain types of cancer in people with Lynch syndrome, a genetic condition that increases bowel cancer risk.

IBD and plant sensitivity

Some people with IBD are sensitive to certain fibres or plant foods, particularly during flares. This can be due to a variety of factors, including imbalanced gut bacteria, low butyrate production, increased gut permeability or previous dietary restriction, which can all affect tolerance. If this is the case for you, it’s worth working with a nutritional therapist who understands the various causes of plant fibre intolerance in IBD clients, like me. If you're working alone, try starting with softer, more soluble fibres like oats, peeled and cooked vegetables, stewed fruits or blended lentils, and introduce one food at a time in small amounts. Keep a food and symptom journal, eat slowly and chew thoroughly. Over time, the gut can often adapt to a more diverse, fibre-rich diet as inflammation settles and microbial balance improves.

Omega-3 fatty acids

Omega-3s, particularly EPA and DHA, have anti-inflammatory properties that may be helpful in reducing bowel cancer risk and supporting immune balance in people with IBD. While the evidence is still emerging, several studies have shown promising links between higher omega-3 intake and reduced colorectal cancer incidence.

Oily fish such as sardines, salmon and mackerel are the richest dietary sources if you include fish in your diet. Plant-based sources include flaxseed, chia seeds, walnuts and algae-based supplements.

Foods that increase risk

Processed meat

There is strong evidence that processed meats increase the risk of bowel cancer. This includes bacon, sausages, ham, salami and other cured or smoked meats. The World Health Organization has classified processed meat as a Group 1 carcinogen, meaning it is known to cause cancer in humans. Even small amounts eaten regularly can increase risk.

Red meat

Red meat, especially when grilled, barbecued or fried at high temperatures, is also linked with a higher risk. Cooking methods that char or blacken meat can form carcinogenic compounds called Advanced Glycated End Products or AGEs. If you choose to eat red meat, aim to keep it below around two to three modest servings per week and choose stewing, baking or steaming rather than frying or grilling.

Alcohol

Alcohol intake is also linked with bowel cancer. The risk increases with the amount consumed. The safest approach is to drink very little or not at all, particularly if you have IBD. Alcohol can also increase gut permeability, irritate the bowel lining and disrupt the microbiome.

Final thoughts – let food be thy medicine

Food is one of the most powerful tools we have to support long-term digestive health. A diet rich in fibre, nutrients and natural protective compounds can help create the conditions in which the gut can thrive. For people with IBD, supporting the microbiome and reducing inflammation through food may be especially important.

Now is a good time to review your diet, look at where you can add more protective foods, and reduce exposure to the foods known to increase risk. Even gentle, gradual changes can make a meaningful difference.

If you’d like support moving towards a way of eating that feels realistic and nourishing for where you are right now, feel free to message me or explore my programme designed specifically for people with IBD.

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For me to do:

Facebook post to point to this blog

🔎 Did you know people with IBD have a higher long-term risk of bowel cancer?

Whether you have ulcerative colitis or Crohn’s affecting the colon, chronic inflammation can increase the likelihood of changes to the bowel lining over time.

The good news is, your diet can make a real difference.

In my latest blog, I share the key foods and nutrients that research suggests may help reduce bowel cancer risk in people with IBD, along with what to avoid or limit, and why a Mediterranean-style diet can be a smart move.

🌿 It’s not about perfection but it’s about gentle progress.

Read the full blog here: [insert blog link]