Diet, Colorectal Cancer Prevention and Eating During Treatment

Risk rises with age, family history, inflammatory bowel disease and inherited conditions. Lifestyle factors that raise risk include excess body fat, alcohol, smoking, a diet high in red and processed meat, low fibre and little physical activity. Factors linked to lower risk include whole grains, fibre, dairy products and calcium, and regular activity. Many of these links come from observational studies; they show association, not proof that changing one food will prevent cancer in any one person.

Colorectal cancer is one of the most common cancers worldwide and is among the most frequent cancers in Saudi Arabia, and it is being diagnosed at younger ages in many countries. Studies estimate that a considerable share of cases is linked to modifiable factors such as diet, weight, alcohol, smoking and inactivity.

Colorectal cancer is among the most common cancers in the Kingdom, and the Ministry of Health promotes early detection and screening; ask your primary care clinic about the national programme and when to start. Traditional meals often centre on white rice and meat (kabsa, mandi, grilled meat), so a practical change is to serve more salad, vegetables and legumes, use brown or part-brown rice, grill rather than deep-fry, and keep red meat portions smaller, with fish and chicken more often. Limit processed meats and sweetened drinks. In Ramadan, if you are on treatment, have lost weight, are on chemotherapy or have a stoma, speak to your oncology team before deciding to fast; the religion provides for exemption in illness.

Diagnosis is made by colonoscopy with biopsy, followed by CT, MRI and blood tests to see the extent of the disease. For people without symptoms, screening (stool tests, colonoscopy) finds polyps and early cancer; ask your doctor when to begin, as people with a family history or inflammatory bowel disease may need to start earlier. Before and during treatment a dietitian screens for weight loss, poor intake and muscle loss, which are common and affect treatment outcomes.

These habits lower risk and support treatment and recovery.

• Get screened when it is due; screening is the single most effective way to prevent bowel cancer or catch it early.

• Aim for a healthy weight and avoid weight gain around the waist.

• Be active: at least 150 minutes of moderate activity a week is advised for adults, and during treatment move as much as you safely can.

• Do not smoke (including shisha) and avoid alcohol.

• During treatment, weigh yourself weekly and tell your team about weight loss early.

The advice differs between prevention and treatment. Do the first now if you are well; follow the second if you are being treated, with your dietitian.

• Prevention: build meals around vegetables, fruit, legumes (lentils, chickpeas, ful), nuts and whole grains (oats, whole wheat bread, brown rice, bulgur, freekeh). Aim for roughly 30 grams of fibre a day; each extra 10 grams of daily fibre was linked to a roughly 10% lower risk in pooled studies.

• Prevention: keep red meat (beef, lamb, camel, goat) modest, around 350 to 500 grams cooked weight a week at most, and avoid processed meats such as sausages, luncheon meat and cured meats as far as possible; eat more fish, poultry and legumes.

• Prevention: limit sugary drinks, sweets, fried and ultra-processed foods; they add calories and weight without nutrition. Avoid alcohol.

• Prevention: dairy foods such as laban and yoghurt can be included; do not rely on supplements, and discuss any vitamin D or calcium pills with your doctor.

• Treatment: eat enough. Food is part of treatment. Eat small, frequent, high-energy and high-protein meals and snacks (eggs, fish, chicken, yoghurt, labneh, hummus, nut butters, milk, dates with nuts). Weight loss during treatment is not something to celebrate.

• Before surgery: your team may advise eating normally until the permitted time, a carbohydrate drink before surgery, and nutrition drinks if you are underweight. After surgery, eating again early is encouraged as part of enhanced recovery programmes.

• Chemotherapy side effects: for nausea, try small dry or cold bland foods and ginger; for mouth sores, soft, moist, non-spicy, non-acidic foods; for diarrhoea, drink plenty of fluids, eat small portions and limit very fatty, sugary or caffeinated items and sugar alcohols; for constipation, fluids and gentle fibre; ask your team about any drug-specific advice (for example, some regimens make cold food and drinks painful to swallow for a few days after treatment).

• With a new colostomy or ileostomy: reintroduce foods gradually, chew well, drink plenty of fluids, and ask your stoma nurse about foods that cause gas, odour or blockage (for example nuts, corn, mushrooms and skins in large amounts).

• Food safety matters when your immunity is low: wash hands, cook meat and eggs well, wash produce, avoid unpasteurised milk and cheeses and raw fish. A very restrictive neutropenic diet is not shown to be better than good food safety.

• Be cautious with supplements: antioxidants, herbal products and “immune boosters” can interfere with treatment or the liver. Tell your oncology team about everything you take.

Be wary of claims that sugar-free, fasting, juice-only or “alkaline” diets cure or starve cancer. There is no good evidence for them, and they can cause dangerous weight loss.

Cancer treatment is decided by your oncology team. Medicines also support eating.

• Chemotherapy, targeted therapy and immunotherapy are chosen according to the stage and tumour tests.

• Anti-sickness medicines before and after chemotherapy can greatly improve eating; take them as prescribed rather than waiting until you feel sick.

• Anti-diarrhoea medicines, mouth care, appetite support and pain relief are available; ask early.

• Iron, vitamin or electrolyte replacement is given if tests show a deficiency, sometimes by drip.

• Oral nutrition supplement drinks can be prescribed when food is not enough.

Procedures find polyps early, treat the cancer, and support nutrition.

• Colonoscopy finds and removes polyps (polypectomy), which prevents many cancers.

• Surgery to remove the tumour and nearby lymph nodes is the main treatment for many bowel cancers; some patients have a temporary or permanent stoma.

• Radiotherapy (especially for rectal cancer) can cause diarrhoea and bowel irritation, for which dietitian advice helps.

• A feeding tube or intravenous nutrition is sometimes used for a time when eating is not possible.

The World Cancer Research Fund / American Institute for Cancer Research Continuous Update Project (2018) judged that wholegrains and foods containing fibre, and dairy products probably lower colorectal cancer risk, while red meat, processed meat, alcohol, and body fatness raise risk. The WHO’s International Agency for Research on Cancer classified processed meat as carcinogenic to humans and red meat as probably carcinogenic (2015); the increase in lifetime risk from a daily portion of processed meat is small in absolute terms but real. No supplement has been proven to prevent colorectal cancer, and high-dose supplements are not recommended. For survivors, the American Cancer Society (2020) guideline and observational studies suggest that exercise, a healthy weight and a diet rich in vegetables, fruit and whole grains with less red and processed meat are associated with better outcomes, but randomised trial proof is limited. During treatment, ESPEN guidelines for cancer patients (2021) advise screening for malnutrition early, aiming for about 25 to 30 kcal per kg of body weight daily and more than 1 g/kg of protein, keeping physically active, and using oral supplements or tube feeding when needed. They do not support restrictive “cancer diets”.

When found early, colorectal cancer is often curable, and screening greatly improves the chance of cure. Good nutrition and activity during and after treatment help recovery, energy and quality of life. Diet cannot replace surgery, chemotherapy, radiotherapy or other treatment your team recommends.

• When should I start screening, and which test is best for me?

• Can I see a dietitian before and during treatment?

• How many calories and how much protein do I need?

• How should I manage nausea, diarrhoea or mouth sores?

• Are any supplements or herbal products safe with my treatment?

This guide comes from the Saudi Gastroenterology Association (SGA) patient library, prepared by the Approved for publication by SGA; individual clinician review is ongoing. Last reviewed: 2026-04-24. It is for education and does not replace your doctor's advice.