Colonoscopy: what to eat before the exam

Why dietary preparation matters

Colonoscopy remains the reference standard for early detection of colorectal neoplasia, but its diagnostic yield depends heavily on the quality of bowel cleansing achieved before the procedure. Inadequate preparation is one of the leading reasons colonoscopies must be repeated, creating unnecessary burden for both patients and endoscopy units.

Yet colorectal cancer screening uptake remains suboptimal in many settings: in Italy, only 47% of the target population aged 50–69 completed a screening test within recommended intervals in 2023–2024, with participation ranging from 30% in southern regions to 62% in the north (source: PASSI surveillance, Italian National Institute of Health). Clear, accurate guidance on diet before colonoscopy can help reduce patient anxiety and improve adherence to screening pathways.

This article, intended for gastroenterologists, endoscopists, and healthcare professionals supporting patients during the pre-procedural phase, summarizes current recommendations on diet before colonoscopy, based on the most recent ESGE (European Society of Gastrointestinal Endoscopy) guidelines and indications shared by AIGO and SIED.

What to eat before a colonoscopy

2–3 Days Before: A Low-Residue Diet

The ESGE bowel preparation guideline (2019 update, endorsed by SIED) recommends, with a moderate level of evidence, a low-fiber diet in the 24–48 hours preceding the procedure, rather than a prolonged multi-day residue-free regimen. In routine Italian clinical practice, many endoscopy units nonetheless advise patients to begin reducing fiber intake 2–3 days in advance, particularly those with chronic constipation or slow intestinal transit.

Foods generally well tolerated during this phase include:

• white rice, pasta, and refined bread;
• lean meat and fish, cooked without excess fat;
• eggs;
• plain yogurt and fresh cheeses, in moderate amounts;
• filtered fruit juices without pulp;
• filtered vegetable or meat broth.

The Day Before: Clear Liquid Diet

In the 24 hours before the exam, alongside the bowel preparation solution (typically polyethylene glycol, PEG-based), patients should follow an exclusively clear liquid diet: water, light tea, chamomile, herbal infusions, filtered broth, and clear fruit juices, avoiding solid food entirely.

ESGE guidance also emphasizes that the interval between the last dose of bowel preparation and the start of the colonoscopy should be minimized, ideally not exceeding 4 hours, to achieve optimal bowel cleansing and mucosal visualization.

Hydration and Practical Tips

Adequate hydration in the days before the exam supports the action of the bowel preparation and reduces the risk of headache or hypotension during fasting. Patients should spread fluid intake throughout the day and, unless otherwise instructed, continue essential chronic medications (cardiac, antihypertensive, respiratory) with a small sip of water.

Foods to avoid before a colonoscopy

Certain foods and habits can compromise bowel preparation quality or interfere with endoscopic visualization of the mucosa:

• high-fiber, high-residue foods: legumes, whole grains, leafy vegetables, fruit with skin and seeds (kiwi, strawberries, grapes, figs);
• seeds and small grains (e.g., flax, sunflower, sesame), which may lodge in colonic folds;
• red or purple-colored foods and beverages (colored sodas, berry-flavored gelatin, beetroot), which can mimic blood traces during the exam;
• excessive dairy intake in the 24 hours before the procedure, due to potential laxative effects and mucosal residue;
• alcoholic beverages, which may interact with the sedation used during the procedure;
• fatty or fried foods, which digest more slowly.

Patients should also inform their physician of any ongoing therapies (anticoagulants, antiplatelet agents, oral iron), whose pre-procedural management follows specific ESGE recommendations and should never be modified independently.

Conclusion

Correct dietary habits in the days before a colonoscopy, combined with bowel preparation carried out according to the prescribing physician’s instructions, remain among the most determinant factors for exam quality and diagnostic reliability. Properly informing patients about what to eat and what to avoid before a colonoscopy helps achieve more accurate exams, fewer repeat procedures, and stronger adherence to colorectal cancer screening pathways.