A flexible sigmoidoscopy allows a doctor to examine the lower large intestine, specifically the rectum and the sigmoid colon. This examination uses a thin, flexible tube equipped with a light and a camera to look for issues such as polyps, inflammation, or the cause of bleeding. To ensure the procedure is safe and accurate, the lower bowel must be completely clear of stool, requiring a precise preparation regimen.
The Initial Dietary Restriction Timeline
The preparation for a sigmoidoscopy often begins with dietary changes several days before the scheduled procedure time. Healthcare providers typically recommend switching to a low-fiber diet about two to three days prior to the exam. This initial step helps to reduce the amount of indigestible residue that can cling to the colon walls, which makes the final cleansing steps more effective. Low-fiber foods include items like white bread, white rice, and well-cooked vegetables without skins or seeds.
The final cut-off time for all solid food is usually 24 hours before the procedure or at midnight the night before. From this point onward, you must only consume clear liquids, a transition that is sometimes coupled with the use of oral laxatives. Strict adherence to this timing is necessary because any remaining solid matter in the sigmoid colon can obscure the doctor’s view, potentially leading to missed findings or the need to reschedule the examination. While a common guideline is 24 hours, you must always follow the exact timeline provided by your individual healthcare facility, as protocols can vary slightly.
Guidelines for the Clear Liquid Diet
Once solid food is restricted, the next phase involves a clear liquid diet that continues until a few hours before the procedure. A clear liquid is defined as any liquid you can see through, which ensures that nothing leaves solid residue in the digestive tract. Permitted items include:
- Water
- Plain gelatin
- Clear broth (chicken or beef)
- Apple juice without pulp
- Sports drinks
Avoid any liquids or gelatin that are red or purple in color, as these dyes can stain the colon lining and may be mistaken for blood during the examination. You should also not consume milk, alcohol, or any juices that contain pulp. This phase of the diet is designed to keep you hydrated and provide some calories while actively flushing the lower colon. Drinking extra clear liquids is important to prevent dehydration during the cleansing process.
The final restriction involves stopping all liquid intake, including water, which usually occurs two to four hours before the scheduled check-in time. This final cut-off is a safety measure, especially if you are receiving sedation for the procedure. Having an empty stomach reduces the risk of pulmonary aspiration—where stomach contents are inhaled into the lungs—should you vomit while sedated. You may still be allowed a small sip of water to take necessary medications during this final window, but you must confirm this with your provider.
Necessary Bowel Cleansing Steps
Dietary adjustments alone are often insufficient to achieve the level of cleanliness required for a successful sigmoidoscopy. The lower colon must be thoroughly emptied, which is usually accomplished through the use of a prescription oral laxative or, more commonly for this specific procedure, a ready-to-use enema kit. The goal is for the final stool output to be a clear or yellow liquid, indicating that the colon walls are fully visible.
If an oral laxative is prescribed, such as Magnesium Citrate, it is typically consumed the evening before the exam to induce a series of watery bowel movements. For many sigmoidoscopies, however, the preparation involves administering one or two over-the-counter Fleet enemas. These enemas are usually administered rectally one to two hours before leaving home for the appointment or shortly before the procedure at the facility.
The enema fluid works by drawing water into the colon to soften stool and mechanically stimulating the bowel to contract and expel its contents. Following the directions precisely, including the waiting time between the first and second enema, is vital for a clear result. If the expelled fluid is not clear after the prescribed enemas, a third may sometimes be necessary, as directed by your physician’s instructions.
Adjusting Medications and Supplements
Beyond managing food and liquid intake, patients must also review their current medications and supplements with their prescribing physician well in advance of the procedure. Several common medications can introduce risks or interfere with the clarity of the examination. This review is separate from the dietary restrictions but just as important for patient safety and diagnostic accuracy.
Blood Thinners and Iron
Blood thinners, or anticoagulants, such as warfarin, clopidogrel, or apixaban, are a primary concern because they increase the risk of bleeding if a biopsy is taken or a polyp is removed. Depending on the specific drug and the patient’s medical history, the doctor may instruct the patient to stop taking the medication for a period ranging from one to seven days before the procedure. Iron supplements and vitamins containing iron must also be stopped, often five to seven days before the exam, because iron residue can leave a dark stain on the lining of the colon that can be mistaken for a serious condition.
Diabetes Medications
Patients with diabetes must carefully coordinate their medication schedule, including insulin and oral agents like metformin, with their doctor due to the strict reduction in food intake. Not eating solid food can significantly lower blood sugar levels, necessitating a temporary reduction or omission of medication doses to prevent hypoglycemia. Newer diabetes and weight-loss medications, such as GLP-1 agonists (e.g., semaglutide), may also need to be stopped a week or more prior to the procedure due to their effect on stomach emptying. Any changes to prescription medications must only be made under the direct guidance of the prescribing healthcare provider.