Revisiting bowel preparation: The quest for the optimal low-residue diet duration

Colorectal cancer (CRC) ranks as the third most common cancer worldwide and the second leading cause of cancer-related deaths.¹ Timely CRC screening has been proven to reduce both CRC mortality and incidence.^2-4 Colonoscopy, a critical component of both stool-based and scope-based screening approaches, has a vital role in detecting and removing either cancerous or precancerous neoplasms. By doing so, it helps shield individuals from advanced CRC. Nonetheless, it is important to recognize that the protection offered by colonoscopy is not perfect. Post-colonoscopy CRC may still develop in some cases, highlighting the need for ongoing improvements in colonoscopy quality and adherence to screening guidelines.^{5, 6}

An audit on the quality of colonoscopy is a valuable practice that can help guarantee the effectiveness and safety of the procedure. Key quality indicators for colonoscopy include adequate bowel preparation, cecal intubation rate, withdrawal time, and adenoma detection rate. By assessing and monitoring key quality indicators, medical professionals can identify areas for improvement, implement necessary changes, and ensure that patients receive the highest standard of care during colonoscopy procedures.^{7, 8}

High-quality bowel preparation plays a crucial role in ensuring optimal outcomes during colonoscopy procedures. Inadequate bowel preparation is associated with lower rates of detecting neoplastic polyps, higher rates of incomplete procedures, and the need for more frequent repeat procedures. It is concerning that previous studies have indicated that up to 25% of colonoscopies have inadequate bowel preparation. This highlights the importance of conducting evaluations to assess the quality of bowel preparation and identify areas for improvement.⁹

Diet restriction and the use of appropriate cleansing agents are key steps in achieving optimal bowel preparation for colonoscopy. Low-residue diet (LRD) and clear liquid diet (CLD) are commonly used for bowel preparation. LRD allows the consumption of select low-fiber foods while excluding high-fiber foods, whereas CLD limits intake to clear liquids only. A meta-analysis of nine randomized controlled trials (RCTs) compared the two diets and found that LRD was associated with higher patient satisfaction, better tolerance, and more frequent consumption of bowel laxatives. However, there were no significant differences in terms of adequate bowel preparation or adenoma detection rate between the two groups.¹⁰ While the majority of academic societies recommend LRD for bowel preparation,^{9, 11} the decision between LRD and CLD should be based on individual needs and made in consultation with healthcare professionals.

The duration of diet restriction can pose challenges to bowel preparation as it may require significant dietary changes and adherence may be difficult for some patients. Recent RCTs have compared the effectiveness of a 1-day LRD versus a 3-day LRD for bowel preparation before colonoscopy. These RCTs have shown that a 1-day LRD is equally effective as a 3-day LRD in achieving adequate bowel cleansing. Moreover, the shorter duration of the 1-day LRD was better tolerated by patients. These findings suggest that a 1-day LRD may be a more practical and patient friendly approach for bowel preparation.^{12, 13} Nonetheless, the optimal duration of LRD for bowel preparation remains a subject of debate and may vary based on individual patient needs and preferences in real-world practice.

Supplementing RCTs with real-world data can enhance the applicability of study results. In this issue of Advances in Digestive Medicine, Yeh et al. conducted a retrospective, single-center (E-Da Dachang Hospital), cross-sectional study to explore the optimal duration of an LRD for bowel preparation before colonoscopy. The authors compared the effectiveness of a 3-day LRD and a 1-day LRD by assessing bowel preparations using the Aronchick score and other quality metrics. The predominant use of sodium picosulfate, magnesium oxide, and citric acid as the oral bowel cleansing agent was observed in the study. The results showed no significant differences between the two groups in terms of adequate bowel preparation, cecal intubation rate, adenoma detection rate, and right-side adenoma detection rate. Notably, the 1-day LRD group had a higher detection rate of advanced adenomas (5.9% vs. 3.4%, P = .002) and sessile serrated lesions (8.9% vs. 6.3%, P = .014). The choice of laxatives and the use of supplemental laxatives did not impact the quality of bowel preparation.¹⁴ These findings align with updated guidelines and provide valuable insights for clinicians.^{9, 11, 14}

Despite the significant advancements in understanding the optimal duration of a 1-day LRD for bowel preparation before colonoscopy, there remain unanswered questions regarding its impact on hard-to-prepare patients. Hard-to-prepare patients may require a longer duration of dietary restriction or additional interventions to overcome their specific challenges. In addition, the impact of a 1-day LRD on individuals with underlying diseases requires further investigation. Patients with conditions such as DM, inflammatory bowel disease, gastrointestinal motility disorders, or malabsorption syndromes may have specific dietary requirements or restrictions that could affect the effectiveness of bowel preparation. Understanding how these underlying diseases interact with the 1-day LRD and whether modifications are needed to optimize bowel cleansing is an important area for future research.¹⁵ To address these unanswered questions, future studies should focus on including diverse patient populations with varying baseline bowel habits and underlying diseases. Large-scale, RCTs conducted across multiple centers are needed to provide robust evidence and establish tailored recommendations for these specific subgroups.

In conclusion, the search for the optimal duration of LRD for bowel preparation continues. The studies conducted thus far, including the E-Da Dachang Hospital study, provide valuable insights into the effectiveness and tolerability of a 1-day LRD. By continuously improving bowel preparation techniques and adherence to screening guidelines, we can enhance the effectiveness of colonoscopy in preventing CRC and improving patient outcomes.

The author declares no conflict of interest.