Colonoscopy Prep: Overturning the Clear-Liquid Diet

David A. Johnson, MD


October 19, 2020

This transcript has been edited for clarity.

Hello. I'm Dr David Johnson, professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia.

Do we need to keep doing something simply because that's the way we've done it forever? This question has particular relevance when it comes to recommending a clear-liquid diet before colonoscopy.

We know that colonoscopy is very much predicated on the willingness of the patient to undergo adequate bowel preparation beforehand. If the process of preparation is uncomfortable, that might affect the quality of the colonoscopy. We also know that approximately 50% of patients have reported being unwilling to repeat colonoscopy because of an adverse perception of the clear-liquid diet preparation. Clearly, we can do better.

As we talk about getting more people into colonoscopy screening, particularly in light of COVID-19 and concerns about patients wanting to stay home, doing a procedure with reduced preparation requirements becomes more and more attractive.

A clear-liquid diet is something that we've been traditionally taught to do the day before the colonoscopy. I was part of an earlier US Multi-Society Task Force looking at the issue of colon preparations, which offered recommendations that the low-residue diet should be offered as a potential option for patients. It hasn't received as much traction as I think it should.

Therefore, kudos to the authors of a recent study from China, who looked at low-residue diet vs clear-liquid diet for bowel preparation a day before colonoscopy. They did an extremely good job in providing a statistical analysis drawn from over 4300 patients participating in 20 randomized controlled trials (17 published, three abstracts), which assessed outcomes related to bowel preparation.

They used a meta-analysis conducted according to the best standards and including high-quality studies, as evaluated by the Jadad score system. Then, they performed something very interesting called a trial sequential analysis, which considers the futility of the study over a period of time. Basically, this separate analysis is done to help eliminate type 1 errors (early false-positives) in some of these studies.

The authors found that there was no difference as it relates to the adequacy of the bowel preparation for either a clear-liquid diet or a low-residue diet. The groups had similar rates of polyp and high-risk adenoma detection, as well as cecal intubation. However, there were significantly fewer adverse events in the low-residue diet as it relates to things like nausea, vomiting, hunger, and headache. And significantly more patients in the low-residue diet found it easier to complete the diet (odds ratio, 1.86) and also reported a greater willingness to repeat it (odds ratio, 2.23).

When we look at these data a little more closely with the trial sequential analysis, these other endpoints didn't meet the absolute numbers required to show significance. What we can say is that the low-residue diet equaled the clear-liquid diet as far as the adequacy of the preparation, which is very important to patients. However, these outcomes still require further evaluation before we can offer real scientific support for a low-residue diet over a clear-liquid diet.

We need to look at our colonoscopy preparations, because we can do better by beginning to liberalize them. We cannot yet say this is for every patient, given that the current meta-analysis excluded patients with diabetes, renal dysfunction, and certain other criteria (ie, there were no children involved in this study). So, this may not be a regimen that you'd offer for everybody, but you should start looking to offer it to many of your patients.

Jerry Waye, a good friend and one of the godfathers of colonoscopy recognized for his expertise over decades, told me once that when he offered colonoscopy preparations, he'd tell patients they could have ice cream for dinner the night before. He was a hero in so many patients' eyes. He told me the patients loved it. They never complained about the prep.

In conclusion, consider a low-residue diet and potentially liberalizing the foods, certainly for breakfast and lunch, that can be eaten the day before the colonoscopy. Look closely at this, track it, and see if we can do more to get patients saying, "You know, the prep wasn't bad."

We can also do better by getting these recommendations out to the general population and getting more people into colon cancer screening using the best tool available: colonoscopy. So liberalize, but don't compromise. I think we can do a better job.

I'm Dr David Johnson. Thanks again for listening.

David A. Johnson, MD, a regular contributor to Medscape, is professor of medicine and chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia, and a past president of the American College of Gastroenterology. His primary focus is the clinical practice of gastroenterology. He has published extensively in the internal medicine/gastroenterology literature, with principal research interests in esophageal and colon disease, and more recently in sleep and microbiome effects on gastrointestinal health and disease.

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