How good is the evidence

It would be easy to write this book as though the ground under it were solid. It is not, and you are better served knowing that.

What is well evidenced

One thing, clearly. Low-residue eating before a colonoscopy has several systematic reviews and meta-analyses behind it. They find it gives a view as good as clear fluids alone, with less hunger, less nausea and more willingness to go through the preparation again, and there is reasonable evidence that a single day of restriction may do as much as three. That is a procedural question rather than a disease-management one, but it is the firmest finding in this whole area. See before a colonoscopy or surgery.

What is thin

Almost everything else. The research behind this book found no Cochrane review of the low-fibre diet for bowel rest after colorectal surgery, for stricture management or for malignant obstruction. A 2025 scoping review of dietary modification in malignant bowel obstruction found seven eligible studies, mostly conference abstracts and feasibility work, and concluded that there is a lack of evidence to support the practice and that proper trials are needed. A four-step obstruction diet developed at Royal Surrey showed promising results in a small feasibility study, not a definitive trial. Dietary management of LARS is described as first-line in the material handed to people living with it, and rests mainly on small studies and trial and error.

A widely cited 2016 review went further and concluded there was insufficient evidence to justify the clinical use of a low-residue diet as traditionally defined. That finding is why the American Academy of Nutrition and Dietetics removed the term "low residue diet" from its manual altogether: there is no accepted definition of residue, no way to measure it and no agreed cut-offs. UK practice is mid-transition, and the East Lancashire leaflet this book follows brackets both terms together in its own title.

What that means for you

Not that the advice is wrong. The mechanical argument is sound, the clinical consensus is genuine and consistent across every trust compared, and a piece of sweetcorn does not digest whichever way the trials fall. It means that clinical practice here runs ahead of the trial evidence, that the disagreements between trusts are honest ones rather than errors, and that nobody should be on this diet indefinitely without review.

Worth knowing in the other direction: among people who have finished treatment, higher fibre intake is associated with lower mortality. Low fibre is a short-term tool for a specific problem. It was never a long-term recommendation.

Every source this book leans on is listed at sources.