Dietary fibre
Also called: fibre, fiber, wholegrains.
Last reviewed 2026-09-16. How this works.
Immunotherapy response Grade C
Human evidence exists and does not settle it.
People eating more fibre seemed to respond better to immunotherapy, though nobody has tested it properly yet.
Observational, in melanoma, with a randomised trial registered.
The claim
The claim is that eating more fibre improves how well immunotherapy works, by feeding the gut bacteria that treatment appears to depend on.
What it does
Fibre is not absorbed; it is food for gut bacteria. The mouse work in the same study is what ties the effect to the bacteria rather than to the food: in germ-free mice, which have no gut bacteria, fibre made no difference at all.1
The evidence
The gut microbiome and clinical features were profiled in 438 people with melanoma, of whom 293 had evaluable responses to treatment, most of them receiving checkpoint immunotherapy. Higher fibre intake was associated with better response.1
The germ-free mouse control is the most important part of the study and the part summaries drop. Without gut bacteria, the fibre effect disappeared. That is what turns a dietary correlation into a mechanism.1
This is observational in people. Those who eat more fibre differ from those who eat less in many ways, and the study cannot separate the fibre from the rest.1
The studies this rests on
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Dietary fibre, the gut microbiome and melanoma immunotherapy response (NCT04645680)1
An observational study, measured a clinical outcome, 438 participants.
higher fibre intake associated with better response to immune checkpoint blockade; in germ-free mice fibre made no difference.
What is absent
No completed randomised trial has tested whether increasing fibre changes how well immunotherapy works. The human evidence here is observational and a trial is registered.
Scope: fibre intake and immunotherapy response in people.
Established by trial scope, checked 2026-09-16. Result: the human arm of this study profiled existing intake rather than assigning it.1
What to ask
Is there anything about what I eat that would help this treatment work better?
The dish-to-person gap
Fibre is eaten as food rather than taken as a measured compound, and it acts on the bacteria in the gut rather than by reaching a concentration in the blood.
When to call your team — no warning signs are recorded
If you have changed how you eat because of something you have read, or are thinking about it, the people treating you can only weigh that if they know about it. That is true when nothing has been written down here, and it is most true then.
The register records no warning signs for this entry. Changes to diet during treatment are worth mentioning to the team, particularly after bowel surgery.
Interactions
The register holds no measured interaction between dietary fibre and a cancer treatment class.
Nobody having looked is not the same as nothing being there. That is what this line says and all it says.
The whole interaction list, and how to turn it into a pharmacy review request.
Find a trial instead
A randomised trial is registered on the note behind this entry, which is unusual for a dietary question.
Search ClinicalTrials.gov for recruiting studies of dietary fiber OR fiber melanoma
A trial is the same decision with monitoring, a known preparation and a doctor who knows what else you are taking.
References
Spencer CN, McQuade JL, Gopalakrishnan V, et al, and 86 further authors. Dietary fiber and probiotics influence the gut microbiome and melanoma immunotherapy response. Science 2021;374(6575):1632-1640.
doi:10.1126/science.aaz7015 · NCT04645680
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 7. The author string is abbreviated in the source that was read and has not been expanded.