My gut hurts. Should I eat more fibre or less?

They are talking about the same people and the caveat is that neither is talking about the ones for whom this is dangerous. Bulsiewicz's own claim is addressed to people mid-treatment for a diagnosed condition, often on antibiotics, and he does not name the people who should not ramp fibre at all: anyone with a stricture, active inflammatory bowel disease, or a history of bowel obstruction. That warning is added here; he does not state it.

Baker's claim is addressed to people who may not have been assessed at all, and chronic constipation and IBS are diagnoses of exclusion, so self-managing either by elimination delays finding out what else it might be. Bulsiewicz's own red-flag practice is the missing safety layer under both positions, and it belongs with this disagreement whichever side you take.

The one population Bulsiewicz explicitly hands to the other side is people with Crohn's disease or ulcerative colitis, for whom he says telling them to eat more fibre is not easy and they should start with non-food levers instead. That is closer to Baker's practical position than either would put it.

More than the framing suggests, and the overlap is the useful part. Both accept that reducing fermentable material relieves symptoms in the short term, and Bulsiewicz says so explicitly: the low FODMAP data are clear and people generally improve. Both reject the idea that you should push through pain. The disagreement is entirely about the endpoint. Bulsiewicz treats reduction as a stage with a planned exit, and considers a person cured when they can eat more foods than before. Baker treats reduction as the destination.

So the question a user is actually deciding is not "fibre or no fibre", it is "is feeling better now the goal, or is being able to eat normally later the goal", which is the optimize-for-tonight against optimize-for-age-90 axis wearing a digestive costume.

A randomised trial of gradual fibre reintroduction against sustained elimination in diagnosed IBS, with symptom scores and quality of life at twelve months rather than at six weeks, which neither side has.

Short of that, the two positions make different predictions about the same person over different timescales, so long-run follow-up of people who took each path would separate them. Bulsiewicz's side would also be much stronger if the Nature Communications study he cites on air could be identified; it has not been.