Shawn BakerMD · orthopedic surgeon and strength athlete
None. Remove plant fiber entirely and see if the symptoms go.
What it rests onReported symptom resolution in people who eliminate plants, framed as an elimination diet: if fiber is the irritant, subtracting it is the test.
Source: carnivore.diet ↗
Michael GregerMD · founder, NutritionFacts.org
More. Constipation is a fiber-deficiency disease and the first-line answer is to raise intake.
What it rests onPopulation data on bowel-movement frequency by diet pattern, and guideline first-line treatment for constipation.
Source: nutritionfacts.org ↗
Gil CarvalhoMD, PhD · nutrition and aging researcher, creator of Nutrition Made Simple!
More, and if fiber hurts, that is a specific intolerance to identify rather than a verdict on fiber.
What it rests onLarge analyses find lower risk of heart disease, stroke, type 2 diabetes, colorectal cancer and death in high-fiber consumers after accounting for smoking and exercise, and randomised trials of added fiber report lower weight, blood pressure and cholesterol. He carries the exception in the same section: conditions such as IBS cause intolerance to specific foods, removing those often helps, and he treats the intolerance itself as potentially reversible.
Source: gilcarvalhomdphd.substack.com ↗
Three answers, and only one of them is aimed at the person who asks this in a bad week. Baker is talking about people with diagnosed IBS or chronic constipation who have already failed conventional advice, which is a small and self-selected group. Greger and Carvalho are both talking about the general population, most of whom eat well below any recommended intake, and Carvalho's own exception, a specific intolerance to identify rather than a verdict on fiber, is aimed at exactly Baker's group.
So the thing to work out first is whether your gut is a mess in the way Baker means, with a diagnosis behind it, or simply unused to fiber.
All three accept that a subgroup of people genuinely feel worse on fiber and that this is not imaginary. All three hold that fluid intake matters, that ultra-processed food is the wrong answer, and that your own bowel response is the measure that counts. Carvalho concedes the technical point Baker leads with, that fiber is not an essential nutrient, and argues it is irrelevant to whether you should eat it.
A randomised trial of fiber elimination against fiber escalation in diagnosed IBS, with symptom and quality-of-life endpoints. None of the three has one. Carvalho's reversibility claim adds a second testable question, and it is the one that would move him: whether tolerance recovers on graded reintroduction.
You do, and your call is dated, kept, and yours to change. Follow the people you already trust and what they publish turns into a short daily practice.
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