The Dietary Fiber Lie We all Believed (until now)

Written by Annette Bosworth, MD on December 21, 2025. Posted in Current News

Dr. Annette Bosworth argues that the common medical advice to eat more fiber for gut health is misleading and potentially harmful for people with chronic inflammation, insulin resistance, or gut disorders.

“I used to believe that fibre would make people healthier, but I was wrong. Healthy poop does not look big and bulky and does not happen many times a day, ” says medical doctor, Annette Bosworth, who has over one million subscribers on her Youtube Channel, Dr. Boz [Annette Bosworth, MD]

1. Traditional fiber advice may be wrong for sick patients

Dr Bosworth admits she previously told patients that healthy digestion required high fiber and daily, bulky bowel movements.
Based on her clinical experience, she now believes this advice worsened symptoms such as bloating, constipation, inflammation, brain fog, and joint pain in metabolically unhealthy patients.
Dr Bosworth distinguishes between healthy individuals (who may benefit from fiber on a standard Western diet) and chronically ill patients, whom she claims often worsen with added fiber.

2. Fiber is not an essential nutrient

Dr Bosworthpoints out that there is no such thing as “essential fiber”:
- Unlike essential amino acids, fatty acids, or vitamins, fiber is not required for survival.
- Dr Bosworth claims humans can live physiologically well without consuming any fiber.

3. Fiber may irritate an inflamed gut

Dr Bosworth describes fiber as indigestible material that physically passes through the gut.
She compares fiber to a scrub brush that can damage the gut’s mucin (protective slime) layer.
In healthy people, she says this layer regenerates quickly.
In people with leaky gut or inflammation, Dr Bosworthargues fiber can worsen damage rather than promote healing.

4. Microbiome diversity doesn’t require fiber

She challenges the idea that fiber is necessary for a healthy microbiome.
According to Dr Bosworth scientists do not agree on which gut bacteria are “good” or “bad.”
She argues the human body can adapt to many dietary patterns, including low-carb, low-fiber, or ketogenic diets.

5. Clinical example: Jane and the zero-fiber diet

Dr Bosworth presents a patient, “Jane,” who had long-standing insulin resistance and inflammation.
Jane followed a strict elimination diet of sardines and MCT oil (essentially zero fiber).
Initial symptoms (diarrhea) occurred during microbiome adaptation.
Over time, Jane’s inflammation improved and bowel movements became infrequent but comfortable and small, which Bosworth describes as healthy and efficient, not constipation.

6. Rethinking constipation and “healthy poop”

Dr Bosworth argues that:
- Constipation is defined by symptoms and discomfort, not frequency.
- Less frequent, smaller stools can indicate high nutrient absorption and low waste.
- Large, bulky stools are not necessarily healthy.

7. Fiber is not required to feed the colon

A common argument for fiber is that gut bacteria ferment it into butyrate, which supports colon health and appetite regulation.
Bosworth claims ketosis provides an alternative:
- The liver produces beta-hydroxybutyrate (BHB) during ketosis.
- BHB is structurally similar to butyrate and can nourish the gut lining via the bloodstream, without fiber fermentation or gas.

8. Dr Bosworth’s conclusion

Fiber may help mitigate damage from processed, high-carb diets in healthy people.
However, she believes fiber harms people with inflamed or metabolically damaged guts.
Dr Bosworth promotes low-fiber, ketogenic, animal-based diets as a better approach for healing in such patients.
She reframes digestion as efficiency, not bulk.

The above reflects Dr. Bosworth’s clinical interpretation and dietary philosophy, which differs from mainstream nutritional guidelines. Her claims are controversial and not universally accepted in gastroenterology or nutrition science. This content is strictly the opinion of Annette Bosworth, MD.

[PSI Editor note: Just my own anecdotal experience, but since switching to a high protein/low carb/low fiber diet six months ago, I feel much healthier – but I accept we are all different]

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