More fibre, more bloating? New research on why fibre isn’t one-size-fits-all

Fibre is the golden child of gut health and for good reason. But better gut health isn’t about winning a fibre-eating contest.

In clinic, I regularly see people who’ve loaded up on “gut-healthy” foods, only to end up more bloated than when they started. More beans, more bloat, more “what on earth is happening?”

Often the issue isn’t that they’re eating the wrong foods. It’s the type of fibre, the serving size or how quickly they’ve ramped up.

A fascinating new study, published on 2 October 2026 in Nature Microbiology, adds another layer. How a fibre behaves depends partly on which bacteria are already living in your gut.

Here’s the research behind why fibre isn’t one-size-fits-all.

What did the researchers discover?

The study, Synergy between Enterobacteriaceae and diet mediates competition between dominant Bacteroidales in the human gut, looked at how dietary carbohydrates influence competition between two major groups of gut bacteria. The first group, Bacteroidaceae, is common in industrialised populations. The second, Prevotellaceae, is more common in traditional, plant-rich populations.

The team built a lab-grown community of 21 human gut bacteria and tested 94 dietary components against it, including 79 complex carbohydrates.

More than half of them gave a boost to Segatella copri, a key member of the Prevotellaceae group. One plant carbohydrate, arabinan, was studied in detail.

Here’s the plot twist. When S. copri went head to head with Bacteroidaceae on its own, it lost, even with arabinan on the menu. It only came out on top when E. coli was added to the mix.

Yes, E. coli. Not the wingman I’d have picked either. (And no, this isn’t a reason to go looking for more of it.)

Other members of the same bacterial family, the Enterobacteriaceae, had a similar effect. Even more intriguing, the sugars released as the fibre was broken down seemed to act more like chemical signals than food. A bacterial group chat, if you like.

The researchers then tested this in lab-cultured communities grown from human stool and mouse gut samples. They also saw a consistent pattern in existing microbiome data from healthy adults around the world.

The big principle is that the effect of a fibre depends on who’s already living in your gut. Your microbiome works as an interconnected ecosystem, not a collection of isolated bacteria.

What does this mean for gut health?

Different fibres have different physical and chemical properties. Some are fermented rapidly by gut bacteria, some slowly, and some resist fermentation altogether.

Fermentation produces beneficial compounds, including short-chain fatty acids. It also produces gas.

For people with sensitive digestion, particularly those with IBS, constipation or bloating, the type and amount of fibre can make a real difference to symptoms.

That said, symptoms aren’t driven by the microbiome alone. Bowel transit, gut sensitivity, food composition and other physiological factors all play a part.

Why I favour a personalised, food-first approach

In practice, it usually comes down to choosing the right fibres and preparing them well. For example:

• Psyllium is a soluble, gel-forming fibre with good clinical evidence for improving IBS symptoms.

• Partially hydrolysed guar gum (PHGG) is slowly fermented, tends to be well tolerated, and has promising evidence for bowel function.

• Inulin and fructooligosaccharides (FOS) are rapidly fermented and may aggravate gas-related symptoms in sensitive individuals.

• Whole foods such as oats, legumes, vegetables, nuts and seeds offer a mix of fibre types, plus plenty of other valuable nutrients.

How you prepare them matters too. Traditional methods like soaking, sprouting, rinsing and slow cooking can make legumes and grains easier to digest for many people. Even rinsing canned beans and giving extra cooking time helps, so the tin in my photo isn’t a cop-out. I’ve put my go-to methods into a Prep Like a Pro fridge guide, linked at the end.

The goal isn’t to eliminate foods that cause discomfort. It’s to understand individual tolerance, introduce fibres gradually and work towards a more varied diet wherever possible.

My takeaway

Variety matters, and so does pace. Increase your fibre at a speed your digestive system can keep up with, choose fibres that suit your gut right now and remember your microbiome starts responding to what you eat within a day or two.

This is where my chef hat and my clinician hat get to share the kitchen. Understanding what happens inside the gut is valuable. Knowing how to turn that into everyday meals is where it becomes useful.

Want to go further?

• 4R Gut Reset & Repair Program (launching soon): a step-by-step, food-first program to help you identify your triggers, settle symptoms and reintroduce foods, fibre included, at a pace your gut can handle. Join the waitlist

• Prep Like a Pro: my fridge-friendly guide to soaking, sprouting and cooking grains, beans, legumes, nuts and seeds. Grab yours here

Over to you: have you ever increased your fibre and ended up more bloated, which fibre or food did you react to the most? I’d love to hear your experience in the comments.

Love Your Guts 💚 Leilani

Research Tawk C, El Mouali Y, et al. (2026). Synergy between Enterobacteriaceae and diet mediates competition between dominant Bacteroidales in the human gut. Nature Microbiology. doi:10.1038/s41564-026-02500-6

David LA, et al. (2014). Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–563.

Additional clinical evidence: American College of Gastroenterology clinical guideline for the management of IBS (2021) and Monash University research on dietary fibre and fermentability