What It Actually Does, How Much You Need & Why Your Microbiome Cares
Most people know fibre is “good for you.”
Usually the explanation stops somewhere around:
“It helps you poop.”
Which is true.
But it’s a bit like describing sleep as something that stops you from feeling tired.
Technically correct. Slightly missing the bigger picture.
When I first started properly researching gut health, fibre was probably the nutrient I realised I had underestimated the most.
Because fibre isn't one single thing.
Different fibres behave differently in the gut. Some hold water. Some affect stool consistency. Some are fermented extensively by gut bacteria. Some are only partially fermented. And that fermentation can produce metabolites such as short-chain fatty acids that interact with the gut environment and the rest of the body.
So this article isn't going to tell you that fibre is magic.
It isn't.
But I do think it's one of the most boring-sounding parts of nutrition with one of the most interesting bodies of research behind it.
Let's get into it.
First: How much fibre do we actually need?
There isn't one magical number where 24.9 grams is bad and 25 grams suddenly unlocks perfect health.
But we do have some very solid reference points.
The World Health Organization recommends that adults consume at least 25 g of naturally occurring dietary fibre per day.
EFSA considers 25 g per day adequate for normal bowel function in adults and notes that higher intakes are associated with additional health benefits.
And here in the Nordics, the Nordic Nutrition Recommendations 2023 recommend at least 3 g/MJ, corresponding to approximately:
25 g/day for women
35 g/day for men
Nordic Nutrition Recommendations 2023
And this isn't based on fibre influencers arguing with each other on Instagram.
One of the biggest analyses in this area was published in The Lancet in 2019.
Researchers brought together data from 185 prospective studies and 58 clinical trials, representing almost 135 million person-years of observational data.
The greatest risk reductions across several major health outcomes were associated with fibre intakes around 25–29 g per day, while the dose-response analyses suggested that higher intakes may provide additional benefits for some outcomes.
So rather than pretending there is a scientifically established “perfect” intake of exactly 37 grams, I think the more useful takeaway is:
Get at least 25–35 g per day depending on your needs, and don't be scared of getting more from a varied, fibre-rich diet if your gut tolerates it.
Research: Reynolds et al., 2019 — Carbohydrate quality and human health: a series of systematic reviews and meta-analyses.
The problem: a lot of us aren't getting there
This isn't really a theoretical problem.
Across European dietary surveys, average adult fibre intake has generally been reported below recommendations.
EFSA reported averages ranging from approximately 15.7 to 29.5 g/day across European adult populations, with almost all surveyed populations falling below its adequate intake.
A large review of European intake data found approximately:
Men: 18–24 g/day
Women: 16–20 g/day
And because Lumière started in Denmark, this one is particularly interesting to me:
Nordic Nutrition Recommendations 2023 concluded that fibre intakes remain below the recommended minimum across the Nordic and Baltic countries.
So when people say:
“Surely everyone gets enough fibre just by eating normally?”
Well...
Apparently not.
Research: EFSA — European dietary fibre intake.
Research: Carlsen & Pajari, 2023 — dietary fibre review for Nordic Nutrition Recommendations 2023.
But fibre isn't just about hitting a number
This is where the conversation gets more interesting.
Imagine two people both eat 30 g of fibre.
One gets most of it from the same cereal product every day.
The other gets fibre from whole grains, oats, legumes, berries, vegetables, fruit, nuts, seeds and resistant starch.
Both technically ate:
30 g fibre.
But biologically, those diets aren't necessarily identical.
Because fibre isn't one molecule.
Dietary fibre is an umbrella term covering compounds with different structures, physical properties and degrees of fermentation.
And our gut microbes don't treat every fibre identically either.
That's why I think there are really two useful questions:
1. Are you eating enough fibre?
And then:
2. Where is that fibre actually coming from?
What happens to fibre after you eat it?
Some fibres aren't fully digested in the small intestine.
They continue into the large intestine, where some can be fermented by microorganisms living there.
And this is where fibre gets much more interesting than “roughage.”
During fermentation, gut microbes can produce metabolites including the major short-chain fatty acids (SCFAs):
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acetate
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propionate
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butyrate
These aren't just waste products.
SCFAs participate in communication between our gut microbes and our own cells and have been extensively studied in relation to intestinal physiology, metabolism and immune signalling.
But there's another important detail:
Different fibres produce different responses.
The extent and location of fermentation can differ.
The microbes capable of utilising them can differ.
And your response can differ from mine because our existing microbiomes aren't identical.
This is why I'm personally much more interested in fibre diversity than finding one supposedly perfect fibre.
What does the human research actually show?
This is one of my favourite studies to bring up because it also stops us from overhyping the microbiome.
A 2018 systematic review and meta-analysis analysed 64 controlled studies involving 2,099 healthy adults.
Compared with placebo or lower-fibre controls, fibre interventions increased:
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Bifidobacterium
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Lactobacillus
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faecal butyrate concentrations
That's pretty interesting.
But the researchers didn't find a significant overall increase in alpha diversity.
I actually like that result.
Because “MORE FIBRE = MORE MICROBIOME DIVERSITY” sounds amazing on a graphic.
Reality is more complicated.
Individual fibres can shift particular bacteria and microbial activity without magically making every measure of microbiome diversity increase.
That's why we should talk about microbiome composition and function, not just chase one diversity score.
Research: So et al., 2018 — Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis.
Not all fibre does the same thing
This is probably the most important part of the entire guide.
Rather than dividing fibre into “good” and “bad”, I think it's more useful to understand what different fibres actually do.
1. Fermentable fibres
These are the fibres your gut microbes can use as substrates to varying degrees.
Examples include:
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inulin-type fructans
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resistant starch
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PHGG
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pectins
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beta-glucans
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some components of acacia fibre
Their fermentation can influence microbial populations and produce metabolites including SCFAs.
But even within this category, there are big differences.
Inulin is not resistant starch.
Resistant starch is not PHGG.
And PHGG is not pectin.
Different structure.
Different fermentation.
Different microbial response.
Which is precisely why saying “fibre is fibre” doesn't make much sense.
2. Gel-forming and stool-normalising fibres
Then you have fibres such as psyllium.
Psyllium is interesting because its benefits aren't dependent on it being some insane microbiome superfood.
Its physical properties matter.
It interacts with water and can help normalise stool consistency.
A 2022 systematic review and meta-analysis of fibre supplementation in chronic constipation found that fibre supplementation improved several constipation outcomes, with psyllium among the fibres showing significant effects.
Sometimes physiology doesn't need a sexy explanation.
Sometimes helping your poop be normal is already a pretty useful feature.
Research: van der Schoot et al., 2022 — systematic review and meta-analysis of fibre supplementation in chronic constipation.
3. Fibres that come packaged with other plant compounds
Real food gets even more complicated.
An apple isn't “pectin.”
Oats aren't “beta-glucan.”
Baobab isn't simply “X grams of fibre.”
Plant foods contain mixtures of fibres alongside compounds such as polyphenols, vitamins, minerals and other phytochemicals.
That's one of the reasons I don't like reducing food to individual ingredients.
And it's also why:
Food comes first.
Always.
What about cereal fibre?
This is another place where I want to correct something from the usual internet fibre conversation.
You sometimes hear:
“Grain fibre just adds bulk. It doesn't really feed the microbiome.”
That's too simplistic.
Bread and cereal products are actually major sources of dietary fibre in European populations, and intact cereal fibres and components such as arabinoxylans can affect the gut microbiota.
A systematic review of human intervention studies examining intact cereal fibres found microbiota changes across a large proportion of the included interventions.
So no:
Your oats and whole-grain bread are not useless because they aren't chicory root.
Quite the opposite.
The goal should be diversity, not creating another unnecessary food war.
Research: Jefferson & Adolphus, 2019 — systematic review of intact cereal grain fibres and the gut microbiota.
Where should your fibre actually come from?
The boring answer is also the correct one:
Lots of different plants.
WHO recommends carbohydrate sources come primarily from:
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whole grains
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vegetables
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fruits
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pulses
NNR additionally highlights foods including:
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berries
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nuts
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seeds
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potatoes
And if we're specifically interested in different fermentable substrates, I really like foods such as:
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oats
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barley
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beans
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lentils
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chickpeas
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onions
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garlic
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leeks
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asparagus
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apples
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berries
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slightly green bananas
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cooked and cooled potatoes
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nuts
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seeds
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whole grains
You don't need all of them every day.
Please don't turn breakfast into a 37-ingredient microbiome ceremony.
But over a week?
Variety is a very good idea.
Can you get enough fibre from food alone?
Yes. Absolutely.
I want to make this extremely clear because I sell a fibre product.
You do not need Gut Reset to consume enough fibre.
You can build an incredibly fibre-rich diet from whole foods.
And if someone selling you a fibre supplement tells you that getting fibre from food “doesn't work”, I would probably stop listening to them.
Whole grains, legumes, vegetables, fruit, berries, nuts and seeds should form the foundation.
The problem is not that food can't do it.
The problem is that many people simply don't consistently eat enough of those foods.
That's a very different argument.
So why would anyone supplement fibre?
Convenience.
Consistency.
And, depending on the product, access to particular fibre types in a controlled amount.
That's it.
Not because fibre powder has discovered a secret biological pathway unavailable to broccoli.
I personally eat fibre-rich foods every day.
And I still like having a repeatable daily baseline that doesn't depend on whether today was a perfectly planned nutrition day or an airport-and-three-meetings kind of day.
That's how I think supplementation should work:
Food establishes the foundation.
Supplementation can make the foundation easier to maintain.
Not replacement.
Support.
Do we have an official target for “prebiotic fibre”?
This is important.
No universally accepted recommendation says every adult needs exactly 10 or 15 grams of “prebiotic fibre” per day.
And I don't think we should invent one because it makes a nice infographic.
“Dietary fibre” and “prebiotic” aren't interchangeable terms either.
The scientific consensus definition of a prebiotic is a substrate that is selectively utilised by host microorganisms and confers a health benefit.
So while many fermentable fibres interact with the microbiome, we shouldn't automatically label every fibre a clinically proven prebiotic.
This is one of those distinctions that sounds annoyingly nerdy.
But it's actually important.
The modern fibre problem is therefore really two problems
Problem 1: Quantity
A lot of people simply don't reach recommended total fibre intakes.
That's the obvious one.
Problem 2: Variety
Even if your total number looks decent, it's worth asking whether your fibre comes from a varied range of foods and fibre structures.
This doesn't mean everyone has a diagnosed “microbiome fuel deficiency.”
That's not a recognised nutritional diagnosis.
But I think microbiome fuel gap is a useful way of describing the practical problem:
Many of us eat less fibre than recommended, and our diets often don't contain the variety of fermentable plant substrates they could.
That's a much more accurate version of the idea.
Fibre and blood sugar
Fibre can also affect how we metabolise a meal.
But again:
The type matters.
Certain viscous soluble fibres can slow nutrient absorption and influence post-meal glucose responses.
Whole, fibre-rich carbohydrate foods also tend to behave differently from highly refined carbohydrate foods.
And across the bigger picture, higher-quality carbohydrate diets rich in fibre are associated with better cardiometabolic outcomes.
The 2019 Lancet analysis found that higher fibre intake was associated with lower body weight, systolic blood pressure and total cholesterol in clinical trials, alongside lower incidence of several chronic diseases in prospective research.
So “fibre is good for blood sugar” isn't completely wrong.
It's just less precise than saying:
Different fibres and fibre-rich foods can influence glycaemic responses through different mechanisms.
Research: Reynolds et al., 2019.
Fibre, inflammation and the gut barrier
This is probably where wellness marketing gets most carried away.
You've likely seen the chain:
Fibre → butyrate → fixes leaky gut → removes inflammation → perfect skin.
Biology is not a Domino's delivery tracker.
SCFAs, particularly butyrate, are deeply involved in intestinal physiology and interact with intestinal epithelial cells and immune pathways.
Dietary fibre can influence their production through microbial fermentation.
That's biologically important.
But we should be careful about translating mechanisms directly into guaranteed outcomes in individual humans.
A stronger gut environment and appropriate fibre intake are part of supporting normal gastrointestinal and metabolic health.
They are not a promise that every inflammatory problem in your body disappears.
Okay, but what about your skin?
This is Lumière, so obviously we're going to talk about skin.
There is a growing field of research around the gut–skin axis.
The gut and skin can communicate indirectly through immune, metabolic and neuroendocrine pathways, and researchers are investigating relationships between the gut microbiome and conditions including acne.
But I want to make the distinction very clear:
Eating more fibre is not an acne treatment.
And there isn't a clinical equation that says:
10 g more fibre = 37% fewer breakouts.
I wish skin worked like that.
It would have saved me a lot of time.
What makes fibre interesting in this context is more fundamental.
Dietary fibre can influence the gut microbiome and microbial metabolites.
The microbiome interacts with immune and metabolic systems.
And those systems are among the many biological pathways that can also influence skin.
So I view fibre as part of the foundation.
Not the acne cure.
Research: Sánchez-Pellicer et al., 2022 — Acne, Microbiome, and Probiotics: The Gut-Skin Axis.
Research: De Pessemier et al., 2021 — Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions.
Why I care so much about fibre diversity
Let's come back to the idea that started all of this.
Different fibres have different structures.
Different microbes possess different enzymes.
And different people can respond differently to the same fibre.
That makes the gut microbiome an ecosystem rather than a petrol tank where you simply pour in “10 grams of fibre fuel.”
So I wouldn't say:
One fibre = bad. Multi-fibre = automatically superior.
We don't have evidence to make that blanket claim.
But I do think there is a strong biological rationale for getting fibre from multiple sources, and that's also consistent with dietary recommendations encouraging a varied plant-rich diet.
That's how I eat.
And it's how we approached Gut Reset.
The Lumière perspective
Gut Reset was never meant to replace vegetables, fruit, legumes, oats or whole grains.
Quite the opposite.
I wanted to solve a much more boring, and much more real, problem:
Consistency.
Gut Reset combines seven different fibre sources with different properties in one daily serving.
Some are highly fermentable.
Some ferment differently.
Psyllium brings different physical properties.
And then we combine the fibre blend with Bacillus coagulans and a smaller botanical comfort layer.
Not because seven is a magical number.
And not because your microbiome will collapse if you miss your scoop on Tuesday.
We simply wanted to build a diverse daily fibre base that was ridiculously easy to use consistently.
Then you keep eating real food on top of it.
That's the idea.
So what should you actually aim for?
If you've made it this far, I don't want you leaving with a spreadsheet and anxiety about whether you've eaten 4.7 or 5.2 grams of resistant starch today.
Keep it simple.
1. Get enough total fibre
For most adults, think at least 25–35 g/day, depending on sex, energy intake and the dietary guideline you're following.
2. Get it from different foods
Whole grains.
Vegetables.
Fruit and berries.
Legumes.
Nuts and seeds.
Not one “superfood.”
3. Include fermentable fibres
Oats, barley, legumes, onions, garlic, apples, resistant starch-containing foods and other fibre-rich plants can provide different substrates for the microbiome.
4. Increase gradually
If you're currently eating 12 g of fibre, tomorrow probably isn't the day to eat 45 g and half a bag of Jerusalem artichokes.
Your colleagues will thank me.
Increase gradually and drink enough fluid.
5. Use supplementation for what supplementation is good at
Making something useful easier to do consistently.
Not replacing a good diet.
The one idea I want you to remember
For years, we talked about fibre almost entirely in terms of digestion.
Today, we understand that the story is much bigger.
Fibre-rich diets are associated with better long-term health outcomes.
Certain fibres influence stool function.
Certain fibres are fermented by the microbiome.
That fermentation can change bacterial populations and microbial metabolites.
And different fibres can behave very differently inside us.
So the better question isn't just:
“Did I eat enough fibre today?”
It's:
“Am I consistently eating enough fibre, from enough different sources, to support both me and the ecosystem living inside me?”
That's the way I think about fibre now.
And it's ultimately the thinking that led me to build Gut Reset in the first place.
Not because food isn't enough.
But because doing the right thing consistently is usually the hardest part.
The research behind this guide
If you're like me and would rather actually open the studies than just trust a wellness blog telling you fibre is amazing, start here:
Recommendations & population intake
World Health Organization (2023). Carbohydrate intake for adults and children.
EFSA. Dietary Reference Values for dietary fibre — 25 g/day considered adequate for normal bowel function in adults, with evidence of benefits associated with higher intake.
Nordic Nutrition Recommendations 2023. At least 3 g/MJ dietary fibre, corresponding to approximately 25 g/day for women and 35 g/day for men at reference energy intakes.
Carlsen & Pajari (2023). Dietary fiber – a scoping review for Nordic Nutrition Recommendations 2023.
Fibre & long-term health
Reynolds et al. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet.
Fibre & the gut microbiome
So et al. (2018). Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis.
64 studies and 2,099 participants; fibre interventions increased Bifidobacterium, Lactobacillus and faecal butyrate, without a significant overall increase in alpha diversity.
Jefferson & Adolphus (2019). The Effects of Intact Cereal Grain Fibers, Including Wheat Bran on the Gut Microbiota Composition of Healthy Adults: A Systematic Review.
Psyllium & bowel function
van der Schoot et al. (2022). Systematic review and meta-analysis of fibre supplementation in chronic constipation.
Gut–skin axis
Sánchez-Pellicer et al. (2022). Acne, Microbiome, and Probiotics: The Gut-Skin Axis.
De Pessemier et al. (2021). Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions.
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