Understanding Fibre: Soluble vs. Insoluble and Why It Matters for Your Gut

Protein has dominated the health conversation for years. And while many people weren’t eating enough of it to begin with, the shift toward high-protein diets hasn’t worked for everyone. For some, it’s been unsustainable. For others, it’s come with digestive issues, fatigue, or simply feeling worse.

Now, fibre is stepping into the spotlight, but just to say “eat more fibre” is easier said than done.

Firstly, there’s so many different categories of fibres – soluble fibre, insoluble fibre, fermentable fibres, FODMAPs. A Chihuahua and a Doberman are both dogs, but they are both completely different. Each fibre plays a different role in your gut. And for many, getting fibre wrong can actually make things worse, not better.

If you’ve ever felt bloated, uncomfortable, or worse when trying to “eat healthier,” this is where understanding fibre properly changes everything. So many people think that by eating healthier, they will start to “get better” or feel better. It’s not that simple.

Why Fibre Deserves Your Attention

Fibre is one of the most powerful tools for gut health—but only when it’s used correctly.

I don’t know how many times I’ve heard the “I tried fibre and it didn’t work for me.” Then, finding out they went head strong into psyllium husk or inulin gummies. These fibres are on complete different ends of the spectrum. One ferments very quickly in the gut. The other, very slowly. What fibres you can tolerate depend on your gut.

Fibre does far more than just “keep you regular.” It plays a central role in:

• Feeding beneficial gut bacteria

• Supporting immune function

• Regulating blood sugar

• Producing short-chain fatty acids (SCFAs)

• Reducing inflammation and supporting the gut lining

• Increasing lifespan

• Regulating immunity

• Supporting weight loss

• Supporting Kidney function

• And so much more

Simply adding a scoop of psyllium to your routine won’t necessarily fix underlying gut issues. The type, dose, and timing of fibre all matter.

The Main Players: Soluble vs. Insoluble Fibre

Soluble Fibre: The Fermentable Support System

Soluble fibre dissolves in water to form a gel-like substance in the digestive tract. Many of these types are fermentable, meaning they feed and are broken down by gut bacteria.

When fermented, these fibres produce short-chain fatty acids like butyrate, which:

• Support the integrity of the gut lining

• Reduce inflammation

• Provide fuel for colon cells

Common sources include:

• Oats

• Legumes

• Apples

• Chia seeds

• Pectins and gums

Soluble fibre can also help:

• Slow glucose absorption

• Improve satiety

• Support cholesterol regulation

For many people, this is the most therapeutically useful category of fibre. But it still needs to be introduced appropriately.

Insoluble Fibre: The Motility Driver

Insoluble fibre does not dissolve in water. Instead, it adds bulk to stool and helps move food through the digestive tract.

Think of it as a mechanical support system for bowel regularity.

Common sources include:

• Whole grains

• Nuts and seeds

• Vegetable skins

• Bran

While insoluble fibre plays less of a direct role in fermentation (though it can still ferment) compared to soluble fibre, it still contributes to gut health by:

• Supporting bowel motility

• Preventing constipation

• Influencing the gut environment indirectly

However, in sensitive individuals, too much insoluble fibre, especially too quickly, can aggravate symptoms.

Semi-Soluble and Soothing Fibres

Some fibres sit between these two categories or have unique functional properties.

Mucilaginous fibres, such as:

• Slippery elm

• Marshmallow root

Form a soothing gel that can help:

• Calm irritation in the digestive tract

• Support the gut lining

• Improve tolerance in inflamed or sensitive guts

These fibres are particularly useful in clinical settings where the gut is reactive or damaged.

The Nuanced Reality: When Fibre Feels Complicated

Most general advice says: eat more fibre.

But clinically, it’s not that simple.

Many people feel worse when they increase fibre intake, and this isn’t a failure. It’s a sign that the gut requires a more personalised approach.

FODMAPs and Fibre Sensitivity

FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) are fermentable carbohydrates, some of which overlap with certain types of fibre.

In people with IBS, these compounds can ferment rapidly, leading to:

• Gas

• Bloating

• Abdominal discomfort

High-FODMAP foods include:

• Onion and garlic

• Certain legumes

• Wheat-based products

• Some fruits

This doesn’t mean fibre is the problem—it means the type and fermentability of fibre matters.

Lower-FODMAP fibre sources such as:

• Carrots

• Zucchini

• Rice

• Certain fruits

Are often better tolerated while the gut is being supported. But the nuance here is that FODMAP foods should not be avoided long term. Reacting to FODMAPs is a sign that something is imbalanced in the gut – restoring balance can overcome these reactivities and allow you to eat a more diverse, healthy diet again.

Why Fodmap Sensitivity Happens

What can be causing your issues with FODMAPs:

• SIBO – Small Intestinal Bacterial Overgrowth – bacteria in the wrong place

• Dysbiosis – Some microbes may be completely over-dominating others

• Visceral hypersensitivity – The nerves in the gut overreact

• Impaired motility – The gut doesn’t move things along allowing improper fermentation

• Enzyme deficiencies – Lactose intolerance can push things down too quickly

• Intestinal permeability – Gut contents leaking out of the gut causing inflammation

• Genetics – Some genes can affect microbiome levels

• Liver/gallbladder issues – Poor bile flow = slow gut movement

• Poor diet – Low FODMAP diets increase FODMAP sensitivity

• Infection – This one is self explanatory

• Medication – Many medications indirectly affect gut functions

Most of these issues can be addressed clinically. If you think going FODMAP free for life is your only option, think again!

IBD: A Different Consideration

In inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, fibre tolerance changes depending on disease activity.

During flare-ups:

• Insoluble fibre can be irritating

• High-residue foods may worsen symptoms

More suitable options often include:

• Cooked and peeled vegetables

• Softer, soluble fibre sources

• Lower-residue foods

Again, this highlights a key principle:

Beyond the Gut: The Bigger Picture

Fibre doesn’t work in isolation.

When you increase fibre through whole foods, you’re also increasing intake of:

• Polyphenols

• Vitamins and minerals

• Antioxidants

Polyphenols, in particular, work synergistically with fibre to:

• Support beneficial bacteria

• Reduce inflammation

• Improve metabolic health

This is why whole food diversity is so important. It’s not just about hitting a fibre target—it’s about creating a healthy ecosystem within the gut.

We understand a great deal about vitamins but there are thousands of additional bioactive compounds inside whole foods, beyond just vitamins, that play essential roles in supporting overall health.

Finding Your Fibre Sweet Spot

Minimal daily fibre recommendations are 30g for men and 25g for women where most people are consuming 15-20g or less

But fibre is not one-size-fits-all.

The goal isn’t to eat as much fibre as possible, it’s to find the types and amounts that your gut can tolerate and benefit from.

A practical approach:

• Introduce fibre gradually

• Pay attention to symptoms (bloating, gas, stool changes)

• Adjust types of fibre, the quantity and the timing

• Focus on diversity over volume

If symptoms worsen, it’s often a sign to step back and revisit later.

When to Get Personalised Support

If you’ve ever:

• Felt worse on high-fibre diets

• Struggled with bloating or irregular bowels

• Tried to “eat healthy” but didn’t feel better

Then your gut likely needs a more tailored approach.

In clinic, I use:

• Dietary analysis

• Symptom tracking

• Functional testing (including microbiome analysis)

To determine exactly:

• Which fibres your gut tolerates

• Which ones are causing symptoms

• And how to rebuild tolerance over time

Ready to Fix Your Gut Properly?

If you’re tired of guessing what works for your body, you don’t have to figure it out alone.

Book a naturopathic, functional medicine consultation and we’ll build a personalised plan that identifies the right types of fibre for your gut- so you can feel better, not worse.