If you’ve ever had “butterflies” before a big event or lost your appetite when stressed, you’ve experienced the gut-brain connection in action. Emerging research shows that the trillions of bacteria living in your gut – friends with benefits (collectively known as the gut microbiome) are a key regulator of gut-brain function and have a powerful influence on mood, stress response, and even hormone balance.

And one of the easiest — yet most overlooked — ways to nurture this connection is through dietary fibre.

In this article we’ll explore how fibre may literally help you feel happier.

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What Is the Gut-Brain Axis?

The gut-brain axis is a two-way communication system between your digestive tract and your brain. It connects the central nervous system (your brain and spinal cord) with the enteric nervous system (the “second brain” in your gut) — allowing your gut and brain to constantly “talk” to each other through nerves, hormones, and immune messengers.¹

These two pathways communicate through various systems including:

The vagus nerve, the most direct pathway linking the gut to the brain sending messages from gut to brain in milliseconds

Immune molecules and metabolites produced by gut microbiome, our immune system is one of the most direct signalling pathways along the microbiota-gut-brain axis. The highest concentration of immune cells is located within the GI tract, these cells are in constant communication with the gut microbiota to identify potentially harmful pathogens. ²

Hormones and neurotransmitters, like serotonin and dopamine

At the heart of this network lies the HPA axis, short for the Hypothalamic–Pituitary–Adrenal axis — your body’s main stress response system.

How the HPA axis works: When you experience stress, the HPA axis triggers the release of cortisol, the hormone that prepares your body to “fight or flee.” In small doses, this response is helpful. But chronic activation — the kind that happens with ongoing stress or poor gut health — can disrupt digestion, sleep, and mood.

Here’s how your gut plays a role in regulating this system:

• Stress and the gut: Chronic stress can disturb your gut microbiome, reducing levels of beneficial bacteria and increasing intestinal permeability (sometimes called “leaky gut”).
• Gut to brain: When the gut is inflamed or imbalanced, it sends distress signals to the brain through the vagus nerve and immune molecules.
• Brain to gut: This can overstimulate the HPA axis, keeping cortisol levels high — a cycle that contributes to anxiety, fatigue, and low mood.
• Restoring balance: A diverse, fibre-fed gut microbiome helps modulate the HPA axis, lowering cortisol production and supporting emotional balance.

Your gut microbiome plays a key role here — and dietary fibre is its favourite food.

Study spotlight:
A 2016 review in Frontiers in Psychiatry found that prebiotics and probiotics can positively influence the gut–brain–HPA axis by reducing stress-induced cortisol levels and improving mood stability.³

Read More – High Cortisol – The Real Impact of Stress on Your Body

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How Fibre Feeds a Happier Gut Microbiome

Not all fibre is the same. Two main types have distinct effects:

Fibre Type	Description	Main Benefit
Soluble fibre	Dissolves in water and forms a gel-like substance	Feeds good bacteria; balances blood sugar; supports serotonin production
Insoluble fibre	Adds bulk to stool; speeds up elimination	Keeps digestion regular; prevents bloating and sluggishness

When gut microbiome digest soluble fibre (from foods like oats, apples, beans, and flaxseeds), they produce short-chain fatty acids (SCFAs) — particularly butyrate, propionate, and acetate.

These SCFAs:

• Nourish intestinal cells
• Reduce inflammation
• Influence neurotransmitter production
• Support the integrity of the gut barrier (often called the “gut lining”)

A healthy gut lining = less inflammation and a steadier mood.

Read More: The Fibre Fix – Why Women Need Soluble & Insoluble Fibre

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The Science: How Fibre Affects Gut Microbiome, Mood and Mental Health

1️⃣ Higher Fibre = Lower Risk of Depression

Fibre consumption both alone and as part of a healthy dietary pattern has been consistently associated with better mood.⁴

A large study from the National Health and Nutrition Examination Survey (NHANES) found that adults who ate more dietary fibre had significantly lower odds of depression compared to those who consumed the least.

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2️⃣ Gut Microbiome Produce Mood-Boosting Compounds

Certain gut bacteria, such as Bifidobacterium and Lactobacillus, thrive on soluble fibre and produce serotonin precursors like tryptophan.

About 90–95% of serotonin — the “feel-good” neurotransmitter — is made in the gut, not the brain. Fibre literally fuels the microbiome that help your body make serotonin.⁵

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3️⃣ Prebiotic Fibre Reduces Stress Hormones

A clinical trial published in Psychopharmacology gave healthy adults prebiotic fibre (galacto-oligosaccharides) for 3 weeks.⁶

Result: lower cortisol (stress hormone) levels and improved emotional processing — suggesting a calmer, more positive mood.

A recent also study found that an 8-week diet with a high potential prebiotic content improved anxiety, stress, and sleep in adults. The prebiotic diet comprised a minimum of 5 g/d of asparagus, garlic, onion, oats, whole wheat, chickpeas, or watermelon.⁷

Inulins are well-established popular prebiotics, predominantly found in a variety of fruits, vegetables, and wheat. Numerous studies have shown that inulin can stimulate the growth of Bifidobacterium spp. and Faecalibacterium prausnitzii. ⁸

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4️⃣ Better Fibre Intake = More Resilient Gut-Brain Axis

A 2022 review in Frontiers in Nutrition highlighted how dietary fibre improves gut microbiome diversity, strengthens the gut barrier, and reduces systemic inflammation — all linked to a more resilient gut-brain axis and improved mental well-being.

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Fibre, Hormones, and Mood in Women 30+

Women in their 30s and 40s experience fluctuations in oestrogen and progesterone, which can affect serotonin levels, sleep, and stress resilience.

Fibre supports hormone balance by:

• Aiding oestrogen detoxification in the liver and gut
• Reducing reabsorption of excess hormones through the bowel
• Supporting steady blood sugar, reducing energy dips and irritability

A 2018 study in The Journal of Nutrition found that higher fibre intake was linked to lower circulating oestrogen levels, which can help reduce PMS, bloating, and mood swings.⁹

Read More: Feeling constipated?

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Best Fibre-Rich Foods for a Happy Gut & Mind

Here are some great mood-supporting, fibre-rich foods to include daily:

Food	Fibre Type	Approx. Fibre per 100g	Mood Support Benefit
Oats	Soluble	10g	Beta-glucan supports gut bacteria and serotonin
Apples (with skin)	Soluble & Insoluble	2.4g	Contains pectin, a prebiotic fibre
Flaxseeds	Soluble & Insoluble	27g	High in ALA omega-3 and prebiotic fibre
Lentils	Soluble	8g	Stabilises blood sugar and feeds gut microbes
Chickpeas	Soluble	7g	Produces SCFAs for gut and mood health
Psyllium husk	Soluble	80g	Clinically proven to improve gut function
Carrots	Insoluble	2.8g	Adds bulk and aids detoxification
Bananas (ripe)	Soluble	2.6g	Contain prebiotic inulin
Asparagus	Soluble	2g	Rich in prebiotic inulin for gut flora
Sweet potato	Soluble & Insoluble	3g	Supports digestion and oestrogen metabolism

Read More: How to Use Psyllium Husk in Your Diet

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How Much Fibre Do You Need?

Most UK adults only eat 18g of fibre per day, far below the recommended 30g. ¹⁰

To support both gut microbiome and brain health:

• Aim for 25–30g daily
• Include a mix of soluble and insoluble sources
• Increase intake slowly, and drink plenty of water

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Practical Tips to Boost Fibre for a Happier Gut

✅ Add chia or flaxseeds to your breakfast
✅ Choose wholegrain bread or oats instead of refined carbs
✅ Snack on fruit with skins (like apples or pears)
✅ Include beans or lentils in soups and salads
✅ Try prebiotic fibre supplements (like inulin or galacto-oligosaccharides) if you struggle to meet your needs through diet

Read More: 20 Things To Know About Your Gut Microbiome

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Key Takeaway

Your gut and brain are in constant conversation — and fibre is one of the best mediators in that dialogue.

By nourishing your gut microbiome with a variety of fibre-rich foods, you can:

• Improve digestion
• Support hormone balance
• Reduce inflammation
• And potentially boost your mood and emotional resilience

So, the next time you’re feeling low, reach for a bowl of oats, a handful of chickpeas, or a smoothie with flaxseeds — your gut (and brain) will thank you as you feed your friends with benefits.

Fibre, Mood & Gut Microbiome – Frequently Asked Questions

• Drink plenty of water
• Mix soluble and insoluble soources
• Include fermented foods (like kefir or sauerkraut) to help your gut adapt

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Gut Microbiome: Sources

1. Xu, H. et al. (2020). “Association between dietary fibre intake and depression in adults.” Nutritional Neuroscience.
2. O’Mahony, S.M. et al. (2015). “Serotonin, tryptophan metabolism and the brain–gut–microbiome axis.” Behavioural Brain Research.
3. Schmidt, K. et al. (2015). “Prebiotic intake reduces waking cortisol and alters emotional bias in healthy volunteers.” Psychopharmacology.
4. Liang, S. et al. (2022). “Dietary fibre, the gut microbiota, and mental health.” Frontiers in Nutrition.
5. Gaskins, A.J. et al. (2018). “Dietary fibre intake and reproductive hormone levels.” Journal of Nutrition.
6. NHS (2024). “How to get more fibre into your diet.” NHS.uk.

1. The Microbiota-Gut-Brain Axis – PubMed ↩︎
2. Fibre & fermented foods: differential effects on the microbiota-gut-brain axis | Proceedings of the Nutrition Society | Cambridge Core ↩︎
3. Sarkar, A. et al. “The microbiome in psychology and cognitive neuroscience.” Frontiers in Psychiatry, 2016. ↩︎
4. Fibre & fermented foods: differential effects on the microbiota-gut-brain axis | Proceedings of the Nutrition Society | Cambridge Core ↩︎
5. Serotonin, tryptophan metabolism and the brain-gut-microbiome axis – PubMed ↩︎
6. Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers – PubMed ↩︎
7. Fibre & fermented foods: differential effects on the microbiota-gut-brain axis | Proceedings of the Nutrition Society | Cambridge Core ↩︎
8. The Microbiota-Gut-Brain Axis | Physiological Reviews | American Physiological Society ↩︎
9. Association between the adherence to different dietary patterns and sperm chromatin integrity in healthy men – Reproductive BioMedicine Online ↩︎
10. NHS (2024). “How to get more fibre into your diet.” NHS.uk. ↩︎