Why Gas and Fermentation Can Play a Role in IBS Symptoms

The Tummy Clinic | March 23rd, 2026

Many people with IBS notice that their symptoms worsen after certain meals.

Common symptoms include:

bloating
abdominal pressure
discomfort after eating
urgency to use the bathroom

One of the most common contributors to these symptoms is intestinal fermentation.

What fermentation means

When we eat carbohydrates that are not fully absorbed in the small intestine, they reach the colon where gut bacteria break them down.

This process produces gases such as:

hydrogen
methane
carbon dioxide

Fermentation is a completely normal process and an important part of digestive health.

However, in people with IBS, two things may occur.

First, certain foods may produce larger amounts of gas depending on their fermentable carbohydrate content.

Second, the digestive system may be more sensitive to normal amounts of gas.

The role of gut sensitivity

In people without IBS, small increases in gas often go unnoticed.

In IBS, however, the digestive system may interpret that same gas production as pressure, bloating, or discomfort.

This relates to the phenomenon of visceral hypersensitivity, where the nerves of the digestive tract respond more strongly to internal signals.

Because of this, symptoms may arise even when gas production is within normal physiological ranges.

Why dietary strategies sometimes help

Dietary strategies can sometimes reduce symptoms by lowering the amount of fermentable carbohydrates reaching the colon.

One example is the low FODMAP diet, developed by researchers at Monash University.

This approach temporarily reduces certain fermentable carbohydrates to determine whether symptoms improve.

Foods are then gradually reintroduced to identify individual tolerance levels.

The goal is not permanent restriction, but understanding how different foods influence symptoms.

Clinical Perspective by
Dr. Tracey Beaulne, ND
Co-Founder, The Tummy Clinic

Dr. Tracey Beaulne, ND

Co-Founder of The Tummy Clinic, a virtual clinic focused on evidence-based care for Disorders of Gut–Brain Interaction (DGBIs), including IBS. Dr. Beaulne works with patients across Ontario to help them understand and manage complex digestive symptoms using a whole-system approach grounded in modern neurogastroenterology.

Frequently Asked Questions

What to Eat When You Have IBS with Diarrhea: Tips for Relief

Managing IBS with diarrhea can be challenging, but making the right food choices can help. Here’s what works for many people with IBS:

Low FODMAP diet: This dietary approach helps reduce symptoms like diarrhea, bloating, and stomach pain. It involves removing certain foods and gradually reintroducing them to see which ones trigger your symptoms.
Easy-to-digest foods: Stick with foods like plain rice, cooked carrots, zucchini, and lean proteins (e.g., chicken, fish) to ease digestion.
Avoiding triggers: Steer clear of fatty, spicy, or fried foods, as well as dairy and caffeine. These can worsen symptoms for many people with IBS.

If you’re unsure which foods work for you, consulting with a healthcare provider can help you create a personalized meal plan.

What Causes Bloating, Gas, and Stomach Pain in IBS?

Bloating, gas, and stomach pain are common in IBS. These symptoms often result from:

Gas buildup: Undigested food or fermentation in the intestines can cause gas and bloating.
Gut motility issues: In IBS, food may move too quickly or slowly through the digestive tract, leading to discomfort.
Food sensitivities: Certain foods like high FODMAP foods can cause bloating or pain.

Managing these symptoms typically involves diet modifications, stress management, and finding the foods that work best for your body.

How to Manage IBS-Related Constipation

IBS constipation can be tough, but there are ways to improve bowel movements:

Increase soluble fiber: Foods like oats, bananas, and carrots can help soften stool.
Stay hydrated: Drinking plenty of water helps keep things moving.
Exercise regularly: Physical activity helps stimulate digestion.

If these strategies don’t work, gentle laxatives or stool softeners might be considered, but always under the guidance of a healthcare professional.

What Foods Trigger IBS Symptoms?

Certain foods can make IBS symptoms worse, including:

High FODMAP foods: These include foods like onions, garlic, certain fruits (e.g., apples, watermelon), and dairy.
Fatty foods: Rich, greasy foods often cause discomfort for those with IBS.
Caffeine and alcohol: These can irritate the digestive system and increase symptoms like diarrhea or bloating.

By tracking your food intake and symptoms, you can start to identify which foods are causing flare-ups and work toward a personalized plan.

What Causes Constant Constipation in IBS?

Constant constipation in IBS can be caused by:

Low fiber intake
Dehydration: Not drinking enough water can make stool hard and difficult to pass.
Stress: Emotional stress often affects digestion and can contribute to constipation.

If constipation persists despite lifestyle changes, consider speaking with a healthcare provider for further assessment and potential treatment options.

How to Deal with Severe Bloating in IBS?

Severe bloating can occur when:

Gas is trapped in the intestines due to difficulty digesting certain foods or fermentation.
Slow motility: In IBS, the digestive system may move food too slowly, leading to bloating.

To manage bloating, consider reducing high FODMAP foods and incorporating more digestive-friendly meals. Stress management techniques like yoga or mindfulness can also help reduce bloating by calming the nervous system.

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