IBS (Irritable Bowel Syndrome): Causes, Symptoms, and Functional Medicine Solutions

Irritable Bowel Syndrome (IBS) is one of the most common digestive disorders in the world.

It affects 10–23% of people globally, about 15–20% of Americans, and roughly 20% of Canadians — meaning nearly one in five people struggles with uncomfortable digestive symptoms that often go untreated. IBS accounts for over three million doctor visits annually and billions of dollars in lost productivity and healthcare costs.

Despite its prevalence, many conventional doctors struggle to treat IBS effectively because they often focus on symptoms rather than root causes. This is where Functional Medicine makes a difference — by addressing the underlying dysfunction in the gut ecosystem rather than just masking discomfort.

What is IBS?

IBS is a functional gastrointestinal (GI) disorder, meaning your digestive system may look normal on colonoscopy or imaging tests but doesn’t function properly. This dysfunction can cause a variety of symptoms, including:

• Abdominal pain or cramping

• Bloating and gas

• Changes in bowel habits: constipation (IBS-C), diarrhea (IBS-D), or alternating (IBS-M)

• Urgency or incomplete bowel emptying

• Distention: a feeling of swelling or “rock-hard” belly

Many people are frustrated because standard tests often appear normal, yet the discomfort is very real. Conventional advice like “eat more fiber” or “take Metamucil” is often ineffective, because the root causes are not addressed.

Functional Medicine, by contrast, treats IBS as a systemic problem — focusing on the gut ecosystem, the gut-brain axis, immune function, and lifestyle factors.

What Causes IBS?

IBS is multifactorial — different people may have completely different triggers. Functional Medicine identifies five main categories that contribute to IBS:

1. Gut-Brain Axis and Nerve Dysregulation

The gut has its own nervous system, called the enteric nervous system, which communicates with the brain. In IBS, this signaling can become hypersensitive, making normal gut activity painful or irregular. Some people may feel severe bloating, cramping, or urgency even when the gut appears normal.

2. Motility Issues

The gut muscles move food through the digestive tract. If motility is too slow, constipation may occur; if too fast, diarrhea may result. Some medications for IBS — like Constella, Prucalopride, or IBSrela — may not work if motility issues are severe or the nervous system signals are disrupted.

3. Food Sensitivities

Even without true allergies, foods like gluten, dairy, soy, corn, and eggs can irritate the gut lining and trigger inflammation. We often uses elimination diets to identify trigger foods.

• Gluten: Found in wheat, barley, rye, and spelt. Even if you test negative for celiac disease, gluten can trigger bloating, gas, or diarrhea.

• Dairy: Lactose and proteins like casein and whey can cause symptoms.

• Other common triggers: soy, corn, eggs, sugar, and highly processed foods.

Eliminating trigger foods often leads to dramatic symptom improvement, and reintroducing foods gradually helps identify individual sensitivities.

4. Gut Microbiome Imbalances

Your gut is home to 100 trillion bacteria — more bacterial cells than human cells in your body. When this ecosystem is out of balance, it can cause IBS symptoms.

SIBO (Small Intestinal Bacterial Overgrowth) occurs when bacteria normally found in the large intestine move up into the small intestine, causing bloating, gas, constipation, or diarrhea. SIBO can be diagnosed using breath or urine tests, and treated with targeted nonabsorbed antibiotics like rifaximin, sometimes combined with neomycin.

Yeast overgrowth can also cause digestive problems, often triggered by antibiotics, steroids, birth control, acid-blocking drugs, high sugar intake, alcohol, or diabetes. Treatment may involve antifungals or herbal remedies.

5. Stress and Lifestyle Factors

Stress doesn’t directly cause IBS but exacerbates symptoms. Chronic stress, poor sleep, sedentary lifestyle, or irregular routines can worsen gut motility and sensitivity.

Mind-body practices like meditation, CBT, hypnotherapy, and gentle exercise can improve symptoms.

6. Nutrients and Toxins

Deficiencies in digestive enzymes, zinc, magnesium, or exposure to heavy metals can worsen gut function. Correcting these imbalances supports gut healing and overall wellness.

Diagnosing IBS

IBS is diagnosed based on symptoms (Rome IV criteria) and by excluding other conditions such as celiac disease, inflammatory bowel disease, or infections.

Some additional tests may help pinpoint causes:

• Colonic transit study: Tracks how food moves through your colon to identify slow or fast transit.

• Anorectal manometry: Measures the function of rectal muscles and nerves.

• Defecography: X-ray or MRI evaluation of stool evacuation.

• Sitz marker test: Swallowing markers to track stool movement and detect constipation patterns.

• SIBO Breath Test: This test measures hydrogen, methane, or hydrogen sulfide gases produced by bacterial overgrowth in the small intestine.

  Different gases can indicate different types of overgrowth and help guide treatment:

  
  

  • Hydrogen: Typically associated with diarrhea-predominant IBS (IBS-D). High hydrogen levels suggest that bacteria in the small intestine are fermenting carbohydrates too quickly.

  • Methane: Often linked to constipation-predominant IBS (IBS-C). Methane-producing bacteria can slow gut motility, leading to constipation and bloating.

  • Hydrogen Sulfide: This gas can cause smelly gas, diarrhea, and bloating, and may indicate a type of bacterial overgrowth that is not detected by hydrogen or methane alone.

These tests provide insight into the underlying dysfunction and allow practitioners to personalize treatment, including targeted antibiotics, dietary changes, or probiotics, rather than just managing symptoms.

Managing IBS

Functional Medicine takes a holistic approach, combining diet, lifestyle, supplements, and targeted therapies to address root causes.

1. Diet and Food Management

Low-FODMAP Diet: Reduces fermentable carbs that feed gut bacteria and cause bloating. Typically done in stages: elimination, reintroduction, and personalization.

Elimination Diets: Identify and remove trigger foods like gluten, dairy, soy, corn, and eggs.

Fiber Management:

• Soluble fiber (psyllium, oats) may improve stool consistency.

• Insoluble fiber may worsen bloating or diarrhea for some individuals.

2. Lifestyle and Stress Management

• Exercise: Walking, yoga, or gentle activity improves gut motility and reduces stress.

• Sleep: Prioritize consistent sleep schedules.

• Mind-Body Practices: Meditation, CBT, or hypnotherapy reduces gut hypersensitivity.

3. Gut Healing and Supplements

Supporting your gut with the right nutrients and supplements can be a key part of an IBS management plan. It’s important to introduce any new supplements under the guidance of a registered dietitian or pharmacist to ensure safety, correct dosing, and compatibility with other medications or conditions.

Digestive Enzymes: Help break down food efficiently while your gut heals, reducing bloating, gas, and discomfort, especially if enzyme production is low or certain foods are hard to digest.

Key Nutrients for Gut Repair: Vitamins and minerals such as zinc, glutamine, vitamin A, and omega-3s support the intestinal lining and overall gut health.

Anti-Inflammatory Herbs: Turmeric and quercetin help reduce gut inflammation, soothe irritation, and promote healing.

Gut Ecosystem Reset: For imbalances like SIBO or yeast overgrowth, a stepwise approach with targeted antibiotics and/or antifungals, followed by probiotics or fermented foods, can help restore healthy gut balance.

Leaky Gut: When the intestinal lining becomes permeable, food particles, bacteria, and toxins can leak into the bloodstream, triggering inflammation. This may worsen IBS symptoms and contribute to fatigue, joint pain, cognitive issues, and skin conditions such as eczema. Healing the gut lining with the right nutrients, supplements, and lifestyle interventions is essential for long-term relief and overall wellness.

4. Medications (When Needed)

Medications may help when lifestyle changes aren’t enough:

• Fiber supplements or laxatives for constipation

• Anti-diarrheals for diarrhea

• Antispasmodics for cramping

• Low-dose antidepressants for gut-brain regulation

• Nonabsorbed antibiotics like rifaximin for SIBO

  
  

Some medications may not work if motility issues or nerve signaling dysfunction persist.

Long-Term Outlook

IBS is chronic but manageable. With a personalized plan, patients can:

• Remove trigger foods

• Restore healthy gut flora

• Repair the gut lining

• Improve overall health and quality of life

Final Words

We now have the science, understanding, and tools to treat IBS effectively. By uncovering the root causes—from food sensitivities and SIBO to yeast overgrowth, motility issues, or lifestyle factors—you can reclaim your digestive health.

Even small changes in diet, supplements, and lifestyle can lead to big improvements in symptoms and overall well-being. The power to heal your gut starts with your next meal, and with the right plan, vibrant health is possible.

If IBS is affecting your comfort, confidence around food, or daily life, personalized nutrition care can make a real difference. As a gut health dietitian specializing in IBS and SIBO, I help clients create sustainable, food-first strategiesto support digestion, reduce bloating, and restore gut balance—without restrictive diets or lifelong medication.

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References

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El‑Salhy, M. (2016). Diet in the pathophysiology and management of irritable bowel syndrome. Cleveland Clinic Journal of Medicine, 83(9), 663–672. https://www.ccjm.org/content/83/9/663.

Irritable bowel syndrome. (n.d.). Merck Manual Professional Edition. https://www.merckmanuals.com/en-ca/professional/gastrointestinal-disorders/irritable-bowel-syndrome-ibs/irritable-bowel-syndrome-ibs

Irritable bowel syndrome (IBS). (n.d.). National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome

Pimentel, M., Park, S., Mirocha, J., Kane, S., & Kong, Y. (2006). The effect of nonabsorbed oral antibiotics (rifaximin) on the symptoms of irritable bowel syndrome. Annals of Internal Medicine, 145(8), 557–563.

Shanahan, F., & Whorwell, P.J. (2005). IgG-mediated food intolerance in irritable bowel syndrome: A real phenomenon or an epiphenomenon? The American Journal of Gastroenterology, 100, 1558–1559.

Lin, H. (2004). Small intestinal bacterial overgrowth. Journal of the American Medical Association, 292, 852–858.