Introduction: Still Bloated After Doing Everything Right?

You’ve cleaned up your diet. Maybe gone gluten-free, tried low FODMAP, added probiotics, even taken gut repair supplements.

But the bloating won’t budge. Or your bowels swing between extremes. Or meals feel more stressful than nourishing.

If this sounds familiar, you might be dealing with something deeper – and often overlooked by standard gut protocols:

SIBO (Small Intestinal Bacterial Overgrowth) or IMO (Intestinal Methanogen Overgrowth).

These aren’t just fancy acronyms. They’re two of the most common causes of persistent bloating, food reactivity, constipation, and gut-brain symptoms I see in clinic. In this post, we’ll break down what they are, how they’re different, how to spot them, and why the typical ‘kill-the-bugs’ approach often backfires.

What Exactly Are SIBO and IMO?

SIBO occurs when bacteria – even normal, ‘friendly’ ones – overgrow in the small intestine, where they don’t belong. This leads to fermentation of carbohydrates, gas production, and symptoms.

IMO, on the other hand, isn’t technically bacteria. It’s an overgrowth of methane-producing microorganisms called archaea.

Both conditions involve overgrowths – but the gas type, symptoms, and treatments differ.

SIBO vs. IMO: The Key Differences

	SIBO	IMO
Gas type	Hydrogen (H2) or Hydrogen Sulphide	Methane (CH4)
Main symptom	Bloating, diarrhoea, urgency	Constipation, slow transit
Test marker	Rise in hydrogen gas (≥20 ppm)	High methane levels (≥12 ppm)
Treatment	Antimicrobials/antibiotics	Different combination of antimicrobials/antibiotics

How Do These Overgrowths Develop?

They don’t come out of nowhere. SIBO and IMO are signs that your digestive system has been under stress for a while.

Root causes include:
– Food poisoning or traveller’s diarrhoea
– Low stomach acid (common with age, stress, PPIs)
– Poor bile flow or pancreatic enzymes
– Gut motility issues (often vagus nerve related)
– Abdominal surgery, adhesions, or scar tissue
– Thyroid issues or chronic stress
– Frequent antibiotic or antacid use

These disrupt digestion, weaken gut defences, and slow the ‘cleansing waves’ (migrating motor complex) that normally clear bacteria between meals.

Common Symptoms of SIBO and IMO

SIBO tends to show up as:
– Bloating (especially after eating)
– Cramping, belching, reflux
– Diarrhoea or frequent bowel movements
– Nutrient deficiencies (especially iron or B12)

IMO often causes:
– Constipation (hard stools, slow transit)
– Bloating that’s worse later in the day
– Poor response to fibre or magnesium
– Nausea or low appetite

Both can cause:
– Brain fog and fatigue
– Histamine or food sensitivities
– Mood swings and poor sleep
– Skin issues (rosacea, eczema, acne)

Why Most Treatments Fail

The mistake I see most often? Jumping straight into a killing protocol without fixing the root dysfunction.

Typical protocols (like herbal antimicrobials, rifaximin, or elemental diets) often:
– Provide short-term relief but symptoms return
– Cause severe ‘die-off’ reactions from poor drainage
– Disrupt beneficial microbes if not timed properly
– Miss the root cause (e.g. low motility or structural issues)

You can’t starve or supplement your way out of SIBO/IMO without restoring balance and rhythm.

How to Test for SIBO or IMO

Breath testing is the main functional tool:
– Uses lactulose or glucose to track hydrogen and methane gas
– Measures levels every 15-20 minutes for 2–3 hours
– Rise in hydrogen = SIBO
– Methane ≥10 ppm at any point = IMO

Other helpful tests:
– GI-360 stool test: to identify dysbiosis, inflammation, and yeast or parasitic co-infections
– Organic Acids Test: for downstream impacts like nutrient loss, detox strain, or fungal overgrowth

The Functional Medicine Approach (What We Do Differently)

1. Foundations first — Support digestion, sleep, blood sugar, and nervous system regulation
2. Motility support — Use bitters, ginger, or prokinetics to stimulate the migrating motor complex
3. Target the overgrowth — Introduce antimicrobial herbs or medication, based on test results and tolerance
4. Rebuild — Introduce prebiotics and probiotics (when appropriate) to restore diversity
5. Reintroduce — Begin gentle food expansion to increase tolerance, not decrease variety
6. Maintain — Create a lifestyle and rhythm that keeps the gut moving and supported long term

Want to Take the Guesswork Out of Your Gut Plan?

If your gut still feels unpredictable – despite clean eating and good habits – there may be something deeper going on.

SIBO and IMO don’t have to be a life sentence. But they do require a structured, personalised approach.

👉 Ready to stop guessing? Book a free discovery call: https://calendly.com/berkeleynutrition/discovery-call-1