SIBO and IBS: Why Your Bloating Keeps Coming Back

If you’ve been dealing with persistent bloating, stomach pain, constipation diarrhoea, or a growing list of foods you can’t seem to tolerate anymore, or IBS-type symptoms, you’ve probably been given the label “IBS” at some point.

And maybe you’ve tried a low FODMAP diet and felt better for a while. But then the symptoms crept back in, didn’t they? Or perhaps you’re stuck on such a restrictive diet that you’re not sure what you can safely eat anymore.

Here’s what might actually be going on: Small Intestinal Bacterial Overgrowth, or SIBO.

SIBO is increasingly recognised as a major driver of IBS symptoms. And understanding what actually causes it (not just how to manage symptoms temporarily) is the key to getting your gut health back on track for good.

What Is SIBO, Really?

SIBO happens when bacteria that normally live in your large intestine end up overgrowing in your small intestine, where they don’t belong.

Think of your digestive system like a house with different rooms. Your small intestine is supposed to be relatively clean and quiet, with just a small amount of bacteria. It’s designed that way for good reason – this is where you absorb most of your nutrients, and you need that space clear to do the job properly.

Your small intestine stays bacteria-free thanks to three main protective mechanisms:

1. Adequate stomach acid that kills off bacteria as they enter from your mouth
2. Healthy bile flow that has natural antimicrobial effects
3. Regular intestinal movement via something called the migrating motor complex (MMC) – basically a cleansing wave that sweeps through every 90-120 minutes between meals

When any of these break down, bacteria can survive, multiply, and start fermenting your food way too early in the digestive process. That’s when the bloating, pain, and chaos begin.

Why SIBO and IBS Are So Connected

Research now shows that a significant proportion of IBS cases are actually driven by SIBO, particularly if you experience bloating, gas, constipation, or diarrhoea.

Common symptoms that point to SIBO include:

• Bloating that gets worse throughout the day, especially after eating
• Visible stomach distension (you look pregnant by evening)
• Abdominal pain or uncomfortable pressure
• Feeling full very quickly after you start eating
• Excess gas
• Constipation, diarrhoea, or bouncing between the two
• A growing list of food intolerances that seem to trigger symptoms
• Skin issues like rosacea
• Joint pain or fibromyalgia-type symptoms
• Histamine intolerance
• Difficulty digesting fats
• Nutrient deficiencies even though you’re eating well

This explains why so many people with IBS feel better temporarily on restrictive diets, yet symptoms return the moment they try to reintroduce foods. You’re managing symptoms, but you’re not addressing what’s actually causing them.

A Root Cause Most People Don’t Know About: Your Mouth

Here’s something that rarely gets discussed but is genuinely important: many of the bacteria that cause SIBO don’t start in your gut at all. They start in your mouth.

Bacteria like Streptococcus, Staphylococcus, and Klebsiella live in your mouth, throat, and sinuses. Under normal circumstances, your stomach acid neutralises them before they can make it down to your small intestine.

But when you have low stomach acid (something called hypochlorhydria), these oral bacteria survive the journey and set up camp where they shouldn’t be.

Why Stomach Acid Matters (And Why Zinc Matters Too)

This is where zinc comes into the picture. Zinc is essential for:

• Producing adequate stomach acid
• Releasing digestive enzymes
• Maintaining the integrity of your gut lining

Suboptimal zinc levels are incredibly common in people with chronic gut symptoms, and it creates this problematic cycle: low zinc means poor digestion, which allows bacteria to overgrow, which damages your gut lining further, which makes it harder to absorb zinc.

The Role of Digestive Bitters

Digestive bitters can help by:

• Stimulating stomach acid production
• Improving bile flow
• Supporting digestive enzyme release

This helps restore your small intestine’s natural defence system against bacterial overgrowth. However, bitters aren’t appropriate for everyone (particularly certain hydrogen sulphide SIBO patterns), so working with a practitioner is important.

Other Key Root Causes of SIBO

SIBO is rarely caused by just one thing. It’s usually a combination of factors that have created the perfect storm. Here are the main contributors:

1. Impaired Gut Motility

Remember that migrating motor complex I mentioned? It’s like a cleansing wave that moves through your small intestine every 90-120 minutes between meals, sweeping bacteria along and preventing them from settling in.

After gastroenteritis or food poisoning, your immune system can mistakenly start attacking a protein called vinculin that’s involved in this cleansing process. When that happens, gut movement slows down, and bacteria get the chance to overgrow.

This is why so many people can trace their SIBO symptoms back to a bout of severe food poisoning or a nasty stomach bug overseas.

2. Reduced Bile Flow

Bile isn’t just for digesting fats. It also has strong antimicrobial effects. Animal studies have shown that when you block bile flow, SIBO develops. When you restore bile flow, SIBO resolves.

If your gallbladder has been removed, or if you have sluggish bile flow for other reasons, this protective mechanism is compromised.

3. Abdominal Adhesions

Surgeries – including caesarean sections, appendectomies, or any abdominal procedure – can create scar tissue that physically disrupts normal gut movement. Endometriosis and abdominal trauma can do the same thing.

When your intestines can’t move properly, bacteria accumulate instead of being swept through.

Different Types of SIBO (And Why This Matters)

Not all SIBO is the same. There are actually three main types, and they each produce different symptoms and require different treatment approaches:

Hydrogen-dominant SIBO: Causes bloating, loose stools, and diarrhoea

Methane-dominant SIBO: Causes constipation, slow transit, and harder stools (this is now technically called IMO – Intestinal Methanogen Overgrowth – but most people still call it methane SIBO)

Hydrogen sulphide SIBO: Causes bloating with particularly foul-smelling gas, inflammation, strong food reactions, and fatigue

This is why generic SIBO protocols you find online often fail. What works for hydrogen SIBO might make methane SIBO worse, and vice versa.

The Low FODMAP Diet: Helpful, But Not a Solution

If you’ve tried a low FODMAP diet, you’ve probably noticed that it does help reduce bloating and discomfort. That’s because it limits fermentable carbohydrates that feed the bacteria in your small intestine.

But here’s the problem: low FODMAP is not a cure for SIBO.

Why Low FODMAP Isn’t a Long-Term Solution

It doesn’t remove the bacterial overgrowth. It just stops feeding it as much, which temporarily reduces symptoms.

It doesn’t repair gut motility, restore stomach acid, or fix bile flow. All the underlying causes are still there.

Used long-term, it can actually reduce your beneficial gut bacteria, because you’re also restricting foods that feed the good guys in your large intestine.

It may reinforce food intolerances over time, making your diet more and more restrictive.

Low FODMAP works best as a short-term symptom-relief strategy while you address what’s actually causing the SIBO in the first place. It’s a band-aid, not a cure.

Treating SIBO Properly: A Root-Cause Approach

Effective SIBO management isn’t about just killing bacteria. It’s about:

• Reducing bacterial overgrowth safely while leaving your beneficial flora intact
• Addressing oral and respiratory overgrowths (like chronic sinusitis or gum disease) that may be seeding bacteria down into your gut
• Restoring stomach acid and bile flow so your natural defence mechanisms work again
• Supporting the migrating motor complex to prevent bacteria from settling in the first place
• Healing your gut lining so you can absorb nutrients properly again
• Gradually rebuilding microbial diversity with carefully chosen prebiotics and probiotics

This might involve herbal antimicrobials, digestive support (including bitters when appropriate), motility agents, and specific prebiotics and probiotics – all individualised based on your SIBO subtype and your specific situation.

It’s not a one-size-fits-all approach, which is exactly why working with someone who understands the nuances matters so much.

If This Sounds Like You

If you’ve been diagnosed with IBS, if you struggle with persistent bloating, or if you only feel okay when you’re restricting your diet severely, SIBO may be the missing piece you’ve been looking for.

Short-term dietary strategies like low FODMAP can absolutely help manage symptoms and give you some relief. But long-term gut health requires addressing the underlying cause – whether that’s poor digestion, impaired motility, oral bacteria, or a combination of factors.

Proper testing can identify which type of SIBO you have (if any), and a personalised treatment plan can address your specific root causes rather than just masking symptoms.

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