Understanding SIBO: Foods to Include and Avoid for Better Gut

Small intestinal bacterial overgrowth (SIBO) is a condition in which unusually high numbers or the wrong types of bacteria live in the small intestine (1, 2, 3, 4). The small intestine is the long tube in your gut between your stomach and large intestine (colon), and it’s normally low in bacteria. In SIBO, those bacteria grow too much or move into places they shouldn’t. They start fermenting food too early, which creates gas, bloating, pain, and digestive disruption.

It’s not just one simple pattern; SIBO can be of different types (5, 6, 7, 8)

a) Hydrogen-dominant or

b) Methane-dominant

c) Mixed dominant SIBO (Hydrogen and Methane)

d) Hydrogen-sulphide dominant

This depends on what gases the bacteria produce. Recent reviews emphasise that though SIBO has been studied for years, diagnosing and treating it remains tricky (9, 10).

What is SIBO?

The small intestine is designed for digestion and nutrient absorption, while the colon is home to the majority of our gut microbes.

Under normal conditions, several protective mechanisms, including stomach acid, bile, pancreatic enzymes, intestinal motility and the migrating motor complex, help prevent excessive bacterial colonisation of the small intestine.

In SIBO, this balance is disrupted. Excessive numbers of microorganisms are present in the small intestine, where they can ferment carbohydrates before the host has fully absorbed them. This fermentation produces gases such as hydrogen and, in some cases, methane or hydrogen sulfide. The result can be bloating, abdominal discomfort, altered bowel movements and early satiety.

But the problem isn’t simply “more bacteria = more gas.” The type of microorganism, location, underlying motility, intestinal environment and individual’s response all influence the clinical picture. Microbial overgrowth can also interfere with nutrient utilisation and bile acid metabolism and may contribute to changes in the intestinal lining.

That is why treating SIBO effectively isn’t just about “killing bacteria.” The more important question is: why did the small intestine become susceptible to overgrowth in the first place?

Why might this happen? Some common underlying causes include: slowed gut motility, certain illnesses (diabetes, liver disease), low stomach acid, or structural changes after a surgery (11).

Newer studies show that certain kinds of bacteria, like Escherichia coli and Klebsiella pneumoniae, may be more common in the small bowel of people with SIBO and relate to symptom severity (12, 13, 14, 15).

One of the important protective mechanisms against bacterial overgrowth in the small intestine is the migrating motor complex (MMC)—a series of rhythmic contractions that occur during fasting and help sweep residual food, secretions and microorganisms through the stomach and small intestine toward the colon.

This process depends on coordinated activity between the enteric nervous system, smooth muscle and specialised cells called interstitial cells of Cajal (ICCs), which act as important regulators of gastrointestinal motility. Hormonal and neural signals, including motilin, acetylcholine, nitric oxide and other neurotransmitters, help coordinate these contractions.

When intestinal motility or MMC activity is impaired, this housekeeping process may become less effective, allowing greater microbial accumulation and intestinal stasis. This is one reason why impaired motility is considered an important predisposing factor for SIBO.

However, it is important not to oversimplify this relationship: SIBO is not simply caused by “poor MMC” or damaged ICCs.

Motility disorders are one of several factors that can alter the small-intestinal environment and increase susceptibility to bacterial overgrowth.

Similar motility abnormalities can occur in some people with IBS, while in IBD they may be associated with active inflammation, structural changes, strictures or previous surgery.

Therefore, when SIBO keeps recurring, the more clinically relevant question is not just how to reduce the bacterial load, but what underlying factor is allowing microbial overgrowth to occur in the first place?

SIBO symptoms

Symptoms often overlap with those of other gut conditions, which is one reason SIBO is tricky to diagnose. Here are common signs:

• Persistent bloating after meals

• Visible belly swelling or feeling “full” too quickly

• Excessive farting or belching (gas symptoms)

• Abdominal pain, cramps, discomfort

• Changes in bowel habits: diarrhoea, constipation, or alternating types

• Unexplained weight loss or nutrient deficiencies (especially in severe cases)

• Feeling fatigued, or signs of malabsorption (e.g., low B12)

  
  

Because the symptoms can be so similar to (and overlap with) conditions like Irritable Bowel Syndrome (IBS), Celiac disease, or food intolerances, SIBO can be misattributed to the “usual suspects”. A recent review flagged that the hypothesis of SIBO being the cause of many IBS cases remains unproven, and breath tests used for SIBO have serious limitations (16, 17, 18, 19).

SIBO test

When SIBO is suspected, testing helps, but it’s not perfect. The main test is a breath test: you drink a sugar solution (like glucose or lactulose), then breathe into tubes at set intervals. Labs measure hydrogen and/or methane gas levels. If the gases rise early, it could indicate SIBO (24).

However, recent research emphasises major limitations: low sensitivity (misses cases) and low specificity (false positives) with the commonly used lactulose hydrogen breath test (20, 21). The “gold standard” is a direct sample (jejunal aspirate) of fluid from the small intestine, with bacterial counts assessed (22, 23). But it’s invasive, expensive, and not widely used.

So in practice, diagnosis often comes from a mix of clinical symptoms, test results and response to treatment. Always be sceptical if just a breath test is used without considering the full clinical picture.

SIBO treatment

Treating SIBO usually involves a combination of three parts: addressing underlying causes, reducing the overgrowth, and supporting gut health/nutrition. Here’s how.

1. Addressing underlying causes

Without dealing with the root of why bacteria multiplied (slow gut motility, structural gut change, low stomach acid, surgery history), relapse is common. New research confirms that relapses remain a big challenge (24).

2. SIBO diet

Nutrition plays a key role in SIBO management: it helps control symptoms, starve over-growth, and rebuild gut health. Here’s how to approach it.

What Foods to eat for SIBO

• Lower fermentable carbs: Diets like the Low-FODMAP or other gut-directed carbohydrate reduction patterns help reduce gas/fermentation by bacteria.

• Real, minimally processed foods: Whole, cooked foods, lean proteins, cooked veggies (especially while symptoms are active) are easier on the gut.

• Tailored approach: Because each person is different (hydrogen vs methane type, motility issues, etc), diet must be personalised.

Foods to Avoid For SIBO:

Why diet matters for SIBO

• Bacteria feed on certain fermentable carbs; reducing their “food” helps reduce overgrowth and gas.

• The gut lining and motility improve when the diet supports healing rather than constant fermentation.

• A good diet supports the return of a healthy gut microbiome and nutrient absorption.

  
  
  
  

What could SIBO be misunderstood for?

Because symptoms mimic many other gut disorders, SIBO may be confused with or misdiagnosed as:

• Irritable bowel syndrome (IBS)

• Food intolerances (e.g., lactose, fructose)

• Small intestinal fungal overgrowth (SIFO)

• Inflammatory bowel disease (IBD), such as Crohn’s or ulcerative colitis

• Celiac disease or malabsorption syndromes

  
  

Research cautions that diagnosing SIBO based solely on breath tests in IBS patients may lead to overdiagnosis and overuse of antibiotics. It’s important to rule out other conditions, especially when symptoms are severe or unusual (e.g., weight loss, blood in stool, night sweats).

How common is SIBO?

The prevalence of SIBO varies a lot. This is mainly because testing methods differ and underlying populations differ. Some key findings:

• In patients with IBD, SIBO prevalence was about 22.3% in one meta-analysis.

• Although community prevalence in people without gut disease is not clearly defined, among people with chronic bloating or IBS-type symptoms, it may be relatively common.

• Relapse is also common: recent research highlights that, despite treatment, many people relapse because underlying causes aren’t fixed (25).

  
  

In short, SIBO is not rare, especially in people with gut symptoms and risk factors. But it’s not guaranteed to be the cause of every bloating case.

Final thoughts: What you can do now

If you suspect you might have SIBO, here are practical steps:

1. See a gastroenterologist, especially if you have persistent bloating, gas, a change in bowel habits, or nutrient deficiencies.

2. Ask about testing: Breath tests can help. But know their limits; direct aspiration is more accurate but more invasive.

3. Talk about root causes: Slow gut motility, surgery, medications (e.g., proton-pump inhibitors), and structural issues matter. Make sure your doctor explores these.

4. Work with a gut-health nutritionist: Especially someone who understands SIBO and can guide diet transitions (from low-fermentable to maintenance). At Pragmatic Nutrition, we emphasise that “healthy doesn’t mean trendy, it means tested.”

5. Expect maintenance: After initial recovery, you’ll likely need to maintain good eating habits, motility support (exercise, hydration), and periodic monitoring.

6. Be patient: Some people heal quickly, others take months or more.

   
   

Why does this matter for your gut health journey?

At Pragmatic Nutrition, our mission is to help you nourish your body with the right nutrition so you can thrive with energy, balance and lasting wellness. If SIBO is part of your gut story, then understanding these steps gives you control. You’re not simply reacting to symptoms; you’re creating a plan.