If you’ve been dealing with bloating that makes you look six months pregnant, unpredictable digestion, food sensitivities that seem to multiply overnight,  or IBS that never quite improves — you may have heard the term SIBO thrown around. 

First — What Is SIBO?

Small Intestinal Bacterial Overgrowth (SIBO) is a condition where excessive microbes grow in the small intestine, a part of the digestive tract that normally contains relatively low amounts of bacteria. It is not an infection, but an imbalance in our gut microbiome that can cause common IBS symptoms. 

Under healthy conditions:

• The small intestine contains relatively few bacteria
• Most microbes belong in the large intestine
• Food moves steadily downward through coordinated muscular contractions

SIBO develops when this system breaks down.

Importantly, SIBO is not an infection you catch from outside sources.
It is usually a consequence of failed gut defense mechanisms, with the most important being impaired intestinal motility. 

Slow small-intestinal motility disrupts the migrating motor complex (MMC)—the gut’s natural “cleaning wave”—allowing bacteria to accumulate in the small intestine. Contributing factors include:

• Post-infectious injury
  
  • Prior food poisoning (e.g., E. coli, Campylobacter, Salmonella)
    
  • Autoimmune damage to enteric nerve signaling controlling motility 
• Nervous system dysfunction
  
  • Chronic stress or autonomic nervous system imbalance
    
  • Vagus nerve dysfunction
    
  • Neurologic injury (TBI, Lyme disease, mold illness) 
• Hormonal & metabolic conditions
  
  • Hypothyroidism
    
  • Diabetes and blood sugar dysregulation
    
  • Aging-related motility decline 
• Structural or mechanical factors
  
  • Abdominal adhesions (surgery, injury, endometriosis)
    
  • Blind loops or diverticula
    
  • Scar tissue or anatomical obstruction 
• Medications that slow motility
  
  • Opioids and narcotics
    
  • Antiemetics (e.g., ondansetron)
    
  • Long-term acid suppressants (risk-stacking effect) 
• Impaired digestive defenses
  
  • Low stomach acid (hypochlorhydria)
    
  • Reduced bile flow
    
  • Immune dysfunction
    

These factors often overlap, which helps explain why SIBO frequently becomes chronic or recurrent without addressing the underlying motility issue.

Why Does That Matter?

When the movement of food through the gut slows down, this leads to over-fermentation of carbohydrates. Fermentation is the process by which microbes break down sugars to produce energy and proliferate, therefore setting your gut up for microbial overgrowth. This overgrowth then leads to even more fermentation, resulting in increased symptoms. These can include:

• Bloating and abdominal distension
• Gas and belching
• Diarrhea or constipation
• Abdominal pain
• Reflux or nausea
• Early fullness after eating

Many people also experience systemic symptoms such as:

• Fatigue
• Brain fog
• Anxiety or mood changes
• Nutrient deficiencies
• Food fear and restrictive eating patterns

Symptoms are often worse after meals, especially carbohydrate-containing meals.

The Different Types of SIBO

Modern testing shows SIBO isn’t just one condition — it comes in different gas-based subtypes. 

Hydrogen-Dominant SIBO

• Produced by bacteria like E. coli and Klebsiella
• Ferments carbohydrates aggressively
• Commonly associated with diarrhea and bloating

Intestinal Methane Overgrowth (IMO)

Technically caused by archaea rather than bacteria.

• Methane slows gut motility by up to ~50%
• Leads to constipation and incomplete evacuation
• Often involves both small intestine and colon

Intestinal Hydrogen Sulfide Overgrowth (ISO)

The newest recognized subtype.

• Hydrogen is converted into hydrogen sulfide gas
• Can occur in the small intestine and colon
• Often causes severe diarrhea, urgency, or burning GI symptoms

How Is SIBO Diagnosed?

Years ago, diagnosis required invasive sampling of intestinal fluid during endoscopy — a method prone to contamination and rarely practical. Today, the preferred method is breath testing.

Patients drink a sugar solution (usually lactulose), and breath samples are collected over several hours to measure microbial gases:

• Hydrogen
• Methane
• Hydrogen sulfide

Because these gases are produced only by microbes, breath testing acts as a noninvasive window into small intestinal fermentation.

Can Diet Cure SIBO?

This is one of the biggest misconceptions. A therapeutic diet can be used to reduce symptoms, sometimes up to 100%, but this does not mean that the SIBO is gone. The overgrowth is still present, but the microbes are not being supplied with their favorite foods and fermentation is greatly reduced as a result. 

Therapeutic diets are best viewed as tools for:

• Symptom relief
• Quality of life
• Supporting treatment

Common approaches include:

• Low FODMAP diet
• SIBO Specific Food Guide
• Low Fermentation diet
• Biphasic diet

It is important to note that all of these diets are inherently restrictive, which means they are meant to be short-term, and may not be supportive or realistic depending on your personal preferences, food triggers, capacity for implementing a diet, concurring conditions, and where you are at with your relationship with food. Working with a nutritionist to personalize your diet approach to symptom management is a necessity. 

So How Is SIBO Treated?

Effective treatment typically follows 3 core pillars:

1. Reduce Microbial Overgrowth

Using:

• Targeted antibiotics
• Herbal antimicrobials
• Elemental diet therapy (in severe cases)

2. Restore Motility–This is an ongoing process that involves addressing the root cause of the motility dysfunction. Some examples include:

• Supporting blood sugar regulation
• Calming the nervous system
• Enlisting help to support adequate digestion 
  • Prokinetics (motility agent)
  • Digestive Enzymes
  • Stomach acid support
  • Maintain intestinal wall integrity (address leaky gut)
  • Probiotics
• Address chronic inflammation

3. Prevent Relapse

SIBO relapse rates approach two-thirds of patients if underlying causes aren’t addressed.
Maintenance strategies may include:

• Gentle reintroduction of fiber and carbohydrates
• Adequate hydration
• Regular movement
• Ongoing motility support
• Microbiome restoration
• Manual therapy-visceral manipulation, massage therapy

The Takeaway

SIBO is a condition of misplaced microbial activity caused by impaired gut function, not simply “bad bacteria.” When properly identified and treated with a root-cause approach, many people experience significant improvement in digestion, energy, and food tolerance.
If you suspect that SIBO might be behind your IBS symptoms or chronic bloating, reach out to schedule an appointment with one of our nutritionists and explore what the right approach is for you!