SIBO 101: Symptoms, Diagnosis and Treatment
- Dr. Tediana Torrens
- Apr 29, 2024
- 7 min read
Updated: 6 days ago
Digestive concerns like bloating, gas, and abdominal pain are incredibly common—but did you know they might be caused by an overgrowth of bacteria or even yeast in the small intestine? In this post, we’ll break down SIBO (Small Intestine Bacterial Overgrowth), IMO (Intestinal Methanogen Overgrowth), and SIFO (Small Intestinal Fungal Overgrowth)—three overlapping yet distinct conditions that can impact your gut health, quality of life, and more.
What Is SIBO?
SIBO occurs when too much bacteria grows in the small intestine—an area where only small numbers of bacteria should exist. While a healthy gut microbiome lives primarily in the large intestine, bacterial overgrowth in the small intestine can lead to a wide variety of uncomfortable and sometimes serious symptoms. These include both digestive symptoms like bloating and non-digestive issues like brain fog and fatigue.
Until recently, SIBO included all types of bacterial overgrowth. Today, however, we differentiate between:
Hydrogen-dominant SIBO (true SIBO)
Methane-dominant overgrowth, now called IMO
What Is IMO?
IMO (Intestinal Methanogen Overgrowth) refers specifically to an overgrowth of methane-producing microorganisms, primarily Methanobrevibacter smithii, which are not bacteria but archaea. While they function similarly in the gut, their behavior, symptoms, and treatment differ from traditional hydrogen-producing bacteria in SIBO.
SIBO vs. IMO: Key Differences
Feature | SIBO (Hydrogen) | IMO (Methane) |
Main Gas Produced | Hydrogen | Methane |
Primary Symptom | Diarrhea & Bloating | Constipation & Bloating |
Other Symptoms | Gas, reflux, heartburn, fullness, nausesa, abdominal pain, brain fog, fatigue | Same as SIBO, but often more severe bloating and constipation |
Microorganism Type | Bacteria | Archaea |
Conventional Treatment | Rifaximin (antibiotic) | Rifaximin + Neomycin (combo therapy) |
What Causes SIBO/IMO?
SIBO and IMO are typically symptoms of other health conditions that affect the protective mechanisms of the gut. To effectively treat SIBO and IMO, it is critical to identify the underlying cause.
Some of the most common causes include:
Long-term use of acid-blocking medications (PPI)
Food poisoning: Thought to cause 2/3 of cases.
Hypochlorhydria: Low stomach acid due to PPIs, H. pylori, gastritis (inflammation of the stomach lining), or stress.
Low digestive enzymes or bile: Due to hypochlorhydria, pancreatitis, gall bladder diseases.
Slow motility: Caused by high stress, hypothyroidism, EDS (Ehler's Danlos syndrome) or hypermobility syndromes, Parkinson's, POTS (postural orthostatic tachycardia syndrome), Lyme disease, autoimmune conditions and certain medications.
Gastroparesis: Paralysis of the stomach.
Diabetes and insulin resistance: These can both lead to gastroparesis.
Ileocecal valve dysfunction: The valve that separates the small intestine from the large intestine.
Structural abnormalities: Caused by surgery, inflammatory conditions like IBD, endometriosis, diverticulitis, cancer
Immunodeficiency: Genetic conditions or caused by medications like steroids.
How Is SIBO/IMO Diagnosed?
The gold standard for SIBO/IMO diagnosis is a small intestine aspirate culture, but this procedure is invasive (requires an endoscopy procedure) and is rarely performed.
The most common method is a lactulose or glucose breath test. After drinking a sugar solution, you breathe into a machine that measures hydrogen and methane levels. Lactulose is the preferred method of testing as it stays in the digestive tract longer. Glucose is readily absorbed and can sometimes miss diagnoses, especially if there is constipation and slow motility of the gut.
Breath Test Results:
Hydrogen rise ≥20 ppm before 90 minutes = SIBO
Methane rise ≥10 ppm at any time = IMO
It’s important to work with a qualified provider to interpret these results, as false positives and negatives are possible.
SIBO with hydrogen sulfide (HS) gas production is another possibility, though is not discussed in this article.
What About SIFO?
SIFO (Small Intestinal Fungal Overgrowth) is another condition that can mimic SIBO, but instead of bacteria, it involves excess yeast or fungal organisms—most commonly Candida species—in the small intestine. This condition is often overlooked, partly because it is more challenging to test for compared to SIBO and IMO.
SIFO Symptoms
Symptoms often overlap with SIBO/IMO and include:
Bloating
Gas
Abdominal discomfort
Nausea
Brain fog
Fatigue
SIFO Causes
Same causes as SIBO and IMO
Recent antibiotic use
Long-term use of acid-blocking medications (PPIs)
Impaired immune function
Chronic stress
Diets high in sugar and refined carbohydrates
SIFO Diagnosis
SIFO can be diagnosed int he same way as SIBO and IMO through specialized testing like small bowel aspirate with fungal culture. More often, however, diagnosis is inferred based on symptoms and medical history. There are some blood and stool tests that can aid in diagnosis, though ultimately these cannot make a diagnosis alone. Currently, no breath test can confirm SIFO, which makes clinical suspicion and careful evaluation essential.
Treatment Options for SIBO and IMO
Antibiotics
SIBO: Treated with Rifaximin
Pros: Effective, fewer systemic effects, supports microbiome balance
Cons: Expensive without insurance
IMO: Treated with Rifaximin + Neomycin
Pros: More effective for methane overgrowth
Cons: Neomycin can increase risk of broader microbiome disruption and C. difficile infection
Herbal Antimicrobials
Herbal treatments can be a great alternative or complement to antibiotics.
Commonly used combinations:
Candibactin-AR and -BR (Metagenics)
Dysbiocide and FC-Cidal (Biotics Research)
Allimax (Allimax Nutraceuticals), added for IMO
Pros: Gentler on the gut, can also address fungal overgrowth like SIFO
Cons: Longer treatment duration (4–8 weeks), more pills to take, stronger "die-off" symptoms
Nutrition
Some diets used to support the treatment of SIBO and IMO are:
Low FODMAP Diet
SIBO Specific Diet
Specific Carbohydrate Diet
Elemental Diet
These diets all help reduce overgrowth by cutting off the food source of these microorganisms. They are also fairly restrictive diets and are not meant for long-term use.
Maintenance Treatment
To prevent the recurrence of SIBO, IMO or SIFO, it is important to diligently support digestion for at least 3 months. This includes:
Digestive enzyme replacement
Stomach acid replacement (Betaine HCl) or digestive bitters
Prokinetic agents that aid in healthy gut motility
Dietary modifications similar to those listed above, though modified to be less restrictive
Bloating Support
While not a treatment, some herbs can help reduce the painful bloating associated with SIBO, IMO and SIFO.
Peppermint Oil
Carminative herbs: Chamomile, Fennel, Ginger
Iberogast: Combination of herbs that support digestion, motility and reduce bloating
It is important to work with a licensed healthcare practitioner to avoid greater harm from improper use of the above treatments.
What Is Die-Off?
As bacteria (or yeast) die during treatment, they release toxins that your body must eliminate. This can cause temporary worsening of symptoms like:
Fatigue
Brain fog
Nausea
Bloating
Diarrhea or constipation
These symptoms typically resolve in 1–2 weeks, though can last longer in some individuals. Using binders (like activated charcoal or bentonite clay) can help mitigate discomfort, though these must be used with care as they can also prevent absorption of other medications or supplements.
Final Thoughts & Next Steps
SIBO, IMO, and SIFO can all cause significant digestive distress and may impact your energy, mood, and overall health. Breath testing, medical history, and a thorough assessment are key to finding the right diagnosis—and from there, the right treatment.
If you're in Palo Alto or the San Francisco Bay Area and are struggling with chronic digestive symptoms, I can help. We’ll create a personalized plan to investigate and address what’s really going on in your gut.
Disclaimer
The information provided in this blog and throughout the website is intended for educational purposes only and should not be considered, or used as a substitute for, medical advice. The content is not meant to diagnose, treat, or cure any medical condition. This blog does not constitute the practice of any medical, nursing or other professional health care advice, diagnosis or treatment. Always consult with a qualified healthcare provider before making any changes to your health regimen or starting new treatments, and never disregard professional medical advice or delay seeking care because of something that you have read on this blog, website or in any linked materials. Your individual needs and circumstances should be evaluated by a medical professional to ensure safe and appropriate care. If you are experiencing a medical emergency, please call 911 or call for emergency medical help on the nearest telephone immediately.
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