Could Your Symptoms Be SIBO?

Small intestinal bacterial overgrowth is one of the most common yet underdiagnosed gastrointestinal conditions. Because its symptoms overlap significantly with irritable bowel syndrome (IBS), food intolerances, and other digestive disorders, many people live with SIBO for years without a correct diagnosis.

This checklist is designed to help you assess whether SIBO might be contributing to your symptoms. While it is not a diagnostic tool, if you identify with five or more of the following symptoms, SIBO is worth investigating with a qualified healthcare provider.

Core Digestive Symptoms

  • Bloating that worsens throughout the day: The hallmark SIBO symptom. You wake up relatively flat and progressively distend as you eat meals throughout the day. This happens because bacteria ferment food as it enters the small intestine, producing gas that accumulates
  • Bloating within 30-90 minutes of eating: Unlike large intestinal fermentation (which takes 4-6 hours to produce symptoms), SIBO-related bloating occurs shortly after eating because the bacteria are upstream, in the small intestine
  • Excessive gas (belching or flatulence): The gas has to go somewhere. Hydrogen-dominant SIBO tends to produce more flatulence, while methane-dominant patterns may cause more belching
  • Abdominal pain or cramping: Gas distension stretches the intestinal wall, activating pain receptors. The pain is typically diffuse rather than localised to one spot
  • Nausea, especially after meals: Bacterial fermentation can produce compounds that trigger nausea. Upper abdominal fullness and nausea after eating relatively small meals is common
  • Diarrhoea (hydrogen-dominant): Hydrogen gas draws water into the intestines through osmotic mechanisms, and bacterial overgrowth impairs normal absorption
  • Constipation (methane-dominant): Methane gas directly slows intestinal transit by affecting smooth muscle contractions. If you are chronically constipated, methane-dominant SIBO (or IMO) should be considered

Nutritional Deficiency Symptoms

Bacteria in the small intestine compete with you for nutrients and can impair absorption. This leads to deficiencies even in people who eat a nutritious diet:

  • Iron deficiency (fatigue, pale skin, weakness): bacteria consume iron before you can absorb it
  • B12 deficiency (numbness, tingling, cognitive issues): certain bacteria metabolise B12 for their own use
  • Fat-soluble vitamin deficiencies (A, D, E, K): bacterial deconjugation of bile salts impairs fat digestion and absorption of fat-soluble vitamins
  • Unexplained weight loss: despite adequate caloric intake, malabsorption can cause unintentional weight loss
Warning sign: If you are supplementing with iron or B12 and your levels remain stubbornly low, SIBO-related malabsorption may be the reason. Supplementation cannot overcome a problem of absorption.

Extra-Intestinal Symptoms

SIBO affects far more than just digestion. The following symptoms result from systemic inflammation, nutrient depletion, and gut-brain axis disruption:

  • Brain fog and difficulty concentrating: bacterial metabolites including D-lactic acid can impair cognitive function. Many SIBO patients describe feeling mentally "cloudy" after meals
  • Chronic fatigue: a combination of nutrient malabsorption, poor sleep (from gut discomfort), and systemic inflammation contributes to persistent exhaustion
  • Joint pain and body aches: increased intestinal permeability (which frequently accompanies SIBO) allows bacterial endotoxins into the bloodstream, triggering inflammatory responses in joints and muscles
  • Skin issues (rosacea, acne, eczema): a study in Clinical Gastroenterology and Hepatology found that SIBO was significantly more prevalent in rosacea patients than in controls, and that eradicating SIBO resolved rosacea in most cases
  • Mood disturbances (anxiety, depression): gut-brain axis disruption, serotonin metabolism impairment, and chronic inflammation all contribute to mood changes
  • Restless legs syndrome: linked to iron deficiency and altered neurotransmitter metabolism associated with SIBO

Pattern-Based Indicators

Beyond individual symptoms, certain patterns strongly suggest SIBO:

  • Fibre makes you worse: while fibre is generally healthy, in SIBO it provides more fuel for overgrown bacteria, often worsening bloating and gas
  • Probiotics make you worse: adding more bacteria when the problem is bacterial overgrowth can temporarily worsen symptoms
  • Symptoms improve with fasting or liquid diets: less food means less substrate for bacteria to ferment
  • History of food poisoning: acute gastroenteritis can damage the migrating motor complex nerves, predisposing you to SIBO
  • History of PPI or antibiotic use: both disrupt the protective mechanisms that prevent small intestinal overgrowth
  • Previous IBS diagnosis without improvement: if standard IBS treatments have not worked, SIBO is a likely underlying cause

Next Steps

If this checklist resonates with your experience, consider requesting a lactulose breath test from your healthcare provider. This non-invasive test can confirm or rule out SIBO and identify whether you have hydrogen-dominant, methane-dominant, or hydrogen sulphide SIBO — which determines the appropriate treatment approach.

GutIQ can help you systematically assess your symptom profile and identify patterns that suggest SIBO versus other conditions. Our assessment evaluates the specific timing, triggers, and associated symptoms that differentiate SIBO from other causes of digestive dysfunction.