Who Is More Likely to Have SIBO in the United States? Profiles and Risk Factors Explained
Small Intestinal Bacterial Overgrowth (SIBO) happens when bacteria grow excessively in the small intestine, where they don’t belong. This can interfere with digestion and cause symptoms like bloating, gas, abdominal pain, diarrhea or constipation. SIBO isn’t rare — it’s commonly found in people with certain health conditions or factors that slow gut motility or alter the normal balance of bacteria.
Below are the main profiles and risk factors that make some people in the U.S. more likely to develop SIBO.
1. People With Digestive Diseases
Certain gastrointestinal conditions are strongly linked to SIBO because they either slow motility or change the gut environment:
Irritable Bowel Syndrome (IBS): Many people diagnosed with IBS also have SIBO — studies show a large overlap between the two conditions.
Celiac Disease: Damage to the small intestine in celiac disease can disrupt normal bacterial balance and motility.
Crohn’s Disease and Other IBD: Inflammatory bowel diseases can create structural changes or inflammation that allow bacterial overgrowth.
People with functional gastrointestinal disorders — like chronic constipation or diarrhea — often have a higher SIBO prevalence than those without symptoms.
2. People With Certain Medical Conditions
Various systemic health issues can increase SIBO risk by affecting intestinal movement, immunity, or gut environment:
Diabetes: Especially when autonomic neuropathy slows digestion.
Hypothyroidism: Slowed metabolism can also slow gut motility.
Liver Disease / Cirrhosis: Impaired liver function influences digestion and bacterial balance.
Chronic Pancreatitis or Pancreatic Insufficiency: Can reduce digestive enzyme activity, impair motility, and predispose to overgrowth.
Immune System Disorders: Conditions like HIV or immunoglobulin deficiencies may reduce immune defenses in the gut.
3. People Who Have Had Surgeries or Structural Abnormalities
Changes to the structure of the digestive tract can slow the passage of food and create pockets where bacteria accumulate:
Gastric bypass or other bariatric surgeries
Intestinal resections or strictures
Scar tissue (adhesions) from previous abdominal surgeries
Diverticula or blind loops created by surgery
Any anatomical disruption that slows content flow through the small intestine increases the risk of bacterial overgrowth.
4. People Taking Certain Medications
Some commonly used medications can increase SIBO risk by slowing gut movement or reducing stomach acid — both of which help keep bacteria in check:
Proton pump inhibitors (PPIs) and other long-term acid suppressors reduce gastric acid that normally limits bacterial growth.
Opioids and some anticholinergic medications may slow gut motility, increasing bacterial stasis.
Repeated or long-term antibiotic use can disrupt the normal balance of gut bacteria, allowing overgrowth in the wrong place.
5. Older Adults
As people age, the risk of SIBO increases. This may be due to:
Natural decline in stomach acid production
Slower intestinal motility
Higher likelihood of chronic diseases
Increased use of medications that affect digestion
Older adults are therefore more likely than younger ones to develop SIBO.
6. People With Slowed Gut Motility or Functional Motility Disorders
Conditions or behaviors that slow the movement of food and waste through the digestive tract can predispose to bacterial accumulation, including:
Gastroparesis (delayed stomach emptying)
Chronic constipation
Systemic diseases that affect nerves or muscles of the gut
7. People With Overlapping Digestive Symptoms
Because SIBO symptoms overlap with many digestive conditions, individuals with persistent or unexplained symptoms — even without a formal diagnosis — may be more likely to have SIBO or a related imbalance. Research shows SIBO appears in people with functional dyspepsia, bloating, constipation or diarrhea even when other conditions are diagnosed.
While anyone can develop SIBO, certain groups in the United States have a higher likelihood based on health conditions, surgeries, medication use, age, and motility issues. People with IBS, celiac disease, Crohn’s disease, diabetes, structural changes in the gut, long-term medication use, or slowed gut motility are among the most common profiles associated with SIBO — and many of these risk factors are routinely seen in American clinical settings.