When your gut isn’t digesting food right, bacteria can grow where they shouldn’t—like in your small intestine. This condition is called small intestinal bacterial overgrowth, a condition where excess bacteria ferment sugars in the small intestine, leading to bloating, gas, and diarrhea. The lactulose breath test, a non-invasive diagnostic tool that measures gases produced by gut bacteria after consuming a sugar solution is one of the most common ways doctors spot this problem. It’s also known as a SIBO breath test, a type of diagnostic test used to identify abnormal bacterial growth in the small intestine, and it’s simple: you drink a sugar solution, then breathe into a tube every 15 to 20 minutes over a few hours. The test looks for hydrogen and methane gases—byproducts of bacterial fermentation—that shouldn’t be present in high amounts in your breath.
Why does this matter? Because if bacteria are hanging out in your small intestine, they’re stealing nutrients, irritating your gut lining, and causing symptoms that mimic IBS—bloating after meals, diarrhea, cramps, even brain fog. Unlike a colonoscopy, the lactulose breath test doesn’t need sedation or prep beyond fasting. It’s safe, quick, and gives clear clues about what’s happening in your gut. The results show when gases spike: an early rise usually means bacteria are overgrowing in the small intestine, while a later spike might point to normal fermentation in the colon. Doctors use this timing to tell the difference between SIBO and just slow digestion.
People who’ve tried probiotics, eliminated gluten, or cut out FODMAPs but still feel awful often end up here. The test helps cut through guesswork. It’s not perfect—false positives and negatives happen—but it’s one of the few tools that actually shows what’s going on inside your gut without surgery. If you’ve had unexplained digestive issues for months or years, this test might finally give you an answer. Below, you’ll find real-world insights from people who’ve been through it, what the results mean, and how to follow up with treatment.
SIBO causes bloating, gas, and digestive issues. Breath tests are the most common way to diagnose it, but they’re not perfect. Learn how testing works, why results can be misleading, and what treatments actually help-plus how to prevent it from coming back.
