Lactulose vs Glucose Breath Test: Which Is Best for Detecting SIBO?

When evaluating SIBO, many people ask: lactulose vs glucose breath test—which test detects SIBO best? Both tests measure hydrogen and/or methane produced by gut bacteria after you ingest a sugar substrate, but they work differently. The lactulose breath test uses lactulose, a non-absorbable sugar that travels through the small intestine into the colon, which can help detect overgrowth across a broader segment of the small intestine. The glucose breath test uses glucose, which is absorbed early in the small intestine, making it more focused on proximal SIBO and potentially missing distal sites. Because of these differences, the choice between the two can influence which cases are detected, and some clinicians opt to use both or pair breath testing with additional microbiome insights to build a fuller picture. To see how breath testing fits into a broader gut-health plan, you can explore InnerBuddies’ approach on their product page: InnerBuddies microbiome test. Accuracy and interpretation also vary between the two tests. In the literature, lactulose breath testing often shows higher sensitivity but lower specificity, partly because lactulose can interact with colonic bacteria and transit times to produce what look like positive results. Glucose breath testing tends to be more specific but may miss distal SIBO since the substrate is absorbed early in the small intestine. The presence of methane producers can further complicate interpretation, so many labs report hydrogen and methane to avoid missing non-hydrogen–producing overgrowth. Clinicians typically weigh these results alongside symptoms, medical history, and motility factors, with some opting for sequential or combined testing for a clearer assessment. Timing and comfort are practical considerations in the lactulose vs glucose breath test decision. A lactulose protocol usually requires a longer window—breath samples every 15–20 minutes for about 2–3 hours—and accompanying fasting and dietary prep. A glucose protocol is generally shorter, often around 2 hours with fewer samples. While both tests are non-invasive, the longer lactulose test can feel more burdensome for some patients, particularly if gas and bloating are a prominent concern. Either way, many patients tolerate breath testing well and can plan around the testing schedule. Beyond the test results, InnerBuddies can add a rich layer of interpretation by integrating breath test findings with a comprehensive gut microbiome view. Their modular Gut Health Operating System includes a Gut Microbiome Health Index (0–100) based on an exclusive IP deal with EAFIT University, along with detailed Bacteria abundances, and categorized Bacteria functions to show how you compare to a healthy cohort. Target Group analysis helps tailor insights for specific populations (Healthy Aging, Endurance Sport, Skin & Hair Health, and more), while personalized nutrition and probiotic/prebiotic recommendations translate data into action. InnerBuddies offers gut test solutions directly to consumers as well as to B2B partners, so you can explore the product further at InnerBuddies microbiome test, consider a continuous-guidance option at InnerBuddies Gut Health Membership, or learn how to partner with them at InnerBuddies B2B partner program.