The goal of this Interventional study is to validate the Smart Underwear device's ability to detect lactose intolerance by comparing its results to self-reported symptoms in adult participants aged 18 and above, divided equally between self-reported lactose-tolerant and lactose-intolerant individuals.

The main questions it aims to answer are:

Can the Smart Underwear device reliably measure flatus events after lactose consumption? Does the Microbiome Activity Index differentiate between responses to lactose and sucrose consumption?

Researchers will compare participants consuming lactose (experimental arm) with their results after consuming sucrose (placebo arm) to see if the device detects increased flatus events and higher Microbiome Activity Index values in the lactose arm.

Participants will:

• Follow a low-fiber/low-FODMAP diet for four days.
• Record meals using a food log and a custom smartphone app.
• Wear the Smart Underwear device for 8 hours daily for three days.
• Fast for 12 hours overnight, consume 20 grams of either lactose or sucrose dissolved in water, and continue fasting for an additional 4 hours.
• Fast for 12 hours overnight, consume 20 grams of the carbohydrate they did not consume the first time (lactose or sucrose) dissolved in water, and continue fasting for an additional 4 hours.
• Complete digestive symptom surveys after each carbohydrate intake.

The randomized crossover design ensures that participants consume both lactose and sucrose on separate days, with blinding maintained for both participants and researchers.

Inclusion Criteria:

• Has no gastrointestinal disorders
• Not consuming any prescribed medications
• Willing and able to consume sucrose and lactose
• Determined to be lactose tolerant or lactose intolerant after completing an eligibility survey

Exclusion Criteria:

• Younger than 18 years old
• Diagnosed with or suspected to have the following conditions: diabetes, prediabetes, high blood sugar, IBD, SIBO, or a food allergy to sucrose or lactose
• Experience gastrointestinal pain, bloating, or diarrhea when consuming garlic, onions, or leeks
• Routinely experience constipation or painful constipation
• Have ever had an anaphylactic reaction after eating or drinking anything

The following Individual Participant Data (IPD) will be shared: Microbiome Activity Index measurements from both the sham control and lactose challenge arms, collected via the Smart Underwear device's electrochemical sensor array during the controlled crossover trial. The Microbiome Activity Index reflects the quantified hydrogen gas events exceeding baseline threshold during the monitoring period. The study protocol and informed consent documents will also be made available. The data represents measurements taken over 8-hour periods following oral lactose or sham administration while participants wore the device.