Recruitment:~Flyers, emails, and advertisements in local and university newspapers will be used for recruitment of study participants.~Phone screening:~Interested individuals will be contacted via phone by study staff to assess eligibility by asking questions listed in the inclusion and exclusion criteria.~Informed consent:~If the individual is eligible through phone screening, the study staff will read and explain the informed consent to the individual. Informed consent will contain all the information regarding study procedure, compensation, risks and benefits. If Informed Consent is granted, the participant will be contacted through their preferred method of contact (email or phone) to schedule a hydrogen breath test (HBT).~Screening lactose maldigesters via HBT:~Maldigestion will be classified by a rise of breath hydrogen concentration of greater than 20ppm after a challenge dose of 2% commercial milk containing 0.5g lactose per kg body weight. Participants will consume a low-fiber meal and then fast 12 hours prior to HBT. A breath sample will be obtained from participants just before drinking the milk dose. Participants will then consume milk containing 0.5 grams lactose per kilogram body weight. Breath samples will be obtained according to the following schedule: 0 hour (pre dose), 30 minutes, 1 hour, 90 minutes, 2 hours, 3 hours, 4 hours, 5 hours and 6 hours. Participants who exhibit a rise of breath hydrogen concentration of greater than 20ppm between any two timepoints of the 6-hour test will be classified as lactose maldigesters, and will be qualified to enter the intervention portion of the study.~Intervention:~There will be two in-person visits in intervention.~Visit 1:~Participants should fast for 12 hours and avoid consuming water for 3 hours prior to the MRI scanning appointment. On the day of the visit, participants will undergo a safety screening for MRI compatibility as required by the Purdue MRI Facility and Inner Vision West. Prior to MRI scanning, all participants will remove any metal objects and change into medical scrubs provided by the facility. Participants will then consume their first randomized milk containing 0.5 grams lactose per kilogram body weight (Upper limit - 0.5g/kg up to 50g of lactose). Images of the stomach will be obtained at 0 (pre dose/baseline), 10, 30, 60 and 120 minutes using a Magnetom 3T Prisma MRI scanner. Participants will rate their abdominal pain at 0, 30, 60, 90 and 120 minutes.~Visit 2:~There will be at least a 6-day interval between Visit 1 and Visit 2. The same procedure from visit 1 will be followed in visit 2. Participants will consume the second randomized milk containing 0.5 grams lactose per kilogram body weight during this visit.
Cow's milk contains two types of β-casein: A1 and A2. The μ-opioid peptide BCM-7 is released from A1 but not from A2. BCM-7 is associated with slower gastrointestinal transit and hence increased gastrointestinal transit times. Lactose maldigesters reported an increase in abdominal pain due to consumption of milk containing A1 beta-casein as compared to milk containing only A2 beta-casein. The hypothesis of this study is that the differential abdominal pain is due to the differential gastric transit. This is a double-blinded, randomized, controlled trial conducted to determine if the transit of A1 β-casein milk is modified in the stomach as compared to milk with only A2 β-casein.