Effect of Low Water Intake on Glucose Regulation Measured Using Continuous Glucose Monitoring

Twenty participants between 18 and 55 will be recruited from San Luis Obispo County using flyers, social media, local channels, and other online methods. Participants must be able to provide written and verbal consent to participate in the study. They must not currently be diagnosed with conditions, including, but not limited to, diabetes, pre-diabetes, pregnancy, and chronic illnesses. They must neither have received any surgery on their digestive tract nor be taking any oral contraceptives.

Surveys will be administered throughout the study consisting of validated surveys, which will be given out to participants via the encrypted data storage intermediary platform RedCap, which creates a unique identifier for each response to a survey and will be used to link responses across the study period for each participant. Participant's personal information will be password-protected and stored separately to be used for follow-up responses by Cal Poly investigators and research staff.

After participants complete the interest form and permit us to contact them, researchers will schedule the first visit to determine if participants are eligible, obtain consent for participation, and complete questionnaires assessing baseline physical activity, fluid intake, and diet. All participant visits will be scheduled through email or in person when the participant is on a prior visit to the laboratory. Any researcher contacting a participant for scheduling will use a Cal Poly email address and will only contact the participant's email provided in the interest form. Any scheduling email sent will follow the attached script. The second visit will occur in person and mark the start of the first six-day intervention. During this visit, researchers will place the continuous glucose monitor and Gene Active sensor and provide participants with resealable containers for urine collection and concealed bags to transport urine samples to the laboratory. Participants will be assigned to treatments in a counterbalanced fashion. For six days, participants will consume either the NAM's recommended total water intake of 2.7 liters per day for women and 3.7 liters per day for men (high water intake group, HWI) or 0.7 liters per day for women and 1 liter per day for men (low water intake group, LWI). Participants will be allowed to consume fluid ad libitum for four days. For the second six days, participants will consume either HWI or LWI, depending on the treatment completed in the first five days. Participants cannot drink fluids other than water and coffee/tea if requested. Water bottles will be provided with the prescribed amount of water for each day. Participants will collect two urine samples daily: a first-morning sample upon waking and an afternoon sample (2:00 PM-5:00 PM). Participants will deliver their urine containers to the laboratory every other day. Urine samples will be analyzed for specific gravity and volume.

In Redcap, participants will complete a daily mood disturbance questionnaire and a weekly solid food-to-water questionnaire. They will also complete daily food fluid intake questionnaires. This will include a urine void survey, where participants will track the number of times they urinated each day. Participants will be asked to align their food intake during the second five-day intervention with the same foods and amounts consumed during the first five-day intervention. During the four-day washout period, participants can eat however they want.