Participants recruited from the university community in the Southeast U.S. will participate in a randomized, double-blind, placebo-controlled interventional study for approximately 8 weeks following obtainment of informed consent. Participants will be asked to maintain their usual physical activity level as well as their usual diets with the exception of fermented foods, food containing added probiotics (e.g. yogurts with live, active cultures or supplements or probiotic supplements), or foods with added fiber supplements.
After obtaining consent, participants will be randomized to receive either the probiotic or placebo daily for 8 weeks. All study days will be ± 3 days to account for variation in each participant's menstrual cycle. The study supplements will be distributed approximately 7 days before their first menstrual event. Participants will be instructed to begin taking the study supplement 3 days after they menstruate.
At randomization, participants will be asked to start completing daily questionnaires inquiring about gastrointestinal symptoms, abdominal pain as measured by a visual analog scale, duration of abdominal pain, stool form and number, adverse events, and medications taken, including the dose and administration schedule. On the third day of their menstrual cycle (day 3/menstruation 1), they will begin consuming their study supplement (start of intervention). On the days participants experience gastrointestinal symptoms related to the menstrual cycle, they will answer an additional questionnaire asking about gastrointestinal symptoms. Approximately seven days prior to the first menstrual cycle (study day -7) and three days after each menstrual event (study day 3 and 31), participants will answer the Menstrual Symptom Questionnaire to assess symptoms leading up to and during menstruation. Seven days after each menstrual event (study days 7 and 35), participants will be administered the Perceived Stress Scale to assess stress levels over the previous month. Participants will also answer two validated weekly questionnaires inquiring about gastrointestinal symptoms and how symptoms affect quality of life each week they are in the study. Each participant will also complete a 24-hour dietary recall assessment at four points during the study (study day -7, 21, 28, and 35) in order to determine how dietary patterns fluctuate throughout the menstrual cycle. A subgroup of participants will be asked to provide six additional vaginal swab and stool samples and six additional dietary recalls.
A subgroup of 20 participants per arm will also be consented to provide ten stool samples and vaginal swabs during the study (study day -7, 1, 7, 14, 21, 28, 35, 42, 49, \& 56). Participants will be provided with stool and vaginal swab collection kits. Participants will self collect both of these samples and may either collect them at home or may use a restroom in the Food Science and Human Nutrition building to self collect. Coolers will be left outside of the building and in these restrooms for participants to drop off their samples. If social distancing is required during this study, participants will be asked to collect the samples at home and drop them off in a cooler outside of the building to ensure social distancing. This subgroup will also complete additional 24-hour dietary recalls (study day 1, 42, 49, \& 56).
Participants will continue to answer daily questionnaires until the third day of their third menstrual cycle, at which point they will discontinue answering questionnaires and consuming the study supplement. At the conclusion of the study, they will complete the final questionnaire that asks them which supplement they thought they were consuming to assess blinding efficacy. Participants will be instructed to return any unused supplements to the study site after the completion of the intervention.
