Clinical Research Directory

Inclusion Criteria: * Able and willing to provide written informed consent prior to completion of any study procedures. * Age ≥40 years at the time of consent. * In generally good health, as determined by medical history, medication review, and investigator assessment. * Willing and able to comply with all study procedures, assessments, and study-related restrictions for the duration of participation. * Willing to adhere to the study's lifestyle considerations for the duration of the study (maintain usual diet unless assigned to the diet arm; maintain usual physical activity; avoid non-essential systemic antibiotics; avoid probiotic/prebiotic/synbiotic supplements). * Willing and able to attend all required in-person study visits at Stanford University and complete remote assessments, if applicable. Exclusion Criteria: * Moderate or severe irritable bowel syndrome (IBS). * Current or prior diagnosis of inflammatory bowel disease (IBD), including ulcerative colitis, Crohn's disease, or indeterminate colitis. * Active gastrointestinal disease, including infectious gastroenteritis, colitis, gastritis, recurrent Clostridioides difficile infection, untreated Helicobacter pylori infection, or clinically significant malabsorption disorders (e.g., celiac disease). * Major gastrointestinal surgery within the past 5 years (excluding cholecystectomy and appendectomy), or history of major bowel resection at any time. * Body mass index (BMI) ≥40 kg/m². * Diabetes mellitus. * Hyperthyroidism or uncontrolled hypothyroidism. * Clinically significant renal disease. * Clinically significant hepatic disease or significant liver enzyme abnormalities. * Clinically significant cardiovascular disease. * Autoimmune or systemic inflammatory disease. * Current malignancy or history of malignancy within the past 5 years, excluding adequately treated non-melanoma skin cancer. * Current use of immunosuppressive medications, including systemic corticosteroids, thiopurines, methotrexate, calcineurin inhibitors, biologic agents, or other immunosuppressive therapies. * Receipt of fecal microbiota transplantation (FMT) within the previous 12 months. * Use of systemic antibiotic therapy within 30 days prior to enrollment or anticipated antibiotic use during the study period. * Use of probiotic supplements, prebiotic supplements, synbiotics, or live microbial therapeutics within 30 days prior to enrollment. * Current use or use within the previous 6 months of medications prescribed primarily for weight loss. * Current use of medications known to significantly affect body weight unless the medication and dose have remained stable for at least 6 months prior to enrollment. * Neurodevelopmental, psychiatric, neurological, or neuromuscular disorders that, in the opinion of the investigator, may impair the participant's ability to provide informed consent, comply with study procedures, or complete study assessments. * Current diagnosis of schizophrenia, bipolar disorder, or other severe psychiatric illness that may interfere with study participation. * Current substance use disorder. * Current smoking or nicotine use, including cigarettes, cigars, electronic cigarettes, vaping products, or nicotine replacement therapy. * History of anaphylaxis or severe allergic reaction to study-related dietary components. * Planned major dietary change, initiation of a structured weight-loss program, or initiation of a specialized therapeutic diet during the study period. * Concurrent participation in another interventional clinical trial. * Any other medical, psychiatric, or social condition that, in the opinion of the investigator, could compromise participant safety, study compliance, or interpretation of study outcomes. * Pregnancy or breastfeeding * Known immunodeficiency state, including HIV infection, primary immunodeficiency, active hematologic or solid-organ malignancy under treatment, or other clinically significant immunocompromise, independent of medication use. * Dysphagia or any condition impairing the ability to swallow oral capsules.