Effects of Urolithin A Supplementation on Glucose Metabolism in Healthy Adults 55 >= Years Old: A Randomized Triple-Masked Controlled Clinical Trial

* INCLUSION CRITERIA: In order to be eligible to participate in this study, an individual must meet all of the following criteria: * Provision of signed and dated informed consent form. * Stated willingness to comply with all study procedures and availably for the duration of the study. * Male or female, age \>= 55 years. * Able to speak and read English. (We do not have ready access to interpreters of different languages at the NIA Clinical Unit). * BMI \>= 27. * Ability to take oral medication and be willing to adhere to the daily regimen. * Ability to perform walking and treadmill tests without physical limitations. * In good general health, as evidenced by medical history/physical exam/laboratory results. EXCLUSION CRITERIA: An individual who meets any of the following criteria will be excluded from participation in this study: * History of diabetes requiring treatment with any glucose lowering drug(s). * Fasting glucose \>= 126 on screening visit. * Is on treatment with an investigational drug or other intervention within 8 weeks of enrollment. * Hospitalization within 12 months for myocardial infarction, coronary revascularization or bypass surgery or stroke. * History of autoimmune disease, e.g., Hashimoto s thyroiditis, Myasthenia Gravis or Rheumatoid Arthritis. * Uncontrolled thyroid disease. * Chronic liver disease indicated by medical history or one of the liver enzymes greater than 2 times the normal range. * History of chronic kidney disease or GFR \<60 mL/min/1.73 m\^2. * Anemia (defined as hemoglobin level \<12 g/dl for men or \< 11 g/dl for women). * Poor venous access. * Uncontrolled hypertension as judged by the Investigator. * History of significant GI disease, e.g., IBS, Crohn s disease. * Active cancer or has had treatment for cancer in the last 1 year. * Medical condition requiring absolute and continuous need for long-term treatment with antibiotics, corticosteroids, immunosuppressors. * Currently pregnant or a nursing mother due to possible changes in hormones and metabolism. * History of, or laboratory evidence of HIV virus infection at Screening Visit. * History of, or laboratory evidence of Hepatitis B or C at Screening Visit. * Positive urine drug screen at Screening Visit (unless taking prescribed medication and at the discretion of the PI). * Reports claustrophobia and/or is not eligible to have an MRI as per the MRI eligibility form. * Weight \>= 300 lbs (MRI scanner weight limit). * Hip or knee replacement or other medical condition that prevents MRI research scans from being performed. * Diagnosed with cognitive impairment that clearly prevents the participant from providing informed consent. * Current smoker or tobacco use in the past year. * History of substance abuse, including marijuana use in the past year. * On average, consumes more than 1 alcoholic drink per day. * Any other condition which in the investigator s opinion may adversely affect the subject s ability to complete the study or its measures or which may pose significant risk to the subject.