PROJECT SUMMARY Calorie restriction (CR) is defined as eating a nutritionally adequate diet that is below energy requirements. CR has been studied for almost 100 years and has been found to extend the lifespan and healthspan of numerous species. Further, when tested in young and middle-aged humans, modest CR improves healthspan and slows biological aging. However, adherence to CR has been found to decrease over time, calling into question the long-term viability of this approach. A possible alternative to CR that may have better adherence and acceptability is time-restricted eating (TRE), which involves eating one's food in an 8 to 10-hour period of the day. TRE extends the lifespan of rodents, and based on recent human trials, TRE improved disease risk factors and biomarkers of aging. Further, many benefits of TRE were achieved even when weight loss did not occur. During the parent award (U01 AG073204), we are conducting a planning project to determine the feasibility and preliminary efficacy of CR and TRE, which are being delivered via traditional in-person visits and remotely via mobile health technologies. Data from the planning project will help select the CR intervention and identify if and what type of TRE intervention will be tested in a future 5-year trial. Our project will also provide effect size estimates for aging outcomes to adequately power the 5-year trial. The proposed supplement will support close out funds to complete participants' follow-up appointments, data collection and to ensure safety monitoring on the remaining participants. The supplemental funds are necessary due to unforeseen costs incurred by the study, such as increased participant stipends and marketing costs to enrol eligible participants.