PROJECT SUMMARY Calorie restriction (CR) is a promising nutritional strategy with the potential to slow the aging process. The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trial, funded by the National Institute on Aging, was the first clinical trial to demonstrate the feasibility of achieving sustained, moderate CR in healthy, young and middle-aged adults without obesity. During the 2-year CR intervention, participants achieved 12% CR on average and, compared to an ad libitum intake control group, experienced remarkable improvements in markers of healthspan and a slower rate of biological aging. The overarching goal of this proposed study is to examine whether 2 years of CR results in long-term improvements in the biological, phenotypic, and functional hallmarks of human aging. We hypothesize that exposure to a 2-year CR intervention in early to mid-adulthood results in sustained lower rates of biological aging, delayed manifestations of phenotypic aging, superior indices of functional aging, and greater quality of life compared to ad libitum intake. To test this hypothesis, we will conduct an observational follow-up study of CALERIE participants 10 to 15 years after the end of their trial participation. Participants from the CALERIE CR group will be compared with an ad libitum intake comparison group composed of the CALERIE ad libitum control group and a matched community-dwelling cohort from the Baltimore Longitudinal Study of Aging (BLSA). The well- characterized BLSA cohort is included as a comparison sample to address the concern that the highly screened CALERIE controls may have been healthier than the general population and highly motivated for behavior change. The BLSA also has the rigor, quality control, and several of the same outcome measurements as the CALERIE trial to facilitate comparisons. The proposed CALERIE follow-up study will include a comprehensive set of physical and functional assessments, including resting metabolic rate, body composition, cardiorespiratory fitness, grip strength, and cognitive function, in addition to psychological and quality-of-life measures. Blood and urine also will be collected and analyzed for markers of biological aging and cardiometabolic disease risk. Comparisons will be made between CALERIE CR participants and the combined ad libitum intake comparison group (the CALERIE ad libitum control group and the BLSA cohort). Evaluating legacy effects of the CALERIE trial will determine the effectiveness of a CR intervention in early to mid- adulthood for preventing the development or delaying the progression of age-related chronic disease. The proposed trial will augment the CALERIE data and biospecimen repository for future research to advance our understanding of human aging.

PROJECT NARRATIVE The proposed study is a 10- to 15-year post-trial observational follow-up of CALERIE (Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy), the first randomized controlled trial of calorie restriction (CR) in humans. The CALERIE trial demonstrated that 2 years of CR leads to significant improvements in markers of healthspan and an attenuated rate of biological aging compared to ad libitum intake. With a goal of informing public health strategies that promote healthy aging, the proposed study will examine the legacy effects of the CALERIE trial to determine the effectiveness of CR exposure in early to mid- adulthood in reducing the rate of biological aging and the risk of age-related chronic disease.