Challenges in defining successful adherence to calorie restriction goals in humans: results from CALERIE 2

Authors: CORBY, MARTIN - Pennington Biomedical Research Center; HOCHSMANN, CHRISTOPHER - Pennington Biomedical Research Center; DORLING, JAMES - University Of Glasgow; BHAPKAR, MANJUSHRI - Duke University School Of Medicine; PIEPER, CARL - Duke University School Of Medicine; RACETTE, SUSAN - Washington University School Of Medicine; DAS, SAI KRUPA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; REDMAN, LEANNE - Pennington Biomedical Research Center; KRAUS, WILLIAM - Duke University School Of Medicine; RAVUSSIN, ERIC - Pennington Biomedical Research Center

Submitted to: Experimental Gerontology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2022
Publication Date: 6/1/2022
Citation: Corby, M.K., Hochsmann, C., Dorling, J.L., Bhapkar, M., Pieper, C.F., Racette, S.B., Das, S., Redman, L.M., Kraus, W.E., Ravussin, E. 2022. Challenges in defining successful adherence to calorie restriction goals in humans: results from CALERIE 2. Experimental Gerontology. https://doi.org/10.1016/j.exger.2022.111757.
DOI: https://doi.org/10.1016/j.exger.2022.111757

Interpretive Summary: Calorie restriction has been shown to be helpful in slowing the aging process in humans. However, in studies of calorie restriction, it often is difficult to measure an individual's true calorie intake. Self-reported measures of dietary intake are often inaccurate, and more technical approaches are burdensome and expensive. The CALERIE 2 study tested the effects of a two-year caloric restriction program in adults without obesity and used the measure of body weight to determine if individuals were consuming 25% less calories than needed to maintain body weight. At the end of the two-year study period, most participants were within their expected weight loss zone; however, on average, they only restricted calories by about 12%. The limitations of using weight to assess calorie restriction highlights the challenges faced by researchers when trying to guide and/or monitor individuals following calorie-restricted diets.

Technical Abstract: Background: The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) phase 2 trial tested the effects of two years of 25% calorie restriction (CR) on aging in humans. CALERIE 2 was one of the first studies to use a graph of predicted weight loss to: 1) provide a proxy of dietary adherence, and 2) promote dietary adherence. Assuming 25% CR, each participant's weight over time was predicted, with upper and lower bounds around predicted weights. Thus, the resulting weight graph included a zone or range of body weights that reflected adherence to 25% CR, and this was named the zone of adherence. Participants were considered adherent if their weight was in this zone. It is unlikely, however, that the entire zone reflects 25% CR. Objectives: To determine the level of CR associated with the zone of adherence and if the level of CR achieved by participants was within the zone. Methods: Percent CR associated with the upper and lower bounds of the zone were determined via the Body Weight Planner (https://www.niddk.nih.gov/bwp) for participants in the CALERIE 2 CR group (N = 143). Percent CR achieved by participants was estimated with the intake-balance method. Results: At month 24, the zone of adherence ranged from 10.4(0.0)% to 19.4(0.0)% CR [Mean(SEM)], and participants achieved 11.9(0.7)% CR and were in the zone. Conclusion: The results highlight the challenges of: 1) setting a single CR goal vs. a range of acceptable values, and 2) obtaining real-time and valid measures of CR adherence to facilitate adherence.