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

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.

Keywords: Adherence; Calorie restriction; Dietary adherence; Energy intake; Intensive lifestyle intervention; Lifestyle change; Weight graph; Weight loss.

Figure 1.

A sample weight graph is displayed for a hypothetical participant in the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE™) phase 2 trial (CALERIE 2), which tested the effects of two years of CR on biomarkers of aging in humans. The light blue, green, and yellow lines correspond to the 10th, 50th, and 80th percentiles of expected weight trajectories, respectively. The dark blue line depicts the hypothetical participant’s measured weight trajectory. The participant’s starting weight was 70.7 in kilograms. From months 12 to 24, the yellow, green, and light blue lines represent 62.5, 60, and 55.7 kg, respectively. Reprinted from Contemporary Clinical Trials, Vol 32, Issue 6; Amy D. Rickman, Donald A. Williamson, Corby K. Martin, Cheryl H. Gilhooly, Richard I. Stein, Connie W. Bales, Susan Roberts, and Sai Krupa Das; The CALERIE Study: Design and methods of an innovative 25% caloric restriction intervention; Page No. 880, 2011, with permission from Elsevier.

Figure 2.

Percent CR, determined by the Body Weight Planner, at months 12 and 24 for the upper (80th percentile; yellow line) and lower (10th percentile; blue line) bounds of the adherence zone, as well as the 50th percentile (green line). Actual percent CR achieved by participants at months 12 and 24 is depicted by the dark blue squares and was measured with the intake-balance method.

Figure 3.

Percent CR, determined by the Body Weight Planner, at months 12 and 24 for the normal weight BMI category (22.0 – 24.9 kg/m2, Panel A) and the overweight BMI category (25.0 – 27.9 kg/m2, Panel B). The yellow line depicts the upper (80th percentile) and the blue line the lower (10th percentile) bounds of the adherence zone. The green line depicts the 50th percentile. Actual percent CR achieved by participants at months 12 and 24 is depicted by the dark blue squares and was measured with the intake-balance method.