Approaches for quantifying energy intake and %calorie restriction during calorie restriction interventions in humans: the multicenter CALERIE study

Abstract

Calorie restriction (CR) is a component of most weight loss interventions and a potential strategy to slow aging. Accurate determination of energy intake and %CR is critical when interpreting the results of CR interventions; this is most accurately achieved using the doubly labeled water method to quantify total energy expenditure (TEE). However, the costs and analytical requirements of this method preclude its repeated use in many clinical trials. Our aims were to determine 1) the optimal TEE assessment time points for quantifying average energy intake and %CR during long-term CR interventions and 2) the optimal approach for quantifying short-term changes in body energy stores to determine energy intake and %CR during 2-wk DLW periods. Adults randomized to a CR intervention in the multicenter CALERIE study underwent measurements of TEE by doubly labeled water and body composition at baseline and months 1, 3, and 6. Average %CR achieved during the intervention was 24.9 ± 8.7%, which was computed using an approach that included four TEE assessment time points (i.e., TEE(baseline, months 1, 3, and 6)) plus the 6-mo change in body composition. Approaches that included fewer TEE assessments yielded %CR values of 23.4 ± 9.0 (TEE(baseline,) months 3 and 6), 25.0 ± 8.7 (TEE(baseline,) months 1 and 6), and 20.9 ± 7.1% (TEE(baseline, month 6)); the latter approach differed significantly from approach 1 (P < 0.001). TEE declined 9.6 ± 9.9% within 2-4 wk of CR beginning and then stabilized. Regression of daily home weights provided the most reliable estimate of short-term change in energy stores. In summary, optimal quantification of energy intake and %CR during weight loss necessitates a TEE measurement within the first month of CR to capture the rapid reduction in TEE.

Trial registration: ClinicalTrials.gov NCT00099099 NCT00099138 NCT00099151.

Fig. 1.

Study timeline and description of 9 approaches for computing average 6-mo energy intake and %calorie restriction (CR). TEE, total daily energy expenditure; DLW, doubly labeled water; BL, baseline; M1, month 1; M3, month 3; M6, month 6.

Fig. 2.

Changes in body weight, body composition, TEE, and resting metabolic rate after 1, 3, and 6 mo of CR.

Fig. 3.

Association between daily change in body energy stores computed from body weight and daily change in body energy stores computed from fat mass and fat-free mass. Body weight and body composition were measured at baseline and after 6 mo of CR. ♦Body weight.

Fig. 4.

Bland-Altman comparisons of %CR computed using the reference approach that incorporated 4 TEE assessment time points with alternative approaches based on 2 or 3 TEE time points. TEE was assessed using the DLW method. %CR was computed using a time-weighted average TEE plus 6-mo change in body composition. Time points included BL, M1, M3, and M6.