Effect of calorie restriction on the free-living physical activity levels of nonobese humans: results of three randomized trials

Abstract

The objective of this study was to evaluate the influence of calorie restriction (CR) on free-living physical activity levels among humans. Data were from three CALERIE phase I site-specific protocols. Participants were nonobese (body mass index = 23.5-29.9 kg/m² adults randomly assigned to 25% CR, low-calorie diet (LCD, 890 kcal/day supplement diet until 15% weight loss, then weight maintenance), or control at Pennington Biomedical Research Center (PBRC); 30% or 10% CR at Tufts University; and 20% CR or control at Washington University School of Medicine (WUSM). Activity was measured at months 0, 3, and 6 (PBRC) and at months 0, 3, 6, 9, and 12 (WUSM and Tufts). Total daily energy expenditure (TEE) by doubly labeled water and resting metabolic rate (RMR) were used to compute activity energy expenditure: AEE = TEE - RMR - 0.1 * TEE. Accelerometry and 7-day recall categorized activities by intensity. At Tufts, the 10% and 30% CR groups experienced significant decreases in AEE at months 6, 9, and 12. At month 6, a larger decrease in AEE was observed in the CR than the control group at WUSM. At months 3 and 6, larger decreases in AEE were observed in the CR and LCD groups than the control group at PBRC. Accelerometry and 7-day PAR did not consistently detect changes in activity categories. CR-associated changes in AEE were variable but, generally, reduced the energy deficit, which would reduce the expected rate of weight loss. Accelerometry and recall did not consistently explain reduced AEE, suggesting that increased muscle efficiency and/or decreased fidgeting accounted for decreased AEE. Inaccuracy of accelerometry and recall also likely negatively affected sensitivity.

Fig. 1.

Design of the CALERIE studies at Pennington Biomedical Research Center (PBRC), Tufts University (Tufts), and Washington University School of Medicine (WUSM). Activity was measured at the time points denoted with X. BL, baseline; CR, calorie restriction; LCD, low-calorie diet.

Fig. 2.

Mean change in physical activity energy expenditure (AEE) over time by site and group. Error bars, SE. A: data from PBRC. B: data from Tufts University. C: data from WUSM. *Significantly different (P < 0.05) within groups. Brackets report P values comparing change in control vs. CR and LCD groups at PBRC and control and CR groups at WUSM. Only within-group change was evaluated from Tufts University data.