Abstract
The composition of weight change has a large impact on energy balance calculations. Composition of long‐term weight change interventions is well‐documented, but information on short‐term weight change under unrestricted free‐living conditions is limited. The composition and energy density of the changes in body weight during 2‐week free‐living conditions were analyzed in adults from two cohorts: cohort 1 (n = 24) included participants from the reproducibility subset of the Observing Protein and Energy Nutrition study; cohort 2 (n = 22) included participants who were studied under free‐living conditions in an ongoing study in the Chicago area. Change in body weight, total body water (TBW) by stable isotope dilution (cohort 1), and fat mass (FM) and fat‐free mass (FFM) by serial DXA (cohort 2) were measured. To determine the fractional composition of the change in body weight we analyzed the linear associations between changes in body weight and changes in body composition. In the combined dataset, the average change in body weight (0.26 ± 1.2 kg) was consistent with being in energy balance. Average change in body weight was associated with the change in TBW (P < 0.0001) in cohort 1 and the change in FFM (P = 0.0002) in cohort 2. A unit change in body weight was composed of 84% change in FFM in the combined dataset indicating that 2‐week fluctuation in body weight is largely composed of FFM. The energy density of 1–3 kg short‐term changes in body weight averaged 2380 kcal/kg.
Highlights
Energy balance, as summarized by the energy balance equation, is described by three terms; energy intake, energy expenditure, and change in body energy stores (Hall et al 2012)
Analysis of body weight of participants from both cohorts indicated a within subject 2-week weight change and standard deviation of 0.18 Æ 1.1 kg in cohort 1 and 0.35 Æ 1.3 kg in cohort 2
We demonstrated that short-term variations in body weight in subjects who are not making an effort to lose or gain weight were largely composed of changes in fat-free mass (FFM) and its major compartment of water
Summary
As summarized by the energy balance equation, is described by three terms; energy intake, energy expenditure, and change in body energy stores (Hall et al 2012). Changes in body energy stores and energy balance can be calculated by subtracting energy expenditure from energy intake (Schoeller and van Santen 1982; Kempen et al 1995; Racette et al 1995). Under a slightly different set of conditions where energy intake is controlled, such as in inpatient studies or outpatient studies where the research team supplies all foods, energy expenditure can be calculated from energy intake and change in body energy stores.
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