Obesity Abstracts

Background: Changes in body composition following energy restriction are highly variable between individuals, but whether adaptations in biological (resting metabolic rate; RMR) or behavioural (physical activity; PA) components of total energy expenditure (TEE) underlie this variability remains unclear. This study examined if changes in TEE and its components were associated with the rate of weight loss (WL) in women during energy restriction.

Methods: 46 women with overweight and obesity (BMI=29.1±2.4 kg/m²) were randomised to continuous (25% daily energy restriction) or intermittent energy restriction (alternate ad libitum and 75% energy restriction days) until ≥5%WL or up to 12 weeks. At baseline, week-3 and post-intervention, body composition (air displacement plethysmography) and RMR (indirect calorimetry) were measured, while TEE and PA (min/day of sedentary, light and moderate and vigorous physical activity; MVPA) were estimated over 7-days (accelerometry). Adaptive thermogenesis (AT) was calculated as the difference between measured and predicted RMR (calculated using stepwise multiple regression with baseline body composition). Rate of WL was defined as percentage of WL divided by days to post-intervention measurement. Pearson’s correlations were conducted for baseline-to-week-3 changes (short-term) and pre-post-intervention changes (long-term). Dietary groups were combined as no pre-post-intervention differences in PA or body composition existed.

Results: Data on 35 women that reached a WL of 6.0±1.6% in 65±17 days were available for these analyses. No associations existed between long-term changes in RMR (r=−0.084; P=0.629) or AT (r=−0.095; P=0.587) and rate of WL. However, long-term changes in TEE (r=0.501; P=0.002), total PA (r=0.572; P<0.001) and MVPA (r=0.574; P<0.001) were positively associated with rate of WL, while changes in sedentary time were negatively associated (r=−0.552; P=0.001). Short-term changes in MVPA were positively associated with rate of WL (r=0.376; P=0.026), while sedentary time appeared to be negatively associated (r=−0.289; P=0.092).

Conclusions: These data suggest that changes in PA and sedentary behaviour, but not RMR or AT, influenced the rate of WL during dietary energy restriction. Changes in PA were present early on during WL, but individual responses were variable and further research is needed to examine whether changes in PA act as markers of WL success.

Trial-registration:NCT03447600.