Abstract
Diet-induced weight loss (WL) is associated with reduced resting and non-resting energy expenditure (EE), driven not only by changes in body composition but also potentially by adaptive thermogenesis (AT). When exactly this happens, during progressive WL, remains unknown. The aim of this study was to determine the timeline of changes in RMR and exercise-induced EE (EIEE), stemming from changes in body composition v. the presence of AT, during WL with a very-low-energy diet (VLED). In all, thirty-one adults (eighteen men) with obesity (BMI: 37 (sem 4·5) kg/m2; age: 43 (sem 10) years) underwent 8 weeks of a VLED, followed by 4 weeks of weight maintenance. Body weight and composition, RMR, net EIEE (10, 25 and 50 W) and AT (for RMR (ATRMR) and EIEE (ATEIEE)) were measured at baseline, day 3 (2 (sem 1) % WL), after 5 and 10 % WL and at weeks 9 (16 (sem 2) %) and 13 (16 (sem 1) %). RMR and fat mass were significantly reduced for the first time at 5 % WL (12 (sem 8) d) (P<0·01 and P<0·001, respectively) and EIEE at 10 % WL (32 (sem 8) d), for all levels of power (P<0·05), and sustained up to week 13. ATRMR was transiently present at 10 % WL (-460 (sem 690) kJ/d, P<0·01). A fall in RMR should be anticipated at ≥5 % WL and a reduction in EIEE at ≥10 % WL. Transient ATRMR can be expected at 10 % WL. These physiological adaptations may make progressive WL difficult and will probably contribute to relapse.
Highlights
Obesity, owing to its high prevalence, associated co-morbidities and large socio-economic costs[1], is probably one of the largest public health problems of the 21st century
A total of thirty-three Caucasian participants started the study and thirty-one were included in the analysis
Our findings show a significant reduction in RMR (10 (SEM 2) %) by the time 5 % weight loss (WL) (12 (SEM 8) d) was reached, with no further reduction up to 16 % WL, which is in agreement with previous research[33]
Summary
Obesity, owing to its high prevalence, associated co-morbidities and large socio-economic costs[1], is probably one of the largest public health problems of the 21st century. The reduction in nonresting EE seen with WL seems to be accounted for mainly by a reduction in exercise-induced EE (EIEE)(8,9), probably owing to increased efficiency[10], given that physical activity (PA) levels have been shown to increase or not to change with sustained WL[11,12]. The extent to which these different, but inter-related, physiological mechanisms are important remains controversial Combined, these mechanisms may act to reduce WL rate and increase the risk of weight re-gain[7]. The primary aim of this study was to determine the timeline over which changes in EE variables (RMR, EIEE and AT) occur during progressive WL with a very-low-energy diet (VLED). A secondary aim was to assess whether this timeline was modulated by sex
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