Does metabolic compensation explain the majority of less-than-expected weight loss in obese adults during a short-term severe diet and exercise intervention?

International Journal of Obesity (2012) 36, 1472–1478 & 2012 Macmillan Publishers Limited All rights reserved 0307-0565/12 www.nature.com/ijo ORIGINAL ARTICLE Does metabolic compensation explain the majority of less-than-expected weight loss in obese adults during a short-term severe diet and exercise intervention? NM Byrne1, RE Wood1, Y Schutz2 and AP Hills3 OBJECTIVE: We investigated to what extent changes in metabolic rate and composition of weight loss explained the lessthan-expected weight loss in obese men and women during a diet-plus-exercise intervention. DESIGN: In all, 16 obese men and women (41±9 years; body mass index (BMI) 39±6 kg m  2) were investigated in energy balance before, after and twice during a 12-week very-low-energy diet(565–650 kcal per day) plus exercise (aerobic plus resistance training) intervention. The relative energy deficit (EDef) from baseline requirements was severe (74%–87%). Body composition was measured by deuterium dilution and dual energy X-ray absorptiometry, and resting metabolic rate (RMR) was measured by indirect calorimetry. Fat mass (FM) and fat-free mass (FFM) were converted into energy equivalents using constants 9.45 kcal per g FM and 1.13 kcal per g FFM. Predicted weight loss was calculated from the EDef using the 0 7700 kcal kg  1 rule0 . RESULTS: Changes in weight (  18.6±5.0 kg), FM (  15.5±4.3 kg) and FFM (  3.1±1.9 kg) did not differ between genders. Measured weight loss was on average 67% of the predicted value, but ranged from 39% to 94%. Relative EDef was correlated with the decrease in RMR (R ¼ 0.70, Po0.01), and the decrease in RMR correlated with the difference between actual and expected weight loss (R ¼ 0.51, Po0.01). Changes in metabolic rate explained on average 67% of the less-than-expected weight loss, and variability in the proportion of weight lost as FM accounted for a further 5%. On average, after adjustment for changes in metabolic rate and body composition of weight lost, actual weight loss reached 90% of the predicted values. CONCLUSION: Although weight loss was 33% lower than predicted at baseline from standard energy equivalents, the majority of this differential was explained by physiological variables. Although lower-than-expected weight loss is often attributed to incomplete adherence to prescribed interventions, the influence of baseline calculation errors and metabolic downregulation should not be discounted. International Journal of Obesity (2012) 36, 1472–1478; doi:10.1038/ijo.2012.109; published online 24 July 2012 Keywords: metabolic compensation; adaptive thermogenesis; predicted weight loss; resting metabolic rate; energy restriction; exercise training INTRODUCTION A common approach to facilitating weight loss is to reduce energy intake. When determining the expected weight loss from a dietary intervention, the method that is often undertaken is to calculate the energy deficit (EDef) from weight maintenance requirements at baseline; then multiply by the duration of deficit; and then divide the total accumulated deficit by a value such as the Wishnofsky constant (for example, 7700 kcal kg  1).1 However, baseline EDef calculations such as these commonly overestimate the actual weight loss achieved.2,3 Although a lack of adherence is often cited as the primary reason for the shortfall in weight loss,2–4 it is also recognised that biological compensatory responses are elicited when energy restriction is imposed, essentially acting to reduce energy expenditure,5 which in turn reduces the EDef and can reduce the weight loss.6–11 Furthermore, the energy density of weight loss is not uniform, and initial body fat, the magnitude of weight loss and use of resistance exercise or high-protein diets may influence the applicability of the Wishnofsky constant.12 As it is the largest component of total daily energy expenditure, researchers have long been interested in changes to resting metabolic rate (RMR) that accompany energy restriction, and the extent to which variance in RMR may differentiate levels of success in weight-loss interventions. Although there is considerable debate as to whether the change in RMR with weight loss is prognostic of successful long-term weight maintenance,13–16 it is well accepted that RMR decreases substantially during energy restriction even before significant weight loss has occurred.16–18 The seminal research undertaken in the Minnesota SemiStarvation experiment, trials on lean men demonstrated that the decline in RMR was most rapid in the first 2 weeks, indicating that the reduced metabolic activity of the body tissues occurred quickly in response to energy deficiency.19 These adaptive responses are equally evident in obese individuals when energy is restricted, despite them having substantial energy stores.16 To accurately predict the amount of weight loss that is physiologically possible, it requires appropriate accounting for 1 School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia; 2Department of Physiology, Faculty of Medicine, University of Lausanne, Lausanne, Switzerland and 3Mater Mother0 s Hospital, Mater Medical Research Institute and Griffith Health Institute, Griffith University, Brisbane, Queensland, Australia. Correspondence: Professor NM Byrne, School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, Brisbane 4059, Queensland, Australia. E-mail: Received 9 February 2012; revised 2 May 2012; accepted 2 May 2012; published online 24 July 2012 Compensatory responses with energy restriction NM Byrne et al 1473 biological compensatory responses that alter the EDef trajectory during energy restriction. The extent to which metabolic adjustments may explain the less-than-expected weight loss has been examined using RMR data collected in energy balance before and after the weight loss intervention.2,3,20 However, predictions of expected weight loss must account for the reductions in energy expenditure that occur during energy restriction, which are greater than is evident in the weight-reduced energy balance state. Another alteration to daily energy expenditure that accompanies energy restriction is the reduction in dietaryinduced thermogenesis (DIT). DIT is the increase in energy expenditure above resting values as a consequence of digestion, absorption and processing of nutrients, as well as the associated sympathetic nervous system response.21 Even without any improved metabolic efficiency in DIT (that is, reduced thermogenesis per calorie ingested) during energy restriction, a modest to severe reduction in energy intake will result in a meaningful absolute decrease in DIT, particularly for individuals with a large habitual energy intake. Without accounting for this reduction in energy expenditure, the expected weight loss during energy restric (...truncated)