Metabolic adaptations during negative energy balance and their potential impact on appetite and food intake

Abstract

1This review examines the metabolic adaptations that occur in response to negative energy balance 2 and their potential putative or functional impact on appetite and food intake. Sustained negative 3 energy balance will result in weight loss, with body composition changes similar for different 4 dietary interventions if total energy and protein intake are equated. During periods of underfeeding, 5 compensatory metabolic and behavioural responses occur that attenuate the prescribed energy 6 deficit. While losses of metabolically active tissue during energy deficit results in reduced energy 7 expenditure, an additional down-regulation in expenditure has been noted that cannot be explained 8 by changes in body tissue (e.g. adaptive thermogenesis). Sustained negative energy balance is also 9 associated with an increase in oregixgenic drive and changes in appetite-related peptides during 10 weight loss that may act as cues for increased hunger and food intake. It has also been suggested 11 that losses of fat-free mass could also act as an orexigenic signal during weight loss, but more data 12 is needed to support these findings and the signalling pathways linking fat-free mass and energy 13 intake remains unclear. Taken together, these metabolic and behavioural compensatory responses to 14 weight loss point to a highly complex and dynamic energy balance system in which perturbations to 15 individual components can cause co-ordinated and inter-related compensatory responses. The 16 strength of these compensatory responses is individually subtle, and early identification of this 17 inter-individual variability may help identify individuals that respond well or poorly to an 18 intervention. 19 388 AUTHORSHIP 389 All authors contributed to the writing and editing of the manuscript. 390 391 ACKNOWLEDGMENTS 392The authors would like to acknowledge Professor John Blundell and Professor R. James Stubbs for 393 their theoretical input when writing this manuscript. 394 395 FINANCIAL SUPPORT 396This research received no specific grant from any funding agency, commercial or not-for-profit 397 sectors. 398 399 CONFLICTS OF INTEREST 400None. 401

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