The Mystery of Energy Compensation

Abstract

The received wisdom on how activity affects energy expenditure is that the more activity is undertaken, the more calories will have been burned by the end of the day. Yet traditional huntergatherers, who lead physically hard lives, burn no more calories each day than western populations living in labour-saving environments. Indeed, there is now a wealth of data, both for humans and other animals, demonstrating that long-term lifestyle changes involving increases in exercise or other physical activities do not result in commensurate increases in daily energy expenditure (DEE). This is because humans and other animals exhibit a degree of 'energy compensation' at the organismal level, ameliorating some of the increases in DEE that would occur from the increased activity by decreasing the energy expended on other biological processes. And energy compensation can be sizable, reaching many hundreds of calories in humans. But the processes that are downregulated in the long-term to achieve energy compensation are far from clear, particularly in humans -we do not know how energy compensation is achieved. My review here of the literature on relevant exercise intervention studies, for both humans and other species, indicates conflict regarding the role that basal metabolic rate (BMR) or low level activity such as 'fidgeting' play, if any, particularly once changes in body composition are factored out. In situations where BMR and low-level activity are not major components of energy compensation, what then drives it? I discuss how changes in mitochondrial efficiency and changes in circadian fluctuations in BMR may contribute to our understanding of energy management. Currently unexplored, these mechanisms and others may provide important insights into the mystery of how energy compensation is achieved.

Does eating less or exercising more to reduce energy availability produce distinct metabolic responses?

“…As shown in figure 3, there is little evidence from the literature that exercise interventions per se result in metabolic adaptations, which is in agreement with a meta-analysis by Mackenzie-Shalders et al [47] and the animal literature [48,49]. This arguably makes sense evolutionarily because there is no obvious need to reduce metabolic rate if energy intake continues to match energy expenditure.…”

The energetics of childhood: Current knowledge and insights into human variation, evolution, and health

“…Spend X more calories on habitual physical activity, for example, spend X fewer calories on other metabolic tasks and therefore no extra calories overall. This (re)distribution of energy between individual energy expenditure components-referred to relatively interchangeably as 'compensation' or 'trade-offs'-is well supported in the literature for adults (Careau et al, 2021;Halsey, 2021;Pontzer, 2015a), with trade-offs now also documented for immune activity, physical activity, and growth among children (see Section 6.1).…”

“…How are physiological systems such as insulin signaling involved in adrenarche's lasting metabolic effects? Is TEE constraint regulation a trait that is subject to developmental plasticity? It is notable that there is a high degree of individual variation in how quickly/strongly energetic trade‐offs and energy compensation occur in paradigms such as exercise implementation (Halsey, 2021). Is individual propensity for energetic trade‐offs and strong TEE regulation influenced by early life environmental conditions?…”

Key questions in marine mammal bioenergetics

“…In general, energy allocation to maintenance is prioritised before growth and reproduction ( Costa et al, 1989 ; Soto et al, 2004 ; Wheatley et al, 2006 ; Christiansen et al, 2014b , 2018 ; Kershaw et al, 2021 ; Smith, 2021 ). Compensatory mechanisms, such as metabolic depression, may help cope with energy limitation ( Markussen et al, 1992 ; Rosen and Trites, 2002 ) or periods of high energy demand ( Mellish et al, 2000 ; Shuert et al, 2020 ), although little is known about the drawbacks of such mechanisms ( Halsey, 2021 ). Understanding these priorities is important as many bioenergetic models use researcher-defined rules regarding allocation when energy intake is insufficient to meet an individual’s needs, such as when foraging may be disrupted by a disturbance (e.g.…”