SCIENTIFIC THINKING ABOUT WEIGHT CONTROL
An alternative paradigm; The ecological model
Any complete understanding of obesity must take account of the differences both within and between individuals and populations, as well as the moderating physiological adjustments which occur as a result of changes in energy balance. This would mean a more ecological approach to the problem which implies a delicate balance between a wide variety of competing forces. There are three main influences on equilibrium levels of body fat—environmental, biological and behavioural—and these are mediated through fat/energy intake (F/EI) and/or fat/energy expenditure (F/EE), but moderated by physiological adjustments to changes in energy balance.
This model adds the biological, environmental and behavioural influences to an equation whose end point is ‘equilibrium stores’ of body fat. This is a dynamic relationship where fat stores ‘settle’, at least temporarily, until there is some change in components of the equation, after which physiological adjustment occurs, or a new equilibrium, or ‘settling point’, is reached. This paradigm discards the notion of a ‘set point’ for body fat, whereby the body works to achieve and maintain a body fat mass of say 75kg. It also modifies the previous notions of energy balance by specifying the initial aspects of food, exercise, the rate of fat intake and the rate of fat utilisation respectively. Finally, the model incorporates the physiological adjustments which occur with body composition changes and which then bring it back into equilibrium. The components of the model are broken into the mediators (i.e. fat intake and expenditure), influences (environment, biology and behaviour) and the moderators (physiological adjustment).
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