Is susceptibility to weight gain characterized by homeostatic or hedonic risk factors for overconsumption? Physiol

Abstract In any particular group of people-living in the same culture-some gain weight whilst others do not. Overconsumption of food is one factor contributing to this susceptibility to weight gain. Because all individuals are exposed to a similar range of environmental appetitestimulating factors, the variability in overconsumption must be due to variability in intrinsic psychobiological processes. Such variability is an inevitable feature of living organisms. This essay explores whether susceptibility to weight gain is caused by variation in homeostatic processes-such as weak satiety responses to fat, or by hedonic processes-such as hyperresponsivity to the sensory properties of food. The question also arises whether the homeostatic or hedonic processes function separately and independently, or whether they interact. The answer to these questions can throw light upon the organization of behaviours associated with weight control, and can help to develop strategies to prevent weight gain. The theme of this essay was inspired by Gerry Smith's conceptual and experimental work on both homeostatic and hedonic mechanisms implicated in the control of food intake. D 2004 Elsevier Inc. All rights reserved. Keywords: Overconsumption; Weight gain; Hedonic response Susceptibility to weight gain Susceptibility to weight gain is associated with metabolic [1] and behavioural [2] risk factors. Considering metabolic factors, the tendency to gain weight is associated with a low basal metabolic rate, low energy cost of physical activity, a low capacity for fat oxidation, high insulin sensitivity, low sympathetic nervous system activity, and a low plasma leptin concentration. However, when a steady state of obesity occurs, many of these predictors of weight gain are reversed. Behavioural risk factors can exist for energy intake (EI) and energy expenditure (EE) and both can lead to positive energy balance. However, whereas for EE behaviour (physical activity) can account for between 40% and 60% of total EE (depending on the amount of volitional activity, exercise, etc.), behaviour accounts for 100% of EI. Because changes in EI can be of greater magnitude than in EE (on a daily basis), it can be argued that behavioural aspects of EI (i.e., appetite control) constitute risk factors of greater magnitude than those for EE. The behavioural risk factors may be patterns of eating behaviour, hedonic events which guide and reinforce behaviour, the strength of hunger and satiety sensations, or preferences for and selection of particular types of foods. These behavioural risk factors can be regarded as biological dispositions which create a vulnerability for weight gain and which manifest themselves through behavioural acts, or through physiological processes which promote or permit changes in behaviour. It is an important scientific issue whether these behavioural risk factors operate independently of each other or interact. Hedonic response: a risk factor for weight gain? A reasonable proposal is that an exaggerated hedonic response to the sensory features of foods constitutes a behavioural risk factor that could promote excessive EI. Although sedentariness is widespread, there is evidence that weight-gaining individuals do indeed consume excessive amounts of foo