Award details

Palatability satiety and the stimulation of appetite: a role for learning

Reference	BB/D521622/1
Principal Investigator / Supervisor	Professor Martin Yeomans
Co-Investigators / Co-Supervisors
Institution	University of Sussex
Department	Sch of Psychology
Funding type	Research
Value (£)	323,287
Status	Completed
Type	Research Grant
Start date	01/10/2005
End date	30/09/2008
Duration	36 months

Abstract

Previous research has established that the orosensory-reward mechanisms underlying palatability-induced short-term over-eating induced by flavour manipulation counter-act satiety. Further research has established two learning mechanisms which can independently enhance liking for flavours: flavour-consequence learning where the flavour acts as a signal for post-ingestive consequences, with liking changing depending on the hedonic significance of the consequence, and flavour-flavour learning where liking change is generated by association with a second, hedonically-significant flavour. However, to date no study has examined whether enhanced liking for flavours induced by either learning mechanisms results in an acquired ability for that flavour to stimulate appetite. The aim of this project is therefore to examine acquired liking as a cause of short-term over-eating. In particular, the project contrasts hedonic changes induced by the two learning mechanisms, to examine whether the impact of acquired liking on appetite differs depending on the nature of the underlying association. The project is divided into three inter-linked phases, with distinct objectives within each phase. A total of 9 experimental studies are described which sequentially address different aspects of the relationship between acquired flavour liking and control of meal-size in normal weight human volunteers. Studies in phase 1 validate recent research confirming acquired sensory control of meal size depending on carbohydrate-based relative differences in energy density between variants of a food as a model of flavour-consequence learning, contrasted with flavour-sweetness associations. These studies will provide clear tests of the relationship between acquired liking and orosensory control of meal-size, and allow a contrast of the two learning mechanisms. Since obesity is more associated with over-consumption of savory foods, the second phase of studies extends these approaches to examine consequences based on energy differences derived from fat content, and savory flavour differences. This phase also includes two studies which will explicitly examine how these two learning mechanisms interact, since most foods associated with over-eating combine the potential for both forms of learning to occur together (for example a flavoured sweetened food with high energy density could become liked as a consequence both to innate sweetness preferences and post-ingestive effects on metabolism). Both phases 1 and 2 will use normal-weight men with no history of dieting to establish the fundamental nature of short-term over-consumption as a consequence of acquired flavour liking. Phase 3 switches attention to groups more liking to show over-eating in real-life, and who are at risk of weight gain, to test whether disruption in the learning processes underlying acquired flavour liking might explain some of the individual differences in tendency to gain weight through over-eating. The basic format of studies will be the same as in the earlier phases, but here participants will be women characterised according to their past dieting history and self-reported tendency to over-eat. Past research has suggested that women who score high on measures of tendency to diet show impaired flavour-flavour learning, while women who self-report over-eating show heightened sensitivity to manipulated palatability. Both these findings suggest that the ability of acquired liking to modify control of meal-size will also vary depending on these attitudes to eating, and the proposed studies will test this. Overall, the programme will clarify the role of acquired flavour liking in short-term over-eating, and so enhance our understanding of the role of acquired flavour liking in the development of obesity.

Summary

Although most people are born to like sweet tastes, all of our other food preferences are the consequence of our learning about foods. We have come some way in gaining an understanding of some of the mechanisms about how we learn to like new flavours, but we still are some way from fully understanding the relationship between learning and how we control our eating. Two different learning mechanisms in particular are seen as important in flavour preference development. The first mechanism is through our bodies making connections between what a food or drink tastes like (its flavour) and what happens after we have consumed that item. So if we eat a food which gives us energy afterwards, we are thought to link the flavour and the consequence, and we then come to like that flavour. The second mechanism is based on a wider psychological principle that we come to like or dislike new experiences if they happen alongside something else we already like or dislike. So applying this idea to food flavours, if we experience a new flavour with a sweet taste, we come to like the flavour on its own. We also know a great deal about how our immediate liking for a food alters our appetite, and causes us to eat more. The flavour of the food triggers off reward mechanisms in the brain which both give us the experience of liking and make us want to eat more. However, what we do not know is how the learning which underlies our development of food preferences relates to the ability of flavours to stimulate our appetite. The overall aim of this research is to make this link. Using a series of carefully designed and controlled experimental studies with human volunteers, we will use both liked tastes and flavours, and the consumption of carbohydrates and fats, to alter participants liking for flavours, and will then see how this altered liking affects their appetite in controlled tests. This information will be crucial to our understanding of the causes of over-eating. In particular, it is generally accepted that eating too much fat can lead of obesity, but since our liking for the flavour of fat is itself learned, it may be that the learning which underlies liking for fats is critical to over-eating. These studies will establish clearly how acquired liking relates to over-eating, and give important insights into the fundamental role of learning in food preference development. We also know that dieting is difficult and that attempts to diet often fail. Some recent research suggests that dieting itself may alter our ability to learn about flavours, making this type of learning more difficult. This is important if we try to replace liking for foods which may be bad for our health with healthier food preferences. It is also noteworthy that despite a worldwide increase in the incidence of obesity and overweight, many individuals seem able to resist the temptation to over-eat and so do not develop a weight problem. Identifying what makes some people more prone to over-eating is therefore very important. The final part of the proposed research will look at how differences in ability to learn about foods may contribute to differences in tendency to over-eat. Overall this work should contribute greatly to our understanding of how we grow to like flavours, and how this acquired liking may lead to overeating and help explain the current obesity epidemic.

Committee	Closed Committee - Agri-food (AF)
Research Topics	Diet and Health, Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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