Understanding decisions about portion size: The key to acceptable foods that reduce energy intake?

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Researchers have long been interested in the prospect of developing enjoyable foods that are filling yet low in calories. In almost all studies the critical dependent measure has been 'amount eaten' or some other assessment of feelings of hunger and fullness after a particular test food has been consumed. The logic here is that the amount eaten is normally determined by psychological and physiological effects of eating that take place during and towards the end of a meal. This project will 1) challenge this fundamental assumption and 2) show how an understanding of portion-size decisions can help us to identify palatable foods that promote lower energy intake. The first phase of this project will seek evidence that on occasions when we have control over meal size (which we suspect is very often), the most important determinant of food intake is the decision-making that underlies how much is chosen before a meal begins. In so doing, we aim to provide 1) evidence that 'traditional' methods are not best placed to develop foods that reduce energy intake, and 2) a justification for a new approach for asking questions about food characteristics and their effect on decisions about portion size. After establishing the importance of portion-size decisions, phase two will explore the basis on which decisions about portion-sizes are made. Particular emphasis will be placed on modelling the relative importance of liking for the test foods and expectations about how filling they are, focusing on how these factors combine in the mind of a consumer. In so doing, we will be able to propose particular foods that may help to reduce energy intake, and we will deliver new methods that can be used to explore many other foods in future. Finally, it is important to say that we are not proposing that physiological effects of eating play little or no role in influencing energy intake, merely that their role is secondary to portion-size decisions during individual meals. In the longer term, physiological feedback of this kind could be very important. Indeed, we suspect that portion-size decisions are, in part, learned from previous experiences of the filling effects of different foods. The final phase (phase 3) of this project will test this proposition. This research will inform our understanding of the origin of portion-size decisions. This may explain changes that can occur in the acceptability and use of low-energy 'diet foods' after they become familiar to a consumer, and it will highlight ways of 'protecting' against a decrease in acceptability over time.