Does flavour-nutrient inconsistency compromise energy regulation in humans?

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The modern invention of processed foods has fundamentally changed our food environment. Retailers now stock an extremely wide range of foods. Even single types of food (e.g., pizza) are now available in numerous varieties that differ in size and the number of calories that they contain. For example, our data show that the number of calories in fish pie 'ready meals' can vary by up to 450% in the UK. In animals, this kind of 'variability' promotes overeating and an increase in body weight. For the first time, this project will explore whether this also happens in humans. There are two ways in which variability in our food environment might increase the number of calories that we consume. These are summarised below. In PHASE 1 we will look at our capacity to 'compensate' for calories in food. When we consume one meal shortly after another then good compensation occurs when the size of the first meal controls the size of the second meal (i.e., a larger first meal causes people to consume a smaller second meal). In animals, poor compensation has been linked to a degraded 'cephalic-phase response.' This anticipatory response governs appetite and represents a series of physiological changes (e.g., salivation and insulin release) that prepare the body for the consumption and digestion of food. Critically, merely looking at or smelling a food is sufficient to elicit a response that is proportional to the calories contained in a food. This shows that learning is involved and that responses are based on previous encounters with individual foods. In this phase we will determine whether the cephalic-phase response is reduced in highly variable foods and whether this promotes poor compensation leading to overconsumption. Cephalic-phase responses will be measured in a number of ways. In particular, we will develop a new method based on changes in skin temperature near to the liver. Previously, researchers have found that this 'thermogenic response' is particularly sensitive to different foods. In this interdisciplinary project we will work with an expert in sensor technology to develop this sensitivity still further. In PHASE 2 we will explore the idea that variability in our food environment makes it more difficult for us to predict the extent to which a particular food will stave off hunger. In 2002 a Nobel Prize was awarded for advances in the field of behavioural economics. This work shows that uncertainty tends to generate cautious and conservative responses and has been used extensively to predict animal behaviour and a range of decisions relating to gambling, financial trading, and risk taking. We find it surprising that 'prospect theory' has not been applied to understand dietary behaviour in humans. For the first time, we will draw on these principles to test the idea that our variable food environment causes uncertainty about the effects of consuming a food, which creates confusion and a concern that hunger might be experienced after it has been consumed. In response to this uncertainty we make conservative dietary decisions and select and then consume larger portions of food. In summary, this project will address important questions relating to variability in our dietary environment. Previously, this issue has been largely overlooked. Nevertheless, research in animals would suggest that variability has the potential to play an important role in promoting overeating and obesity. The beneficiaries of this project are wide ranging. For individual consumers, this might involve increased public awareness of the effects of variable foods. For children, guidelines and/or legislation might be introduced to limit exposure to highly variable foods. For obese individuals, interventions might be possible that re-train sensitivity to the calories contained in specific foods. As such, this work has considerable potential to impact a number of groups, including; health professionals, policy makers, educators, and the wider public.