Taste and appetite

Abstract

In this short paper, I discuss two interpretations of the implications of food reward for healthy eating. It is often argued that foods that are palatable and provide sensory pleasure lead to overeating. I discuss an example of an experiment that claims to demonstrate this, to many people, intuitively reasonable result. I point out a number of assumptions about reward and eating behaviour underlying this sort of thinking and ask whether overeating might not instead, to a large extent, result from avoiding reward and sensory satisfaction. Four different experimental results that support the suggestion that 'quality can replace quantity' are briefly reviewed. Humans eat foods, not nutrients. Homeostatic appetite mechanisms based on nutrients are therefore not sufficient to explain human food behaviour. Also, if homeostatic mechanisms were the only determinants of food intake, the recent problems of overeating and obesity would be hard to explain. Other control systems of ingestive behaviour and energy balance have therefore been identified [1]. These systems deal mainly with motivational, cognitive and emotional aspects of eating behaviour. Rewards derived from eating figure strongly in these extensive neural networks. Sensory pleasure from the taste of foods is therefore a major determinant of food intake. Eating is initiated when a state of hunger is reached, but under most circumstances, not just any food will do; usually, people experience hunger for particular foods under particular circumstances. Since foods provide reward [2], it is important to understand the processes of hedonic eating [3,4] and in particular, how these processes interact with homeostatic mechanisms controlling energy balance [1]. In this paper, I will discuss two interpretations of the implications of food reward for healthy eating. Pleasure comes in different disguises: as the immediate sensation of wanting and liking a food when it is eaten or as a longer lasting feeling of well-being after a meal. Berridge and his coworkers have proposed a model of reward based on liking, wanting and learning [2,5]. Liking has been studied very much, despite its inability to predict very much of people's food behaviour [6]. Motivational processes of wanting and desire seem to change more during a meal and to be better able to predict behaviour [7]. Obviously, pleasure derived from a meal also depends on expectations prior to eating it and on bodily and mental satisfactions and well-being experienced after a meal. These are problems that are virtually untouched by scientific investigation. We need to devise new methods of quantifying pleasure and satisfaction. These methods will probably have to rely on measurements of different types of memory and on measurements of interoceptive states [8]. Optimally, the foods we eat should be perceived as ap-petitive, not just as filling. Will high gastronomic quality of foods consumed on a daily basis leads to overeating, thereby exacerbating problems of overweight and obesity? This view has indeed surfaced in certain scientific circles [9-11]. It might, to some, seem almost self-evident, but to others, like myself, not at all so. From highly unscientific introspection and conversations with friends and colleagues about these matters, it seems that most of us eat far less of high-quality Parmesan cheese when it is offered, than of cheap, not so tasty hard cheeses. The same applies to wines and chocolate and all other types of food. Very few people can eat a whole 100 g bar of Valrhona chocolate in one go but easily perform this feat with chocolate of a lesser quality. From a more epidemiological point of view, one would wonder why the obesity problem in France is less severe than in other affluent countries with foods and meals generally of a lower quality than those served in France [12]. Many scientists have argued that