Section 0

Introduction

Food is essential for animal life and food-related behaviours are central to ethology. In humans, food means more to us than just catabolism. Food is a source of great pleasure and plays an important social role in our lives. Food psychology has much to study.

Past research has studied many aspects of behaviour relating to food, like the regulation of food intake and the choice of what foods to eat. Yet we also make decisions to reject certain food (or potential food) items and food rejection behaviour is the subject of this thesis. Choices to not eat at all, for example because of satiety, are not covered.

Ingestion is inherently dangerous. In order to allow digestion, an organism exposes itself to many dangers. Food rejection behaviours ward against such dangers. Food rejection is the flip side to food choice, an important part of ensuring the best possible diet is consumed. In humans, food rejection may have other roles. For example, food taboos are a strongly preserved element of many cultural identities.

An understanding of food rejection behaviours is not simply pure science; it has important applications too. Food scares (population wide food rejection behaviours) are of great political significance, particularly in the UK ever since the BSE crisis. 1999 has seen continued concern over genetically-modified foods and the Government and biotechnology companies would do well to consider the psychology literature on this topic (e.g. Frewer, Howard, Hedderley & Shepherd, 1998). May 1999 also saw concerns over the contamination of poultry feed with dioxins having profound political and economic consequences in Belgium and across Europe, followed in June by what appears to be an episode of mass sociogenic illness surrounding a scare about Coca-Cola (Nemery, Fischler, Boogaerts & Lison, 1999).

There are many interventions where knowledge about food rejections could prove useful. There are times when we want people to reject certain items. Medical science now recognises diet as a (possibly the) major determinant of health in the developed world and health educationalists want us to avoid certain foods. Medicines can be dangerous and preparations can be designed to discourage children from accidentally poisoning themselves.

More often, we want people not to reject certain items. There are many foods people may reject that would be valuable additions to a healthy diet. People tend to reject novel foods, a neophobia, and overcoming neophobia is of great importance to food manufacturers with a new product, as the advertising campaign for the drink Dr Pepper demonstrates ("To try it; is to love it").

There are also a range of what we might call food rejection psychopathologies, where food items are rejected through inappropriate behaviours to the detriment of the individual’s well-being. For example, in "cancer anorexia", it appears that a range of food items become aversive after association with nausea produced by the cancer or treatment for the cancer. This thesis concentrates on healthy individuals but is of relevance to some psychological conditions for it is often easier to understand the psychological mechanisms at play when they are working properly than in the pathological case.

Of course, some food rejections have been extensively studied. The literature on anorexia nervosa is immense and eating disorders dominate the lay person’s ideas of food psychology in the author’s experience. Many other issues sport comparable past research efforts across many disciplines, from the anthropology of religious food taboos to the psychology of the perception of bitter tastes. This thesis aims to take an overview of food rejection, to bring together perspectives on different food rejection behaviours.

Are there certain sorts of people who are more prone to reject food items? Can we explain interpersonal differences in food rejection? Section 1 considers one approach to this question, the list heuristic, reviewing its past use, dating back to 1939, and presenting data from two new samples. In the list heuristic, one asks a fixed question about a list of foods, usually whether the subject would reject that food. The number of foods rejected forms a psychometric variable indexing food rejection behaviour.

With this measure of the tendency to reject foods, one can then study interpersonal differences and look for correlations with other variables. Past studies have found a relationship with anxiety, with more anxious people rejecting more foods, and sensation-seeking, with sensation-seekers rejecting fewer foods. These findings are investigated in two rather different sample populations.

While the idea of the list heuristic is very simple, which is perhaps why it has been independently invented at least three times, the details are very much more complicated. Which foods should go on the list? How long should the list be? What should be the question asked about each food? And, most importantly, do changes in the details of the methodology—and past studies have been very varied—affect the underlying phenomenon being measured? Section 1 considers these problems.

Questions about what foods to include in the lists leads to a consideration of the different forms food rejection behaviour can take. The list heuristic is too simple a methodology if we do not understand the variety of behaviours under study. The common absence of consumption in food rejection phenomena hides a wide variety of behaviours. Section 2 considers the multifaceted nature of food rejection behaviours and, as a corollary to that, the need for a taxonomy of human food rejections.

Rozin & Fallon (1980; Fallon & Rozin, 1983) asked subjects a suite of questions for each of many food rejections. These questions considered different aspects of food rejection. For example, we can distinguish between a negative hedonic response, when we do not like the taste of something, and a feeling of nausea in response to an item. A food item may be palatable, yet we may wish to avoid it as we fear negative post-ingestive consequences; the food could be poisonous or otherwise detrimental to our health. With responses across a range of questions, various statistical techniques allow one to construct a taxonomy from the responses. Having recognised the diversity of food rejections, we want to tame that diversity. By discovering a structure, we can take experiences of one food rejection and relate it to a similar food rejection. The methodology and statistical techniques of Rozin & Fallon (1980; Fallon & Rozin, 1983) are developed to allow a replication of and development from their studies.

Section 3 of this thesis considers learned food aversions (LFAs). Nausea after eating a food can lead to an aversion to that food, particularly if the food was novel. LFAs are perhaps the most studied of all food rejection phenomena, but work has principally been in rodents. Research in humans is sparse, yet there are important clinical implications in humans to work on LFAs as they may be related to problems like ‘cancer anorexia’ and anticipatory nausea and vomiting (ANV) in patients undergoing treatment regimes that produce chronic nausea.

Section 3 serves to illustrate the utility of the ideas introduced in Section 2. Although LFAs have been extensively studied previously, a recognition of the multi-faceted nature of food rejection behaviour brings a valuable perspective as understanding the nature of the aversion is important to understanding possible clinical implications. I posit that a LFA produces a learned nausea response to the target food and this hypothesis is tested in two studies on human volunteers.