Body wisdom: An individual differences approach to advance theory, methods, and interventions of internally regulated eating

Food intake regulation has become a difficult task nowadays. Yet, even under these circumstances, some individuals manage to regulate their eating effectively as they achieve to eat healthily and in moderation. This thesis argues that one effective approach to eating regulation is internally regulated eating. Previous research has shown that this eating style is not only associated with improved health outcomes but also leads to them. However, the literature on internally regulated eating is highly fragmented and built upon limited theoretical accounts.

This thesis embraces the multiformity in this field and uses it to build an integrated theoretical framework of internally regulated eating style, which is used as a basis to advance measurement and applications in this field. The following research questions are addressed in the chapters of this thesis: 1. Which are the individual-difference characteristics that underpin the internally regulated eating style, how do they associate with each other, and how do they lead to effective regulation of food intake?; 2. How can we quantify these individual-difference characteristics in the population?; 3. To what extent does sensitivity to bodily signals of hunger and satiation (trait) manifest itself in behavioural tasks (state)?; 4. To what extent is perception of bodily signals of hunger and satiation (state) affected by focused attention to the body?

To address the first research question, a narrative review of the literature on various paradigms of internally regulated eating was conducted (Chapter 2). Internally regulated eating style was defined as the general tendency to eat in response to physiological signals of hunger and satiation, which is underpinned by a specific set of individual-difference characteristics, namely, 1. sensitivity to physiological signals of hunger and satiation, 2. self-efficacy in using physiological signals of hunger and satiation to determine when and how much to eat, 3. trust on the body’s physiological processes for the regulation of eating (internal trust), 4. a relaxed relationship with food (food legalising), and 5. a tendency to savour the food while eating (food enjoyment). Furthermore, a classical theoretical model of eating behaviour, the boundary model of eating, was used to explain how the internally regulated eating style leads to effective regulation of food intake.

Since none of the available self-report measures could adequately capture the full complexity and theoretical structure of the internally regulated eating style, a new measure was developed (Chapter 3). A stepwise, theory-based, and empirically driven process was used to develop the Multidimensional Internally Regulated Eating Scale (MIRES) and to provide initial evidence for its validity. The scale’s psychometric properties were tested and confirmed in broad samples of consumers from the UK and US. Specifically, evidence on the scale’s internal structure and consistency, measurement invariance, and two-week temporal stability was obtained. In addition, the construct, discriminant, convergent, criterion, and incremental validity of the scale were upheld in this cross-sectional research.

Chapter 4 discussed two pre-registered behavioural experiments that were conducted to assess the construct validity of two MIRES subscales: sensitivity to bodily signals of satiation (SS) and sensitivity to bodily signals of hunger (SH). Associations of SS and SH with behavioural indicators of the incidental ability to perceive the onset of satiation and hunger (respectively) were examined. The water load test was used to assess satiation threshold in the laboratory and the preload test was used to assess hunger threshold in a semi-controlled setting. In addition, participants filled in a self-report measure that taps into the broader domain of awareness of bodily sensations (Multidimensional Assessment of Interoceptive Awareness - MAIA). It was found that in a healthy sample of males and females (19-68 years), SS was not associated with satiation threshold (Study 1). Likewise, in a healthy sample of young females (18-27 years), SH was not associated with hunger threshold (Study 2). MAIA was not associated with the satiation and hunger thresholds either, but it was positively associated with SS and SH. While this research failed to obtain strong evidence on the construct validity of the MIRES subscales, the finding that these subscales tap into the broader theoretical construct they are intended to measure (i.e., interoceptive awareness) provides preliminary support for their construct validity.

Finally, the effect of a brief mindfulness intervention (i.e., focussed attention to the body) on perception of bodily signals of satiation and hunger was investigated in this thesis (Chapter 5). Mindfulness is an increasingly studied concept in the domain of eating regulation and several studies have documented its positive effects on food intake and weight. Yet, little is known about the underlying mechanisms by which mindfulness exerts these effects. This thesis examined one such potential mechanism that has not received adequate attention in prior research. By adding a second experimental group (i.e., mindfulness group) to each of the studies presented in Chapter 4, the studies were turned into quasi experiments, allowing thus, the effects of mindfulness on perception of bodily signals of satiation and hunger to be studied in a controlled experimental setting. A brief mindfulness exercise (body scan) did not influence the perception of satiation (Study 1) but improved the ability to perceive bodily signals of hunger (Study 2). After consuming a standardized preload, participants in the mindfulness group perceived the onset of hunger 18min earlier than those in the control group and this effect persisted also in the presence of control variables. It was concluded that even a single mindfulness exercise can improve the perception of hunger signals substantially, while more intensive mindfulness training may be required to impact the perception of satiation signals.

Overall, this thesis provides a solid theoretical foundation for the study of internally regulated eating style, a reliable instrument that can be used for its measurement, as well as inspiration for potential applications in research and practice in this field. It provides a starting point for a unified understanding of existing non-dieting approaches to eating, supplements (with cross-sectional data) existing evidence on the adaptive nature of the internally regulated eating style, and generates insights that are relevant to various streams of literature, including those on measurement, construct validation, mindfulness, and interoception.