Abstract
The modern food environment, providing easy access to an abundant supply, is thought to be one of the key contributors to the current obesity epidemic (e.g., Chaput, Klingenberg, Astrup, & Sjödin, 2011; Ferretti, Mariani, & Sarti, 2021). However, why some individuals are more susceptible to the current obesogenic eating environment than others represent a key research question. Over recent decades, research has gathered evidence for sensory effects on eating behaviour and body adiposity. For instance, individuals with obesity show declined sensitivities in olfactory and auditory senses. While this evidence points to a promising research direction, it remains perplexing how an individual’s sensory function affects their food-related behaviour. Recent behavioural and neurological research has highlighted the importance of cross-modal interactions across the five senses, which has led to an intriguing research direction to investigate combined sensory effects on eating behaviour. Understanding individual differences in susceptibility to pleasurable food and body adiposity might rest into testing for individual multi-sensory abilities – the multi-sensory fingerprint.
In the first part of the thesis, 98 healthy Caucasian males (M±SD: Age=25.9±5.7; BMI=26.8±5.1) were tested for sensory discriminability (measured by d′) to three olfactory, three gustatory, three visual and two auditory food-related stimuli. This cohort of participants was also assessed for their food-related psychological and physiological profiles, including personality traits, anxiety/depression levels, positive/negative affect, eating style, body mass index (BMI), body fat percentage (BFP), and hormonal measures of peripheral ghrelin, insulin, and leptin levels. A sub-group of this cohort (N=37) also participated in a food reward EEG study. The latter study investigated the frontal cortical responses to food versus money reward, initiated by a probabilistic reward task (PRT). Additionally, this experiment also included a Food Go/No-Go task, which assessed participants’ impulsivity towards food.
In this thesis, the establishment of a multi-sensory fingerprint was firstly discussed. Sensory discriminability results revealed a stark contrast in the multi-sensory fingerprints, with three distinct patterns - i.e., enhanced multi-sensory discriminability (Cluster 1), reduced multi-sensory discriminability (Cluster 2) and reduced chemosensory discriminability coupled with enhanced visual and auditory discriminability (Cluster 3). Further assessments of individuals in these three multi-sensory clusters suggested significant differences in terms of BMI (p = 0.010), anxiety level (p = 0.017), and eating style (p = 0.003), but no difference in personality traits, positive/negative affect or peripheral ghrelin, leptin, and insulin were observed. Specifically, Cluster 3 was characterised by a relatively high BMI (mean ± SD: 28.04 ± 5.11) and Cluster 1 a rather low one (mean ± SD: 24.68 ± 2.74), while Cluster 2 demonstrated high anxiety levels and restrictive eating behaviour. Finally, results from the last chapter revealed that Cluster 2 and 3 showed preferential bias towards food over monetary rewards. Additionally, these results have indicated a frontal asymmetry in response to money and food reward, with a left-lateralised activity associated with food reward and a right-lateralised activity with money reward. Such frontal asymmetry appeared to be notably stronger in response to food for the higher BMI groups with a specific multi-sensory fingerprint (Cluster 3).
Altogether, this thesis is the first to test for individual multi-sensory discriminability and relate it to food-related physiological and behavioural responses. With data from a wide range of measures, this thesis provides novel and important insights into inter-individual differences associated with multi-sensory sensitivities. These fundamental findings offer a better understanding of obesity and provide new opportunities for the management of this metabolic pathology.