Mapping the 'Sweet Brain' in Healthy Participants

Overview

The human brain has a central role in regulating appetite and food intake. It integrates many metabolic, hedonic and trait-related signals that affect eating behaviour and determine when and how much we eat. The effects of non-nutritive sweeteners (NNS) that provide sweet taste with no calories on appetite, food intake thus weight status remain a subject of debate. In this study, the investigators aim to investigate whole brain response to the ingestion of beverages sweetened with caloric sugars (glucose, maltodextrin) or NNS (stevia) as well as neural substrates of attentional bias to food (pre-and post consumption) in healthy lean participants.

Non-nutritive sweeteners (NNS) are zero or no calorie alternatives to caloric sugars and their role in appetite and weight status remains inconclusive. NNS similarly as caloric sweeteners activate the oral sweetness receptors and conscious perception of sweetness. However caloric sugars and NNS differ in their metabolic fate after ingestion, so that caloric sugars lead to raised blood glucose, insulin and satiety inducing gut-peptide levels after meals, but NNS do not influence postprandial metabolism. A recently proposed model suggests that metabolic signals may have indirect effects on food reward processing via alterations in higher cognitive function such as attention (Higgs et al. 2017), the role of sweetness in this model is yet to be examined. In the proposed study stevia-sweetened beverage will be used as the NNS, glucose-sweetened beverage as the caloric sweetener, water as a non-sweet non-caloric control and maltodextrin as a non-sweet caloric control. The study has two aims: first to investigate whole brain responses following the oral consumption of caloric sugars versus NNS using and physiological MRI, and second to examine the neural correlates of the attentional bias to food cues following the consumption of caloric sugars- vs. NNS-sweetened beverages using task-based functional Magnetic Resonance Imaging (fMRI). In this study participants will be asked to come to the imaging facility on four separate occasions, corresponding to the four study beverages, glucose, stevia, maltodextrin and water. Before coming to an imaging session participants should consume a breakfast of their preference at home (which will be repeated before each session) and then fast for 3-4 hours. Upon arrival subjects will fill in their mood ratings, and the breakfast composition questionnaire and will be ready to start. Firstly, neural responses will be measured (before consumption of the study beverages) while subjects perform a food visual dot probe task (VPT) previously validated to show differences in attentional bias to food between fasted and fed states (Stamataki et al. 2019). Secondly, a physiological MRI measurement will be performed (Little et al. 2013) which will last 40 minutes. Third, subjects will perform again the VPT (after the consumption of the study beverage) whilst an fMRI measurement will be performed.