Unconscious manipulation of human diet-related behaviors by the internal and external environment

Abstract

<strong>Study I: Manipulated by Marketing and Hormones? The relevance of Oxytocin for Marketing Placebo Effects on Food Product Perception</strong><br /> What consumers expect from food products and how they experience food products strongly depends on product information like premium prices, famous brand names, or organic claims. Many studies demonstrated that these marketing means influence subjective and objective experiences like taste pleasantness and cognitive performance. This phenomenon has been coined marketing placebo effects (MPEs). Still, the neurobiological mechanisms mediating MPEs are unclear. Recent research investigated the neuropeptide oxytocin for its effects on analgesic and cognitive placebo responses. We extend this line of research by testing whether oxytocin boosts marketing induced placebo responses on taste perception and cognitive performance by strengthening the consumer-marketer relationship. We conducted a randomized, double-blind, and pre-registered study with healthy male participants, who either received an oxytocin (24 IU) or sham nasal spray. First, we studied MPEs of price and organic labels on experienced taste pleasantness. Second, in a more exploratory part, we used an energy drink label to study the MPE of brand name and advertisement on cognitive performance. Our results showed no effect of intranasal oxytocin on marketing-induced taste preference. The consumer-marketer relationship, assessed in form of trust and expectations, did also not differ between sham and oxytocin group. Our exploratory analysis suggests a possible role of OXT for MPEs on cognitive performance, which is, however, not supported by a Bayesian analysis. Therefore, this finding needs further confirmation in future research.<br /> <strong>Study II: Manipulated by Gut Bacteria? The Impact of a Synbiotic Intervention on Food Choice Behavior and its Neural Correlates</strong><br /> The gut microbiota influences human health and behavior. One behavior, which directly impinges on health, is eating behavior. Recent research on the Microbiota-Gut-Brain axis suggests a bidirectional relationship between eating behavior and gut microbial composition. Not only does human nutrition affect the microbial composition, the microbial composition also affects diet-related behaviors. Yet the neurobiological mechanisms of how the gut microbiota influences eating behavior are unclear. In a double-blind, placebo-controlled study in healthy male participants, we modulated the gut microbial composition with a 7-week synbiotic intervention. We investigated the effects of this synbiotic intervention on anthropometric data, self-reported eating behavior, and subjective taste- and health-ratings. We further collected behavioral and fMRI data while participants made binary food choices between snack food items of varying taste and health. We found that the synbiotic intervention increased the impact of taste attributes on food choice and led to a significant decrease in choice and health-rating times. An fMRI region of interest analysis did not show any impact of the synbiotic intervention on previously described brain regions that reflect subjective food value and food attributes during choice. Exploratory, uncorrected whole-brain analyses revealed subtle synbiotic intervention effects on various other brain regions. However, these exploratory results require further confirmation. Our data suggests that a synbiotic intervention does not per se influence the ability to eat healthy. Instead, a synbiotic intervention might modulate the responsiveness to individual food attributes and the decision speed when subjectively judging food and deciding for a food product.