Are food odours special? A systematic review of food odours as experimental stimuli to study reward responses in human subjects

Background: Food odours are often used to study anticipatory food reward, yet it remains unclear whether they evoke stronger reward responses than other odours or food cues presented in other sensory modalities. We systematically reviewed the literature to evaluate these assumptions.Methods: MEDLINE, Embase and Web of Science were searched. Experimental studies investigating behavioural reward responses to orthonasal food odours in healthy participants were included. Two primary contrasts were considered: (1) food vs. non-food odours and (2) food odours vs. food stimuli, as well as the influence of hunger and satiety. Risk of bias was assessed using QualSyst and certainty of evidence using GRADE. A co-occurrence network of odours used in the field was constructed. Results: Of the 64 included studies, 11 compared food with non-food odours (total N = 363) statistically, while three compared food odours with pictures (total N = 216). Evidence for greater reward responses to food than non-food odours was limited and inconsistent, although positive findings tended to originate from larger studies. Evidence suggesting that food pictures elicit stronger reward responses than food odours was limited due to the small evidence base and methodological heterogeneity. Across studies, odour selection was concentrated on a small number of stimuli.Conclusions: Few studies have directly examined assumptions underlying the use of food odours as reward stimuli. Greater methodological standardisation and explicit stimulus comparisons are needed to establish under which experimental conditions food odours provide an optimal model of anticipatory food reward. This work was funded by the ERC (grant agreement No. 947886) and registered at OSF.IO/237FW.Keywords: odour, vision, food reward, hunger, satiety, network