Brain reward responses shift based on expectations about sweeteners

Elena Mainetto, from Radboud University, Margaret Westwater, from the University of Oxford, and colleagues at the University of Cambridge explored whether they could change how much people enjoy beverages containing sugar or artificial sweeteners by manipulating previous expectations about the drinks. This work is published in JNeurosci. 

The researchers screened 99 healthy adults averaging 24 years of age, selecting those with similar perceptions of sugar and artificial sweeteners. Participants largely reported liking artificial sweeteners as much as they liked sugar, but, notably, the researchers found that they could alter beverage pleasantness by manipulating people's expectations. When participants falsely believed they were drinking a beverage containing artificial sweeteners, they enjoyed sugar-containing drinks less. Conversely, when people falsely expected drinks to contain sugar, this expectation increased their enjoyment of artificial sweeteners, which coincided with increased activation of a brain area related to reward. Says Westwater, "This could mean that this brain area, the dopaminergic midbrain, processes increased nutrients or calories of sweet flavors, which supports rodent work showing that this brain region is important for sugar seeking." 

According to the researchers, this work emphasizes the importance of expectancy in both behavioral and neural correlates to sweetness processing. Westwater elaborates on potential implications for dietary interventions, saying, "If we emphasize that healthier food alternatives are 'nutrient rich,' or have 'minimal added sugars,' this may create more positive expectations than using terms like 'diet' or 'low calories.' This may help people align their food choices with the brain's preference for calories while supporting behavior change." While Westwater acknowledges that this information isn't new in a clinical sense, she hopes that the findings of this study shape how neuroscientific researchers look at diet and eating habits.