The impact of dietary claims on behaviour: Expectations qualify how actual satiety affects cognitive performance.

Dietary choices significantly impact health and daily cognitive performance, prompting various recommendations for eating habits. Whereas much research has focused on the effects of actual satiety on cognitive performance, the influence of expectations regarding effects of satiety on performance remains underexplored. This study aims to address this gap by examining how the expectation of satiety influences cognitive outcomes, building on existing findings that highlight the role of placebo effects in shaping eating behaviour. This study manipulated participants' expectations of how their satiety (satiated versus hungry) affects their concentration through verbal placebo suggestions and measured effects on their cognitive performance. The sample consisted of four groups who were either satiated or hungry and either read the suggestion that their satiety state enhances or deteriorates their concentration. The suggestion was formulated as a scientific finding. Cognitive performance was measured remotely using a Simon Task. Results showed that if participants' actual satiety state was paired with a positive expectation regarding the state they were in, their performance was better than if it was paired with a negative expectation regarding their current satiety state. So, actual satiety state was not the main driver of cognitive performance, but what participants were led to believe about their current satiety state was. These findings suggest that instructions in intervention studies should be phrased carefully to avoid expectation-related confounds. Additionally, verbal placebo suggestions could be a promising method to enhance cognitive performance in daily life.