Leiden University Student Repository

Charalambides, Sophie Kayo (2026)

The Role of Expectations in Placebo and Nocebo Effects on Hunger: Examining the Influence of Body Mass Index, Body Image, and State Mood on Expectation-Driven Hunger Responses

Master thesis | Psychology (MSc)

With the change in the biological regulation of hunger and its impact on the rising rates of eating disorders and obesity, exploring the cognitive and psychological mechanisms behind this shift has become increasingly important. One recent area of focus is the placebo and nocebo effect, as they have implications for scalable interventions and explain to what extent differences in hunger perception are due to one of the underlying mechanisms: expectations of the treatment. This experimental study investigated the extent to which expectations mediate the placebo and nocebo effects on reported changes in hunger levels. This study then dove deeper into the role of expectations in hunger manipulation by also examining whether individual differences in Body Mass Index, body image, and positive and negative state mood moderate the relationship between expectations and reported hunger levels. This study assigned 126 non-clinical participants to a placebo (hunger suppression), a nocebo ...Show moreWith the change in the biological regulation of hunger and its impact on the rising rates of eating disorders and obesity, exploring the cognitive and psychological mechanisms behind this shift has become increasingly important. One recent area of focus is the placebo and nocebo effect, as they have implications for scalable interventions and explain to what extent differences in hunger perception are due to one of the underlying mechanisms: expectations of the treatment. This experimental study investigated the extent to which expectations mediate the placebo and nocebo effects on reported changes in hunger levels. This study then dove deeper into the role of expectations in hunger manipulation by also examining whether individual differences in Body Mass Index, body image, and positive and negative state mood moderate the relationship between expectations and reported hunger levels. This study assigned 126 non-clinical participants to a placebo (hunger suppression), a nocebo (hunger enhancement), or a control group. The placebo and nocebo effects were induced through sham vagus nerve stimulation and verbal suggestions. As hypothesised for the placebo group, participants’ expectations of hunger mediated the relationship between group assignment and a change in hunger levels. Contrary to our hypothesis, the nocebo effect was not mediated by expectations. Further, only positive state mood significantly strengthened the relationship between expectations of hunger and subsequent reported hunger. BMI, body image, and negative state mood did not significantly moderate the relationship. By examining hunger suppression as a placebo treatment mediated through expectations and hunger enhancement as a nocebo treatment, this study contributes to the growing body of research in this field. Furthermore, by investigating expectations and examining variables as moderators, possible directions for intervention design for hunger-related disorders were provided.Show less

Placebo, Nocebo, Hunger, Body Mass Index, Body Image, Positive State Mood, Negative State Mood

Author

Charalambides, Sophie Kayo

Faculty

Faculty of Social & Behavioural Sciences

Specialisation

Health and Medical

Supervisors

Kaya Peerdeman

ECTS Credits

20

Language

en