<qa>  What is the main outcome of the study?In this study, we would like to explore the hypothesis that changes in metabolic state, induced by altering hormone levels and patterns of neural activity, affect the experience of anxiety in humans. We will also investigate if there is a link between high anxiety and higher caloric intake. Our aim is to characterize whether changes in current metabolic state systematically influence anxiety induced by a well established behavioral task known as the threat of shock. The neural regions activated by this behavioral task in healthy subjects have been well characterized. We have a priori regions of interest that include the insula, anterior cingulate cortex, hypothalamus, amygdala, and prefrontal cortex. As our primary outcome, we will assess neural activation with whole-brain functional magnetic resonance imaging to determine whether brain regions are differentially engaged when subjects experience anxiety across different metabolic states. We will correlate these changes with psychophysiological measures of anxiety and metabolic state. 