Obesity is defined as a chronic relapsing disease. It has been associated with shorter life expectancy and both structural and functional brain changes. Bariatric surgery is a procedure to achieve weight reduction and reduce the risk of obesity s comorbidities, with the Roux-en-Y Gastric Bypass (RYGB) being the most used method. RYGB s effects furthermore include hormonal alterations, such as a significant raise in glucagon-like peptide 1 (GLP-1) excretion levels after eating. GLP-1 is excreted by the human digestive system in response to food ingestion and is involved in eating regulation. Resting-state fMRI is a method that measures brain connectivity while the patient is awake and resting. During rest, large scale brain connectivity patterns, or neuronal networks, emerge. Those networks have been related to cognitive functions, and also to body mass index (BMI) and food intake. Effects of bariatric surgery and of GLP-1 before and after surgery on these neuronal networks are poorly studied. As the role of bariatric surgery and GLP-1 on resting-state brain networks related to appetite, satiety and eating behaviors remain underexplored, this study intended to analyze the effects of RYGB surgery on resting-state brain connectivity and to investigate the role of GLP-1 in this process, by blocking GLP-1 receptors. We focused on 6 resting-state networks (ventral attention, default mode, precuneus/hippocampus, right frontoparietal, basal ganglia and insula/anterior cingulate network) that have been shown to be involved in monitoring behavior, were related to food intake and BMI, or include food and reward brain regions. Ten female candidates for RYGB were selected. Participants attended four visits of data collection, two before and two after surgery. All resting-state fMRI scans were performed during the preprandial state, with either placebo or the GLP-1 receptor antagonist Exendin9-39 (used to block effects of endogenous GLP-1) infusion in randomized single-blinded order. Because of an artifact in one of the resting-state fMRI scan, one participant was excluded from the study. We found resting-state functional connectivity decreases in networks that have been implicated in monitoring the external environment, whereas we found increases in functional connectivity in a network that is involved in interoceptive processes. These changes were reversed by post-surgery GLP-1 receptor blockage, suggesting a central role for GLP-1 in post-bariatric surgery brain changes. These findings further suggest a shift in attention to more inward related processes at the expense of external attention. The role of these changes in alterations in feeding behavior and in long-term weight loss have to be determined in future studies.