<p>Interoception broadly refers to awareness of one’s internal milieu. Although the importance of the body-to-brain communication that underlies interoception is implicit, the vagal afferent signalling and corresponding brain circuits that shape perception of the viscera are not entirely clear. Here, we use mice to parse neural circuits subserving interoception of the heart and gut. We determine that vagal sensory neurons expressing the oxytocin receptor (<i>Oxtr</i>), referred to as NG^Oxtr, send projections to cardiovascular or gastrointestinal tissues and exhibit molecular and structural features indicative of mechanosensation. Chemogenetic excitation of NG^Oxtr decreases food and water consumption, and remarkably, produces a torpor-like phenotype characterized by reductions in cardiac output, body temperature and energy expenditure. Chemogenetic excitation of NG^Oxtr also creates patterns of brain activity associated with augmented hypothalamic–pituitary–adrenal axis activity and behavioural indices of vigilance. Recurrent excitation of NG^Oxtr suppresses food intake and lowers body mass, indicating that mechanosensation of the heart and gut can exert enduring effects on energy balance. These findings suggest that the sensation of vascular stretch and gastrointestinal distention may have profound effects on whole-body metabolism and, possibly, mental health.</p>