From gut to brain, on the matter of sugar
Liu WW, Bohórquez DV. 2022. The neural basis of sugar preference. Nat Rev Neurosci 23:584–595.
Sweetness is detected on the tongue, but the drive to seek it out originates further downstream, in the gut and in the brain circuits it feeds into. How that signal travels, and where it goes, is the subject of this review.
In the duodenum, neuropod cells detect glucose using sodium-glucose cotransporter 1 (SGLT1) and release glutamate directly onto vagal afferent neurons. This signal travels to the caudal nucleus of the solitary tract in the brainstem, and from there to dopaminergic reward circuits in the basal ganglia and homeostatic feeding circuits in the hypothalamus. Each node in this chain shapes how the brain values and responds to sugar over time.
The review maps the molecular receptors, cell types, neural circuits, and behavioral consequences associated with sugar sensing from the gut surface to the brain. It draws on decades of behavioral work showing that animals can learn to prefer sugar even when taste is bypassed entirely, alongside newer findings that identify the specific cells and transmitters responsible.
The emerging picture is one in which the gut functions as a true sensory organ. One with its own receptors, its own transducers, and its own lines to the brain. Understanding this circuit may explain not just why we crave sugar, but how that craving can go wrong.
