Glucose is a ubiquitous and essential source of energy for all living organisms. Although mammals have evolved ways to convert other nutritional molecules to ATP, the preference for dietary glucose appears to be preserved. In rodents, the immediate detection of ingested glucose potently reinforces intake, hierarchically organizing behaviors towards glucose-yielding substances, and away from other types of food including other sugars. Taste is the primary sense linked to nutrient selection. Until recently, it was thought that most mammalian species utilize a single broadly tuned receptor to detect all simple sugars. Indeed, this “sweet” receptor, which comprises a heterodimer of the T1R2 and T1R3 proteins, binds multiple natural sugars (e.g., glucose, fructose, sucrose, maltose), as well as various other chemicals that yield little to no energy (e.g., low calorie sweeteners, sugar alcohols) and some d-amino acids. The neural signal originating from the sweet receptor is hardwired into brain circuits that drive eating and drinking behaviors, but it is an unreliable indicator of nutrient quality and quantity.

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