Podcast Transcript: Brains can register a food’s caloric value independent of our taste buds, say scientists from Duke University and from Portugal. First the scientists engineered mice without taste receptors for sweets. They compared the so-called sweet-blind mice to normal mice. Both were offered plain water or water with sucrose. And within about ten minutes, even the sweet-blind mice preferred the sugar water. The same test was repeated with sucralose, a calorie-free sweetener. The mice that could taste the sweetener preferred, but the mice without the taste receptors never developed a preference for the fake stuff.

Then the researchers looked at the brains of the sweet-blind mice. Sucrose turned on neurons in the brain’s food-reward system. And the brain chemical dopamine was elevated—dopamine is a crucial part of the brain’s reward circuitry. These changes show that the brain’s reward system can detect internal physiological changes even independent of taste—maybe through the digestive system. The work appears in the March 27 issue of the journal Neuron. Scientists are calling this nutrient awareness the brain’s sixth sense for calories. They say teasing out these mechanisms could have implications in understanding and combating obesity.

—Cynthia Graber

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