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New Research Uncovers the Neuroscience of Sugar Fiending

The brain doesn't want sugar, it wants energy. Even if it tastes disgusting.

The most fundamental unit of nutrition is the calorie. Stop consuming foods with significant calorie content, and you will most certainly die. You would die well before you would die as the result of cutting out any more specific or proper nutrient or nutrient category, such as fats, carbohydrates, vitamins, or proteins. These things are obviously all important, but to have a living body worth nourishing means providing that body with basic energy. You can't live off vitamins alone.

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Fortunately, the stuff we call "food" usually comes loaded with both calories and vitamins and other things we more typically think of as nutrients. We don't have to worry much about not getting enough calories given how calorie-dense our food supply is, generally, in the first-world.

But the brain still clings to this most fundamental of needs. Research published this week in Nature Neuroscience from neuroscientists at Yale University shows how the brain is able to effectively count calories by way of a separate neural circuit driving us to select energy-dense foods. Crucially, this turns out to be a separate circuit from the one that drives us to select sweet foods; in other words, given a choice between sweetness and calories, our brains really want us to go after the calories.

The neurological distinction is thus between nutritional impulses and "hedonic" impulses, e.g. between bare calorie content and pleasure/tasting good. These two things are even processed in separate regions or strata (dorsal and ventral, back and front) of the brain, according to the Yale group.

Your brain is well-equipped to trick you into eating something way gross if it had to for survival's sake.

"During sugar intake, suppressing hedonic value inhibited dopamine release in ventral, but not dorsal, striatum, whereas suppressing nutritional value inhibited dopamine release in dorsal, but not ventral, striatum," the neuroscientists write. "Notably, the activation of dorsal pathways was sufficient to override inhibitory signals generated by ventral pathways during the ingestion of aversive substances. Such circuit logic implemented in the striatum allows the organism to prioritize energy seeking over sensory quality."

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In other words, your brain is well-equipped to trick you into eating something way gross if it had to for survival's sake. Deep down, it wants dopamine, not candy.

The Yale group tested this out using mice using an actual instrument called a "lickometer." The rodents were offered calorie-free sucralose (with various controls in place to ensure that it tasted just like normal sugar, from a mouse's perspective) and, as they licked the sample, infusions of either sugar or sucralose were administered straight to their stomachs. The researchers then kept track of which intra-gastric infusion prompted the most enthusiastic licking (as the mice thought the sugar was coming from what they were licking and not directly from a tube).

"We observed increased dopamine release above baseline levels in [ventral side] during sweetener intake, irrespective of which solution was administered intra-gastrically," the Yale group reports. "However, dopamine release in [dorsal side] increased above baseline levels only when sweetener intake was accompanied by intra-gastric infusions of glucose."

The researchers were also able to get the mice to lick gross-tasting (bitter) solutions by administering direct glucose infusions. As expected, the gross sugar failed to increase dopamine levels in the ventral side (sweet) circuits, but again boosted the levels in the dorsal side (energy) circuits. Energy content had little to do with sweetness-related neural reward activity.

What does it all mean? Well, for one thing, the brain remains completely amazing at keeping you alive, but the research may also eventually have implications in public health. That is, the more we know about what the brain wants neurologically, the better we can help guide people to eat better, e.g. not shove loads of sugar into their systems at every opportunity.