A new study , published in Cell Metabolism , has found when a patient undergoes gastrointenstinal bypass surgery — a weight loss (bariatric) surgery that reduces stomach size in morbidly obese or diabetic patients — it reduces the release of the neurotransmitter dopamine in the brain’s reward and pleasure centers, which in turn reduce their need for sugary foods.

"The problem of how and why bariatric surgery works has been perplexing scientists for years," said senior study author Ivan de Araujo, of Yale University School of Medicine, in a press release. "By shedding light on how bariatric surgeries affect brain function, our study could pave the way for the development of novel, less-invasive interventions, such as drugs that reduce sugar cravings by preventing sugar absorption or metabolism upon arrival in the gastrointestinal tract."

It’s well known that dopamine spikes in people’s brains when they eat sugary foods. This in turn influences how much they eat by encouraging them to continue seeking that reward. Knowing this, the researchers set out to discover if gastrointestinal surgery (also known as gastric bypass surgery) had any effect on that same brain circuitry. To do this, they conducted the same kind of bypass procedure as Roux-en-Y intervention surgery, which involves creating a pathway that passes over the small intestine so the stomach becomes attached to the lower part of the gastrointestinal tract. Breaking away from the procedure, however, they did not attach a gastric pouch to the mice — which would normally limit how much food they ate.

This procedure, called a duodenal-jejunal bypass, was found to minimize the mice’s sugar cravings by inhibiting the release of dopamine. While the researchers aren't exactly sure why this happened, it's possible the bypass prevented the sugar from being absorbed into the small intestine, and therefore it had no effect on the body. Normally, the lab mice would lick a spout that releases a sugary liquid, even when they were full of sugar already — a result of the addictiveness of sugar, which manipulates the dorsal striatum, a part of the brain responsible for decision making.

To prove that what they had found actually worked, the researchers used optogenetics — manipulating DNA in neurons so they fire when light’s shined on them — to activate the dopamine-releasing neural circuit. This led to a reversal of the surgery’s effects; while the mice had no interest in sugar when they was sated, they suddenly became intent on licking the spout when the light was shone on their dopamine-releasing neural circuits.

Weight-loss surgery has been shown to reduce appetite but de Araujo says we still don’t know “ how and why bariatric surgery works.” However, these types of surgeries find success when patients reduce the amount of calories they eat and, seeing as sugar is a good source of calories, discovering a method to turn off our sugar craving mind goes a long way to “help patients lose weight and reverse their diabetes without going under the knife," de Araujo said.

Source: de Araujo, I, et al. Striatal Dopamine Links Gastrointestinal Rerouting to Altered Sweet Appetite. Cell Metabolism . 2015.