Your brain knows difference between real sugar or artificial sweeteners: Researcher says people’s brains have been wired through evolution to recognize sugar.

Scientists pinpoint the reason why our brains are trained to react to real sugar while artificial sweeteners cut no ice; while stating reasons why it’s possible to gain weight even when switching to “diet” foods.

Sweets have always been the soft spot for most people. A sweet tooth is often used to describe the fondness of sugar. But too much sugar has been linked to health problems such as diabetes and obesity. The advent of artificial sweeteners in diet foods seems to be the perfect answer to satisfy the sweet tooth while losing weight.

But somehow no matter how many low-calorie, fat-free snacks are consumed, we still remain hungry. An explanation for this could lie in the fact that as compared to sugar containing foods, artificial sweeteners lack the calories and energy that our brains have evolved to expect. But just how can organisms tell the difference between artificial sweeteners and real sugar?

Researchers at the University of Michigan have discovered the answer to this question using the common fruit fly, Drosophila melanogaster. In the study, researchers found neurons in the brain of the flies which activated only in presence of real sugar.

Humans share around 75% of the same disease-causing genes with fruit flies, says first author Monica Dus, assistant professor in the Department of Molecular, Cellular and Developmental Biology at U-M.

“The question we tackled was: ‘Do these genes work in the same way in humans to differentiate real sugar from artificial sweetener?’” Dus said in a press release. “It is possible that the genes work the same way in humans. We knew the human brain could differentiate between real sugar and artificial sweeteners, we didn’t how it did so.”

Dus and her colleagues Jason Lai and Greg Suh of New York University School of Medicine first deprived the fruit flies of food for several hours, after which they gave them a choice between real sugar and non-nutritive diet sweeteners. It was observed that when flies licked real sugar, a group of six neurons was activated which caused the release of a hormone.

This hormone had receptors in the brain and gut, which accelerated digestion and allowed the fly to take in more food. But when the fly licked the artificial sweetener, the hormone and digestive reaction was not produced. This can be attributed to the fact that zero-calorie sweetener has no energy or nutritional value.

Dus explains that people’s brains have been wired through evolution to recognize sugar and sweet tasting things signify an energy boost. The brains of fruit flies expect calories when they eat sweet stuff and hence they gravitated towards the real sugar.

The fruit fly has around 100,000 neurons whereas the human brain has 86 billion. The six neurons identified in flies are present in roughly the same area in the human brain. These neurons only fire when they sense real sugar providing a way for the brain to tell the difference between artificial sweeteners and real sugar since the taste of both is the same.

This could explain why diet foods neither satisfy nor satiate humans and why people are prone to gaining weight when dieting. For example, even when you consume an entire package of diet cookies, you will continue to snack on food until you eat something nutritionally significant which fulfills your energy needs.

In previous studies conducted by Dus and her colleagues, it was found that flies, which lacked the ability of taste, still preferred real sugar to artificial sweetener. The scientists also characterized a neural circuit dubbed as Cupcake+ which functions as an on/off switch for eating. When you turn off the Cupcake neurons, it makes the flies stop feeling hungry, Dus said. The study was published in the Journal Neuron.