Researchers identified a new system in the brain that senses and integrates the sweetness and energy content of food.

"After chronic exposure to a diet that contained the artificial sweetener sucralose, we saw that animals began eating a lot more," said Greg Neely from University of Sydney.

"Through systematic investigation of this effect, we found that inside the brain's reward centres, sweet sensation is integrated with energy content," said Neely.

"When sweetness versus energy is out of balance for a period of time, the brain recalibrates and increases total calories consumed," he added.

In the study, fruit flies that were exposed to a diet laced with artificial sweetener for prolonged periods (more than five days) were found to consume 30 per cent more calories when they were then given naturally sweetened food.

"When we investigated why animals were eating more even though they had enough calories, we found that chronic consumption of this artificial sweetener actually increases the sweet intensity of real nutritive sugar, and this then increases the animal's overall motivation to eat more food," said Neely.
    
Billions of people worldwide consume artificial sweeteners and they are prescribed as a tool to treat obesity, despite little being known until now about their full impact on the brain and in regulating hunger, researchers said.

They identified a complex neuronal network that responds to artificially sweetened food by telling the animal it has not eaten enough energy.

"Using this response to artificially sweetened diets, we were able to functionally map a new neuronal network that balances food's palatability with energy content," said Neely.
    
"The pathway we discovered is part of a conserved starvation response that actually makes nutritious food taste better when you are starving," he said.

Researchers also found artificial sweeteners promoted hyperactivity, insomnia and decreased sleep quality - behaviours consistent with a mild starvation or fasting state with similar effects on sleep also previously reported in human studies.

To discover whether artificial sweeteners also increased food intake in mammals, researchers replicated the study using mice.

Again the mice that consumed a sucralose-sweetened diet for seven days displayed a significant increase in food consumption, and the neuronal pathway involved was the same as in the fruit flies, researchers said.

"Artificial sweeteners can actually change how animals perceive the sweetness of their food, with a discrepancy between sweetness and energy levels prompting an increase in caloric consumption," said Herbert Herzog from Garvan Institute of Medical Research in Australia.

The findings were published in the journal Cell Metabolism.

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