Flies given the artificial sweetener sucralose get hooked on the taste, eating more sugar and negating any calorie reduction they might experience from using the artificial sweetener in the first place. The researchers of the paper in Cell Metabolism are wary of extrapolating to humans, but advocate at least knowing how much artificial sweeteners are in one's diet.
Artificial sweeteners have become a huge industry. However, according to senior author Dr Greg Neely of the University of Sydney, there is conflicting evidence as to whether they replace sugar consumption, or stimulate more demand. That's not all that surprising. Nutritional studies on humans are notoriously hard, because so many people don't stick to the diet and don't admit it to researchers when they stray. Tightly controlled nutritional research tends to be on very small groups, for short periods of time, or both.
Animal diets are much easier to control. Neely told IFLScience that fruit flies are particularly good to work with because it is possible to test a lot of diets quickly.
“We then applied one component to mice,” Neely said. “We couldn't do the whole thing in mice because it would take years.” Confirming that, at sufficient doses, sucralose triggers a similar craving in mammals gave Neely's team more confidence of its wider application.
"After chronic exposure to a diet that contained the artificial sweetener sucralose, we saw that animals began eating a lot more," said Neely in a statement. "Through systematic investigation of this effect, we found that inside the brain's reward centers, sweet sensation is integrated with energy content. When sweetness versus energy is out of balance for a period of time, the brain recalibrates and increases total calories consumed."
He added: "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. The pathway we discovered is part of a conserved starvation response that actually makes nutritious food taste better when you are starving,"
Neely cautioned that the work may not be applicable to all artificial sweeteners. “Fruit flies don't like saccharine,” he told IFLScience, while aspartame proved difficult to administer. Nevertheless, the same mechanism could easily apply to anything that tastes sweet.
When the fruit flies were given sucralose for more than five days, their energy intake increased by up to 30 percent, with Neely telling IFLScience that the more sweetener they were given, the more they ate.
The implications for our own diets are less clear. Neely told IFLScience that to a human, sucralose is 600 times as sweet as sucrose, gram for gram, while flies only find it four times as sweet. So the flies were consuming quantities, relative to body weight, no human would touch. Rather than suggesting dieters should cut artificial sweeteners out entirely, Neely suggested clearer labeling might be beneficial so that people know how much they are consuming.