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What artificial sweeteners do to your brain
Artificial sweeteners found in diet sodas and other low-calorie products can make people hungrier, leading them to gain even more weight. Australian researchers think they know why. - photo by Jennifer Graham
Artificial sweeteners found in diet sodas and other low-calorie products can make people feel hungry, leading them to eat more and gain even more weight. That's because they tinker with the brain's reward center, according to a new study out of Australia.

Researchers fed fruit flies a diet sweetened with sucralose (you know it as Splenda) for five days. The insects ate 30 percent more than they did when consuming a diet containing natural sugars. The same thing happened when mice were fed sucralose for a week.

Previous studies have shown that other artificial sweeteners, such as aspartame and saccharine, also cause hunger to spike. The University of Sydney researchers said this is because the brain expects a reward to follow when it perceives something sweet, Tom Philpott reported in Mother Jones. And the brain doesn't take no for an answer.

"They found that inside the brain's reward centers, sweet flavor sensations are accompanied by the expectation of a calorie blast. Since the fake sweetener doesn't deliver the expected calories, the flies go looking for more calorie-rich food to restore balance," Philpott wrote.

In the Australian study, published July 12 in the journal Cell Metabolism, the sucralose diet also made the flies and mice want more natural sugar not because they are gluttons that lack self-control, but because the ancient machinations of their brains are wired to seek nutrients when sensing famine.

In short, artificial sweeteners, with no calories or nutrients, trick the brain into thinking it needs more food.

After sustained consumption of artificial sweetener, the animals could detect much smaller concentrations of real sugar, would eat more of it and respond to it physiologically with much more intensity," lead author Greg Neely told Scientific American.

Another effect was an increase in insomnia and hyperactivity, which stopped when sucralose was removed from the animals' diet.

Of course, a fruit fly does not make a mouse which does not make a human. And Neely told Dr. Bret Stetka, writing for Scientific American, I think the basic message here is that we know the artificial sweetener sucralose is not totally inert at least in animals. This justifies more research into how these compounds affect people as well.

There have been concerns about sugar substitutes since the 1970s, when studies suggested that saccharine caused bladder cancer in rats. Subsequent research, however, found the danger didn't translate to humans, and the Food and Drug Administration, which regulates artificial sweeteners, says they are safe at approved levels. (You can, according to the FDA, have 23 packets of Spenda a day with no ill effect, if you weigh 132 pounds.)

But other studies raise troubling questions about their effect on human metabolism. Earlier this year, Canadian researchers found that expectant mothers who consumed the most sugar substitutes were more likely to have overweight or obese babies. And a 2014 study in Israel concluded that artificial sweeteners can change the composition of some of the trillions of microbes that live in our digestive tracts, the gut flora that influence not only our immune systems, but our brains.

The Center for Science in the Public Interest changed its rating for sucralose from "caution" to "avoid" in February after a controversial study said high doses of Splenda caused leukemia in Swiss rats, a charge that Splenda dismissed as a faulty conclusion of a "poorly conducted and unscientific" report.

Sucralose, according to the Splenda website, is approved for use in 80 countries and is an ingredient in more than 4,000 products worldwide. It was approved by the FDA in 1998.
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