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Drinking Diet Soda and Not Losing Weight? Blame Your Gut Bacteria

We may finally know why artificial sweeteners are linked to weight gain.
Sep 18, 2014· 3 MIN READ
Jason Best is a regular contributor to TakePart who has worked for Gourmet and the Natural Resources Defense Council.

For a while now, scientists have been gathering compelling evidence that the artificial sweeteners found in diet soda and a slew of processed foods sometimes do the exact opposite of what they’re supposed to. Instead of helping us shed pounds, they increase our risk for weight gain and lead to metabolic syndrome, type 2 diabetes, and heart disease. Why?

Turns out, the answer may have been in our gut all along.

In a new study published this week in Nature, researchers at the Weizmann Institute of Science in Rehovot, Israel, have found that a steady diet of artificial sweeteners such as aspartame, sucralose, and saccharin seems to alter gut bacteria in a way that causes blood-sugar levels to rise. That’s the first domino in a chain reaction that can lead to glucose intolerance, weight gain, diabetes, and other related health problems. Not only does the study appear to shed light on the vexing question of why artificial sweeteners might be doing us more harm than good, but it’s part of the next big frontier in medical science: the trillions of bacteria and other minuscule organisms that call our bodies home.

The researchers at Weizmann started with mice. First, they found that mice given water laced with artificial sweeteners developed glucose intolerance. This was not the case for mice given plain old water or (surprisingly) sugar water. It’s part of what has puzzled researchers all along: How can “zero-calorie” sweeteners, which our bodies don’t metabolize into energy or store as fat, cause blood-sugar levels to rise?

The answer, according to the new study, may have to do with proximity. While we don’t digest those sweeteners, they nevertheless come into contact with the legions of bacteria that live in our gut. When researchers used antibiotics to wipe out the gut bacteria of mice, it completely reversed the effects of the artificial sweeteners on the mice’s glucose metabolism. Likewise, when scientists took the gut bacteria from glucose-intolerant mice and transferred it to mice that had had their gut bacteria eradicated, the recipients became glucose intolerant. Analyzing the bacteria more closely, the scientists found “profound changes” in the bacterial populations, “including new microbial functions that are known to infer a propensity for obesity, diabetes, and complications of these problems in both mice and humans.”

The next step was to see whether the same thing happened in humans. Researchers first examined a sample of 381 people, analyzing their blood-sugar levels and colonies of bacteria in their digestive tracts, and found that people who reported consuming higher quantities of artificial sweeteners were more likely to be glucose intolerant. Then they performed a controlled experiment in which a much smaller group (just seven people) who said they did not routinely consume artificial sweeteners were given them for a week. Half began to develop glucose intolerance after just four days, and further analysis showed these participants possessed the kind of gut bacteria that appeared to cause glucose intolerance when exposed to artificial sweeteners.

“Our relationship with our own individual mix of gut bacteria is a huge factor in determining how the food we eat affects us,” said Eran Elinav, one of the study’s lead researchers, in a statement. “Especially intriguing is the link between use of artificial sweeteners—through the bacteria in our guts—to a tendency to develop the very disorders they were designed to prevent; this calls for reassessment of today’s massive, unsupervised consumption of these substances.”

Eran Segal, one of Elinav’s colleagues at Weizmann and a coauthor of the study, was a little more cautious. Because of the small sample size, “by no means are we prepared to make recommendations as to the use and dosage of artificial sweeteners based on the results of this study,” Segal told The Verge.

Another scientist, Christopher Gardner at Stanford University, who was not involved in the research, questioned the study’s design, pointing out that the dose of saccharin given to participants was the maximum amount permitted by the U.S. Food and Drug Administration—the equivalent of a 150-pound person drinking 42 12-ounce sodas per day. “That may be ‘acceptable’ according to some set of guidelines,” Gardner wrote to The Verge in an email, “but it should be noted that realistically this is a very high dose they are using and one that wouldn’t be consumed by a typical consumer.”

Still, as Elinav suggests, the research appears poised to further explain our complicated relationship with the staggering amount of bacteria we carry around with us. The more science emerges focused on our microbiome, what writer Michael Pollan has described as “a vast, largely uncharted interior wilderness that scientists are just beginning to understand,” the more it’s challenging our very notion of who we are.

We are host to an estimated 100 trillion microbial species, only a fraction of which are potentially harmful. That, in effect, means that we’re only about 10 percent human, as Pollan pointed out in The New York Times last year. For every one human cell in our body (those cells containing the DNA we inherited from our parents), there are about 10 microbes. Keeping all those bugs happy—including, perhaps, keeping them away from artificial sweeteners—could help keep our bodies healthy and happy too.