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The debate over whether diet sodas are good or bad for us never seems to end. Some research suggests zero-calorie drinks to help people cut calories and fend off weight gain. But in recent years, the idea that artificial sweeteners may prompt people to eat more or even raise the risk of metabolic problems has gained traction, too. Well now, as NPR's Allison Aubrey reports, a study published in the journal "Nature Today" adds another wrinkle to the debate. It seems gut microbes may play a role in determining whether diet drinks agree with us or not.
ALLISON AUBREY, BYLINE: When diet soda was introduced decades ago, one aim was to help people with diabetes. Unlike sugary drinks which can lead to spikes in blood sugar, the belief was that the artificial sweeteners - such as saccharin and aspartame - would help keep blood sugar levels stable. But new science suggests that the sweeteners have a much more complicated and unpredictable effect on our bodies.
ERAN ELINAV: The evidence for their beneficial effect is really controversial.
AUBREY: That's Eran Elinav, a researcher at the Weizmann Institute of Science in Israel. A few years back, he began an experiment feeding mice water sweetened with either real sugar or with artificial sweeteners. The thinking was that the real sugar might induce metabolic problems. But it turns out the artificial sweeteners raised blood sugar the most.
ELINAV: To our surprise, they developed glucose intolerance as compared to mice that consumed sugary water.
AUBREY: Elinav and his colleagues were intrigued by this, and they set out to determine if it might be true in people, too. They recruited a small group - seven people who'd never been in the habit of drinking diet drinks and asked them to start consuming a lot of artificial sweetener - the equivalent of 10 to 12 of those little packets per day.
ELINAV: And what we could find is that a subgroup of these individuals - four out of the seven - developed significant disturbances in their blood glucose even after short-term exposure to artificial sweeteners.
AUBREY: The blood sugar of some went from being normal up temporarily to levels that are characterized as pre-diabetes. And this happened within five days.
ELINAV: Yeah, this was a surprise to us.
AUBREY: And how it may be happening is even more surprising. Their experiments show that artificial sweeteners can alter the mix of bacteria in the guts of mice and people in a way that can lead some to become glucose intolerant.
MARTIN BLASER: I found this work exciting because to me it's a new idea.
AUBREY: That's physician Martin Blaser who directs the Human Microbiome Program at New York University.
BLASER: I can just tell you that having read the paper yesterday, and as a middle-aged man who is concerned about his diet and his waistline, and as somebody who drinks diet soda, I didn't drink any yesterday. (Laughter).
AUBREY: Blaser says while this paper is preliminary, it could begin to explain why studies of diet soda point in opposite directions.
BLASER: All of us have a microbiome. The microbiome is extremely complex. Everybody's microbiome is a little different.
AUBREY: And may respond differently to the foods and artificial compounds we eat. For some people, it could be that artificial sweeteners lead to changes in the gut microbiome the crowd out bacteria that were helping keep glucose in check. Or, Blaser says, the other possibility is that the sweeteners lead to the proliferation of bacteria that elevate glucose levels.
BLASER: It could be in either direction or a combination. We don't know.
AUBREY: And Blaser says a lot more research is needed. After all, there were just seven people in the experiment.
BLASER: So that's the next step in this war is to - firstly, for somebody to confirm this to see is it really true? And secondly, is to extend the work to understand the mechanism. How does the change in the microbial composition - how is it causing this?
AUBREY: Until then, Blaser says he might just continue to give diet soda a break. Allison Aubrey, NPR News.
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