The diet soda debate rages on: this time, with some intriguing new information.

The journal Nature published a new study that shows that diet sodas may alter your gut microbes in a way that increases the risk of metabolic diseases, such as Type 2 diabetes.

In the paper, researchers at Israel’s Weizmann Institute of Science fed certain zero-calorie sweeteners, including saccharin, aspartame, and sucralose to mice. NPR’s The Salt spoke with researcher Eran Elinav, who said, To our surprise, [the mice] developed glucose intolerance.”

Mice aren’t people, so of course the researchers wanted to see what happened with human subjects. Of 400 people enrolled in an ongoing nutritional study, the researchers found that people who were heavy consumers of artificial sweeteners had slightly elevated HbA1C levels—a long-term measure of blood sugar—as compared to people who consumed little to no artificial sweeteners.

The researchers wanted to take it further, so they had seven people who didn’t regularly drink diet drinks volunteer for their next experiment. For one week, those seven volunteers were instructed to consume an amount of artificial sweetener equal to 10 to 12 single-serving packets.

Four of those seven people developed significant blood glucose issues after just one week—some even shot up to pre-diabetic levels after only a few days’ exposure to artificial sweetener.

Before you go dumping out that case of diet soda you have chilling in the office fridge, The Salt spoke to NYU Human Microbiome Program director Martin Blaser. He cautions that we shouldn’t jump to conclusions, and adds that a lot more research is needed. As The Verge points out, the most important takeaway from this is that not everyone’s microbiome processes artificial sweeteners—or anything else—in the same way.

What appears to happen is that artificial sweeteners, like everything else we eat, affect your individual microbiome. Some bacteria aid in keeping glucose under control, and artificial sweeteners basically change your gut’s microbial makeup. Blaser says that researchers first need to confirm that this is actually happening, and then figure out how it’s happening.

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This isn’t the first time diet soda consumption has been linked to an increased Type 2 diabetes risk. New York Daily News reports that France’s National Institute of Health and Medical Research released a study last year that involved 66,000 female French volunteers, who were monitored over the course of 14 years. That study found a 15 percent higher risk of development of type 2 diabetes for women who drank 16.9 oz. of diet soda per week, compared to the same amount of non-diet soda. The risk increased to 59 percent for women who drank 50 oz. of diet soda per week.

By contrast, women who drank only unsweetened fruit juice and drank no soda at all experienced no increase at all in their risk of developing type 2 diabetes.

[via The Salt, New York Daily News]

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