Artificial sweeteners may disrupt the body’s ability to regulate blood sugar, causing metabolic changes that can be a precursor to diabetes, researchers reported.
That is “the very same condition that we often aim to prevent” by consuming sweeteners instead of sugar, Dr. Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, said at a news conference to discuss the findings.
The scientists performed a multitude of experiments, mostly on mice, to back their assertion that the sweeteners alter the microbiome, the population of bacteria that is in the digestive system.
The different mix of microbes, the researchers contend, changes the metabolism of glucose, causing levels to rise higher after eating and to decline more slowly than they otherwise would.
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The findings by Elinav and his collaborators in Israel, including Eran Segal, a professor of computer science and applied mathematics at Weizmann, were published Wednesday in the journal Nature.
Cathryn Nagler, a professor of pathology at the University of Chicago who was not involved with the research but who wrote an accompanying commentary in Nature, called the results “very compelling.”
She noted that many conditions, including obesity and diabetes, had been linked to changes in the microbiome.
“What the study suggests,” she said, “is we should step back and reassess our extensive use of artificial sweeteners.”
Artificial sweeteners are not digested by the human body, which is why they have no calories.
However, they still must pass through our gastrointestinal tract, where they encounter the vast ecosystem of bacteria that thrive in our guts. These bacteria, though not technically part of our bodies, still play an important role in our physiology, including how we process glucose and other sugars.
Previous studies on the health effects of artificial sweeteners have yielded conflicting and confusing findings. Some found that the sweeteners were associated with weight loss; others found the opposite, that people who drank diet soda weighed more.
Some found a correlation between artificial sweeteners and diabetes, but those findings were not convincing because those who choose the products may already be overweight and prone to the disease.
While acknowledging that it is too early for broad or definitive conclusions, Elinav said he has stopped putting artificial sweeteners in his coffee.
Elinav also said, “I think we must stress, by no means are we saying that sugary drinks are healthy.”
In the initial set of experiments, the scientists added saccharin (the sweetener in the pink packets of Sweet’N Low), sucralose (the yellow packets of Splenda) or aspartame (the blue packets of Equal) to the drinking water of 10-week-old mice.
Other mice drank plain water or water supplemented with either glucose or ordinary table sugar. After a week, there was little change in the mice who drank water or sugar water, but the group consuming artificial sweeteners developed marked intolerance to glucose.
Glucose intolerance, in which the body is less able to cope with large amounts of sugar, can lead to more serious illnesses such as metabolic syndrome and type 2 diabetes. When the researchers treated the mice with antibiotics, killing much of the bacteria in the digestive system, the glucose intolerance went away.
The scientists cannot explain how the sweeteners affect the bacteria or why the three molecules of saccharin, aspartame and sucralose result in similar changes in the glucose metabolism.
To further test their hypothesis that the change in glucose metabolism was caused by a change in bacteria, they performed another series of experiments, this time focusing just on saccharin.
They took intestinal bacteria from mice who had drunk saccharin-laced water and injected them in mice that had never been exposed to saccharin. Those mice developed the same glucose intolerance. And DNA sequencing showed that saccharin had markedly changed the variety of bacteria in the guts of the mice that consumed it.
Next, researchers turned to a study they were conducting to track the effects of nutrition and gut bacteria on people’s long-term health.
Among 381 nondiabetic participants in the study, the researchers found a correlation between the reported use of any kind of artificial sweeteners and signs of glucose intolerance. In addition, the gut bacteria of those who used artificial sweeteners were different from those who did not.
Finally, they recruited seven volunteers who normally did not use artificial sweeteners and over six days gave them the maximum amount of saccharin recommended by the U.S. Food and Drug Administration. In four of the seven, blood-sugar levels were disrupted in the same way as in mice.
The researchers also injected the human participants’ bacteria into the intestines of mice, and the animals developed glucose intolerance.
“That experiment is compelling to me,” Nagler said.
Dr. Frank Hu, a professor of nutrition and immunology at the Harvard School of Public Health who did not take part in the study, called it interesting but far from conclusive and added that given the number of participants, “I think the validity of the human study is questionable.”
The researchers said future research would examine aspartame and sucralose in detail as well as other alternative sweeteners such as stevia.
Material from the Los Angeles Times is included in this report.