By Rita Rubin
WebMD Health News

Reviewed by Hansa D. Bhargava, MD

Sept. 17, 2014 — If you’re one of the millions of Americans for whom diet sodas and artificially sweetened desserts play leading roles in efforts to shed pounds and help prevent long-term diseases like diabetes, new research might give you pause.

The work, done with mice and humans, suggests that artificial sweeteners could raise your blood sugar levels more than if you indulged in sugar-sweetened sodas and desserts.

Blame it on the bugs in your gut, scientists say. They found that saccharin (a.k.a. Sweet’N Low), sucralose (a.k.a. Splenda) and aspartame (a.k.a. NutraSweet and Equal) raised blood sugar levels by dramatically changing the makeup of the gut microorganisms, mainly bacteria, that are in the intestines and help with nutrition and the immune system. There are trillions of them — many times more than the cells of the body — and they account for roughly 4 pounds of your body weight.

Scientists in recent years have focused more and more on the link between the gut microorganisms and health.

In the latest research, “what we are seeing in humans and also in mice is this previously unappreciated correlation between artificial sweetener use” and microorganisms in the gut, said Eran Elinav, MD, one of the scientists involved in the new study. Elinav and a collaborator, Eran Segal, PhD, spoke at a press conference held by Nature, the journal that published their team’s findings. Both of the scientists are on the faculty of the Weizmann Institute of Science in Israel.

“Initially, we were surprised by the results, which is why we also repeated them multiple times,” Segal said.

One industry group said the small number of mice and people studied make the findings hard to apply to larger populations. But one scientist not involved in the research called the small study of humans “profound.”

Study Details

Segal and Elinav added saccharin, sucralose, or aspartame to the drinking water of mice and found that their blood sugar levels were higher than those of mice who drank sugar water — no matter whether the animals were on a normal diet or a high-fat diet.

The mice given artificially sweetened water “were almost diabetic,” said Martin Obin, PhD, who was not involved in the research but read the paper. Obin is an adjunct scientist in the nutrition and genomics laboratory at Tufts University’s Jean Mayer USDA Human Nutrition Research Center on Aging. He said he calculated that the mice fed artificial sweeteners took in a daily amount equivalent to what humans get in about four cans of diet soda.

Although saccharin, sucralose, and aspartame are three different compounds, “the effects were quite similar to each other,” Segal said. Those three sweeteners make up the bulk of the market. Segal said more research is needed to see whether others, such as stevia, can also change the collection of microorganisms in the gut.

When the sweetener-fed mice were given antibiotics to clear their gut of bacteria, their blood sugar levels dropped back down to normal. To gather more evidence of the relationship between artificial sweeteners, gut bacteria, and blood sugar levels, the researchers transferred feces from mice that drank artificially sweetened water into mice that never had. Sure enough, blood sugar levels rose in the recipients.

Of Mice and Humans

The scientists also studied nearly 400 people and found the bacteria in the guts of those who ate and drank artificial sweeteners were different from those who did not. People who used artificial sweeteners also tended to have higher fasting blood sugar levels and a forerunner of type 2 diabetes called impaired blood-sugar tolerance.

Finally, the researchers recruited seven volunteers, five men and two women, who normally didn’t eat or drink products with artificial sweeteners and followed them for a week, tracking their blood sugar levels. The volunteers were given the FDA’s maximum acceptable daily intake of saccharin from day two through day seven. By the end of the week, blood sugar levels had risen in four of the seven people. Transfers of feces from people whose blood sugar rose increased blood sugar in mice, more evidence that the artificial sweetener had changed the gut bacteria.

“It’s small,” Obin said of the seven-person study, “but it’s very, very profound.”

Haley Stevens, PhD, president of the Calorie Control Council, an industry group, said the human as well as the mouse studies were too small to conclude that the findings apply to larger groups.

“In contrast to the assertions made by the researchers of this study, the overall evidence from studies on low-calorie sweeteners shows that these sweeteners are safe and do not have adverse effects on blood glucose control,” Stevens said in a statement.

But previous observational studies about the safety and effectiveness of artificial sweeteners have not unanimously concluded that they’re safe for managing diabetes, Elinav said.

Obin said the new research might provide an explanation for mixed findings in previous studies. As in the people studied, drinking artificial sweeteners did not affect blood sugar levels in all of the mice. That points out differences in the gut bacteria collections from person to person or animal to animal. Besides diet, genetics, health status, and sex all contribute to these differences. “Perhaps not all of the (individual) microbial compositions would indeed be susceptible to the action of the sweeteners,” Segal said.

Questions Remain

Why the sweeteners changed the gut bacteria in some people and mice isn’t known. “This field is still in its infancy,” Obin said. But, he added, “with all the sweeteners that people are taking, this is a major health issue.”

Between 1986 and 2010, the number of American adults eating and drinking sugar-free foods and beverages jumped from 78 million to 187 million, according to the Calorie Control Council. Diet soft drinks are the most popular sugar-free products, followed by non-carbonated soft drinks, gum, and sugar substitutes, according to the organization.

“By no means do we believe that, based on the results of this study, we are prepared to make recommendations on the use and dosage of artificial sweeteners,” Segal said.

Elinav did say, though, that their findings have spurred him to stop using artificial sweeteners in his coffee.

He doesn’t use sugar, either. “I think we must stress that by no means are we saying sugary drinks are healthy,” Elinav said.

SOURCES: Suez, J. Nature, published online, Sept. 17, 2014. Eran Elinav, MD, Weizmann Institute of Science, Rehovoth, Israel. Eran Segal, PhD, Weizmann Institute of Science, Rehovoth, Israel. Martin Obin, PhD, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Medford, MA. Haley Stevens, PhD, president of the Calorie Control Council.

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