Diet drinks may have zero calories but those artificial sweeteners are not necessarily sliding through your digestive system unnoticed. According to new research, sugar substitutes can change the guest list at that bacterial party in your intestines known as your microbiota. The researchers who made the finding say that in mice, at least, this disturbance in the internal ecosystem actually raised blood sugar, thus defeating the purpose of these products by increasing risk for type 2 diabetes and obesity.
The findings, released today in the Journal Nature, add to a growing understanding that our internal communities of symbiotic bacteria have a profound influence on metabolism and immunity. “It’s a neglected organ,” said the lead researcher on the paper, Eran Elinav, an immunologist with the Weizmann Institute of Science in Israel. He said he thinks of the human microbiota as a complex ecosystem with thousands of species and sub-species. While bacterial cells are small, they far outnumber those cells we think of as ours.
The new results may finally offer an explanation for previous observations and studies showing that people who used a lot of artificial sweeteners don’t always lose weight. But understanding cause and effect is complicated by the fact that being overweight or at risk of diabetes may cause people to choose artificial sweeteners, rather than the sweeteners causing people to gain weight and develop elevated blood sugar.
This new research included a handful of experiments on mice and people. One striking observation, said Elinav, was that after 11 weeks, mice given artificial sweeteners in solution ended up the same weight as mice given a sugar solution, even though they consumed fewer calories, and the ones on the artificial stuff had higher blood sugar than the sugar consumers. This happened with all three products tested – saccharine, aspartame and sucralose.
Antibiotics reversed the high blood sugar in the mice given the artificial sweeteners, he said. And then, to further test the hypothesis that the intestinal bacteria were to blame, he and his colleagues performed what’s known as a fecal transplant, thus transferring the bacterial ecosystems of sweetener-consuming mice into the guts of mice that had never been exposed to the stuff.
What they found, he said, was that mice never exposed to the sweeteners developed elevated blood sugar after getting transplanted with bacteria from the fake sugar-consuming mice.
The human experiment consisted of two parts. First, the researchers used just 7 subjects who were given a high dose of saccharine. Four of the subjects showed an increase in blood sugar. Then they transferred bacteria from sweetener-consuming humans to sweetener free mice. After the transplants, the mice developed high blood sugar.
The researchers also took bacterial samples from 400 people. While our bacterial colonies are as unique as our fingerprints, the researchers claimed to see a pattern of differences that distinguished regular sweetener users from non-users, though the health implications of this difference are yet to be determined.
Eliniv said it’s not known whether the elevated blood sugar is caused by the increase in some species of bacteria or decrease. You can’t change one thing in your gut ecosystem without a chain reaction of other changes – decreasing one species allows others to expand.
A number of nutritionists have responded by cautioning that the human experiments were a lot less convincing than the ones in mice, and while provocative, didn’t demonstrate that artificial sweeteners cause harm to people. Since we know sugar does contribute to obesity and type 2 diabetes, some said it’s premature to suggest people switch back to regular soda and other sugar-laden foods to satisfy sweet cravings.
“Current epidemiological data in humans do not support a meaningful link between diet drinks and risk for diabetes, whereas sugar rich beverages do appear to be associated with higher diabetes risk. So these findings would not make me choose sugary drinks over diet drinks,” said Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, in a statement for the Science Media Centre, a British nonprofit group. “The findings of this study do not prove that sweeteners pose any real risk to humans. If there are any risks, we need well controlled studies in humans to find them.”
But others, such as University of Chicago immunologist Cathryn Nagler, say the take-home message should be an increased respect for the microbial communities living inside us, and the many ways our present lifestyles may be affecting them.
“They show clearly that the mice fed artificial sweeteners have higher levels of glucose in the bloodstream than those fed glucose,” said Nagler, who wrote a commentary on the findings for the same issue of Nature. “They’ve done a beautiful and elegant set of experiments that for me clearly implicates the microbiota.”
Nagler, who studies the effects of our intestinal bacteria on food allergies says this new work adds to a growing body of evidence connecting trouble in our intestinal communities with diseases that have been increasing at a dramatic rate in the last generation in developed countries. Those include inflammatory bowel disease, food allergies, and obesity. We know something has changed, she said. “We understand more and more how powerful these bacterial communities are and how disturbing the community structure has deleterious consequences for our health.”
Diet is not the only factor that can change your internal zoo. Antibiotic use has had a huge influence, she said, and studies have also shown that babies born by caesarian section start out with different communities from everyone else. Most babies get their first bacterial ecosystem from their mother’s birth canal, but C-section babies get their microbial populations from the skins of the people who first handle them.
Still, the way these bacterial alterations influence our health is yet to be fully explored. In the meantime, many say the study isn’t sufficient to suggest anyone is better off eating sugar or drinking regular sodas.
“Larger scale human studies and funding are urgently required controlling for overall calorie intake,” said Dr Katarina Kos, Senior Lecturer and Consultant in Diabetes and Endocrinology at the University of Exeter in a statement for the Science Centre. “Meanwhile, these findings support the widespread understanding that water is the healthiest drink option.”
