Artificial sweeteners are meant to help control our blood sugar and avoid weight gain - but recent studies have linked them to everything from Type 2 diabetes to heart disease. Still, scientists have struggled to work out exactly how they’re affecting us - our bodies can’t actually digest artificial sweeteners, which is why they’re calorie free, so what’s going on?
This new research in humans and mice, led by scientists from the Weizmann Institute of Science in Israel, suggests that artificial sweeteners may actually be messing with our gut bacteria and triggering glucose intolerance in the body - which is the first step towards metabolic syndrome and adult-onset diabetes. The research is published in Nature.
"Our results suggest that in a subset of individuals, artificial sweeteners may affect the composition and function of the gut microbiome,” Eran Elinav, an immunologist and co-author of the study, explained at a press conference.
To understand the link between sweeteners and blood sugar levels, the scientists looked at three common artificial sweeteners - aspartame, sucralose and saccharin - and found that all of them caused a change in blood sugar levels in mice. Interestingly, this change in blood sugar was higher than the one seen in mice who ate normal sugar.
The researchers then investigated the impact the sweeteners were having on the gut bacteria of the mice by giving antibiotics to mice who had been fed artificial sweeteners. This effectively wiped out all of their gut bacteria - and, interestingly, caused their blood sugar levels to go back to normal.
In another experiment, the researchers transplanted the gut-bacteria-filled faeces of a group of mice who had been regularly fed sweeteners into mice who had never eaten artificial sweeteners. The mice that received the transplants experienced strangely high blood sugar, similar to the levels seen in the mice who had eaten artificial sweeteners - even though they’d never touched the stuff themselves.
Genetic research took the evidence a step further, as journalist Arielle Duhaime-Ross writes for The Verge, and showed that bacterial function was changed in response to altered gut microbes - a potential mechanism that could explain the high blood sugar trigger.
As a Weizmann Institute of Science press release explains: “This, in itself, was conclusive proof that changes to the gut bacteria are directly responsible for the harmful effects to their host's metabolism. The group even found that incubating the microbiota outside the body, together with artificial sweeteners, was sufficient to induce glucose intolerance.”
Based on this strong causal evidence in mice, the researchers performed smaller scale studies in humans - one involved looking at the blood sugar levels and gut bacteria of 381 participants. As expected, those who self-rated that they ate a lot of sweeteners had disturbances in several metabolic indicators - including changes in their gut bacteria and increased weight.
A second study was even more interesting, and followed seven people who don’t normally eat artificial sweeteners for a week. Half of them were given sweeteners and, as Duhaime-Ross explains for The Verge, after just four days there were microbial changes in the guts of most of them and an increase in blood sugar levels. However, not everyone responded in the same way - and analysis of gut microbes explained the difference. It appears there are two different populations of human gut bacteria out there - one that induces glucose intolerance when it’s exposed to sweeteners, and another that doesn’t react.
“Elinav believes that certain bacteria in the guts of those who developed glucose intolerance reacted to the chemical sweeteners by secreting substances that then provoked an inflammatory response similar to sugar overdose, promoting changes in the body's ability to utilise sugar,” the press release explains.
However, although the results are significant, more work needs to be done in humans before the scientists can recommend that people change their diets. Some critics have argued that the study fed the participants too high a level of artificial sweeteners. But Susan Swithers, a behavioural neuroscientist at Purdue University in the US who wasn’t involved in the research, told The Verge via email: “People need to be much more mindful of what they are eating and drinking and make efforts to avoid products that have added sweeteners in any form.”
The next step is to reproduce these findings in more humans and try to understand why some gut bacteria are affected and others aren’t. And from there we can determine what role sweeteners will play in our future diets. "The work is important," Swithers told The Verge, "because it underscores the role that artificial sweeteners may play in contributing to the very problems they were designed to help."