Sweeteners and gut microbiota

It has previously been reported that sweeteners are harmful to the gut microbiota, through their ability to alter the composition and function of the microorganisms in a way that may disrupt glucose tolerance.1  This study gained media attention, and headlines such as ‘Artificial sweeteners have toxic effects on gut microbes2 quickly spread.

Sweeteners and gut microbiota

A recent review by Lobach et al. has critically evaluated the body of research looking at the effects of low/no-calorie sweeteners (LNCS) on the gut microbiota. They concluded that there is no clear evidence for this relationship3, in opposition to previous findings1.  In the review, the authors identified 17 publications in humans and animals that investigated the effects that LNCS administration had on the gut microbiota. The sweeteners used include: acesulfame K, aspartame, cyclamate, neotame, saccharin, sucralose, and rebaudioside A.

There were only two studies that investigated the effects of LNCS in humans1,4.  Firstly, a cross-sectional study (n=31) found the overall bacterial diversity to be different between consumers and non-consumers of sweeteners (Acesulfame K, Aspartame). However, the reviewers highlighted that habitual diet was not controlled for and so it is not possible to conclude that the differences were caused by sweeteners4.  Secondly, an intervention study (n=7) found changes in the gut microbiota of subjects after 1-week of consuming saccharin, but only in those who had a change in glycaemic response during the intervention. The reviewers highlighted that again, habitual diet was not controlled for, there was no control group, participants were arbitrarily grouped based on their glycaemic responses, and the microbiotas were different between the groups at baseline. Due to these reasons, it is not possible to conclude a cause and effect relationship between sweeteners and the gut microbiota. 

The remaining studies included were conducted in animals. Although changes to the gut microbiota were observed in some, the reviewers highlighted a number of limitations to the study designs. The studies often used doses that exceed the current acceptable daily intakes (ADI), in some cases as much as 2000 times more5.  In studies that did administer an appropriate dose of sweeteners, either there was no change to the gut microbiota, or the study was confounded because diet wasn’t controlled for. The reviewers highlighted that diet was the main confounding factor in most of these studies. Therefore, if this was not controlled for, we cannot conclude the causative effects of sweeteners on the gut microbiota.

In addition to critically appraising the research, the reviewers also described the molecular and metabolic mechanisms to support LNCS’s inability to affect the gut microbiota. Some LNCS are rapidly absorbed in the small intestine and do not interact with the gut microbiota in the colon, some are largely unabsorbed and undigested in the gut, and some do not undergo gastrointestinal metabolism and are excreted unchanged in the urine.

With public health strategies aiming to reduce the nation’s sugar consumption, it is possible that peoples’ intakes of sweeteners may increase as a result. The findings from this review suggest that there is no clear evidence that LNCS affects the gut microbiota, nor are there plausible mechanisms for them to do so.

Read the full open-access paper here.


1. Suez et al. (2014) Nature 514(7521):181-186.

2. https://www.sciencedaily.com/releases/2018/10/181001101932.htm

3. Lobach et al. (2019) Food and Chemical Toxicology 124:385-399

4. Frankenfeld et al. (2015) Ann Epidemiol 25:736-742 

5. Anderson and Kirkland (1980) Food Chem Toxicol 18:353-555