New Studies Cast Doubt on Artificial Sweeteners
As rates of obesity, diabetes, insulin resistance, and metabolic syndrome reach epidemic proportions, artificial sweeteners have been utilized to tame the public’s sweet tooth while simultaneously reducing its consumption of added sugar and nutritionally-vapid calories.
However, since the discovery of saccharin in 1879, artificial sweeteners have been the subject of controversy, often decried as toxic, harmful, and hazardous to our health. Yet, numerous studies have shown that these “fake sugars” are safe and non-toxic when consumed in appropriate amounts. 
Related - Can Sucralose Cause Weight Gain?
But, a pair of recent studies have once again cast a shadow of suspicion on these non-nutritive sweeteners, suggesting that they may cause significant changes in the composition of our gut microbiome.
Let’s discuss these new studies and see what we can gather from their findings.
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New Artificial Sweetener Studies
A coalition of researchers from the Ben-Gurion University of the Negev in Israel and Nanyang Technological University in Singapore set out to investigate the “relative toxicity” of six FDA-approved artificial sweeteners along with 10 sports supplements that incorporated the sweeteners. 
Included in the six were:
Names of the 10 sports supplements used in the trial were not noted directly in the study, but their supplement facts were detailed. 
For the tests, the researchers developed a bacterial sensing model comprised of strands of E. coli that had been genetically modified to produce light (bioluminesce) when they came into contact with toxicants. Researchers believed these strands were representative of the broad complex of bacteria residing in our gut.
Ariel Kushmaro, one of the researchers on the team, noted:
"We modified bioluminescent E. coli bacteria, which luminesce when they detect toxicants and act as a sensing model representative of the complex microbial system.” 
Basically, researchers “tweaked” three different strands of bacteria to light up if its DNA was damaged or if its cell walls were damaged.
To test the effects of the various sweeteners, researchers bred cultures of E. coli, put them in test tubes, then applied artificial sweeteners directly to the bacteria at concentrations far beyond what is typically found in a serving of diet soda.
At the end of the trial, researchers documented that all six artificial sweeteners damaged the bacteria, but the manner in which each sweetener affected the bacteria differed. Some affected growth rate while others impacted bioluminescence.
Following publication of the results, most news outlets branded the study and its findings as:
"Artificial sweeteners have toxic effects on gut microbes." 
Commenting on the findings of the study, senior author of the study, Evgeni Eltzov, noted that the results of this trial DO NOT show that artificial sweeteners are toxic to humans. What the results show, according to Eltzov, is that artificial sweeteners have the potential to damage bacteria. 
Furthermore, Dr. Kristina Rother, a senior research physician at the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health who was not a member of the research team, commented that:
“...the lab experiment's results don't translate directly to humans. For example, the concentrations of artificial sweetener presented to the bacteria were higher than what a person would consume in a can of diet soda…”
In an interview with Live Science, Dr. Rother continued to explain that the human gut contains a rather extensive and diverse system of bacteria, not just E. coli. She continued, by saying this study, “doesn't tell us what happens in real life. It tells us what happens in a test tube...Real life is just more complicated." 
In other words, the results of a cell culture study using doses much higher than you’d typically ingest don’t carry over to what happens when you ingest artificial sweeteners in your daily can of diet soda. They might affect the gut bacteria, but so does everything else you eat. And, furthermore, while artificial sweeteners “affect” or “change” gut bacteria, the jury is still out on whether or not these changes are for better or worse. We simply don’t have enough understanding or data of the human gut microbiome to make such determinations.
Now, let’s look at the second study and see what it shows.
The second new study into the potential pitfalls of artificial sweetener consumption was presented at the annual meeting of the European Association for the Study of Diabetes.  Using a rather small test group of 29 non-diabetic subjects (age 30 ± 2 years), researchers randomized the individuals in a double-blind fashion to receive either a capsule containing a combination of artificial sweeteners or placebo.
The group receiving the artificial sweetener capsule received a combination of 92 mg sucralose + 52 mg acesulfame-K in capsule form three times per day for two weeks. FYI, this amount of sweetener is what you’d get in roughly 50 ounces (1.5 liters) of diet soda per day.
For the study, researchers were interested in what the artificial sweeteners did to the subjects’ glycemic control and their gut microbiome. After two weeks, the researchers documented two significant changes in the gut bacteria of those who consumed the capsules filled with the combination of sucralose and Ace-K.
Specifically, those consuming the artificial sweeteners experienced “greater variation in faecal microbiota composition, along with a significant reduction in the health-associated bacterium Eubacterium cylindroides.” 
In other words, researchers found that consuming artificial sweeteners changes what bacteria are present in your poop and noted a decrease in the presence of Eubacterium cylindroides, a species of bacteria associated with gut health.
Researchers also noted a stark increase in “11 opportunistic gut pathogens", which the researchers state aren’t typically found in the guts of healthy individuals.
The study also found that consuming artificial sweeteners for two weeks straight impacted how test subjects responded to glucose. In the abstract, the researchers state:
"The observed decrease in fermentative bacteria populations and changes in the pathways used by bacteria to harvest energy predicted a deterioration in the body's ability to regulate glucose."
Basically, the authors are stating that consumption of artificial sweeteners impaired the body’s ability to control glucose.
It’s important to note that this study has yet to be peer-reviewed or published, meaning reviewers could find some glaring errors in the study, its methods, analysis, or results. Also of note is that only the abstract of the study is available to the public, not the complete study.
Discussing the findings of the study, Navel Sattar, a professor at the University of Glasgow who was not involved with the study remarked: 
"This study, whilst well done, is not the same as taking one or two diet drinks (containing sweeteners) per day, more often than not with food, but rather is equivalent to almost five cans of diet drinks every day for two weeks – given in the form of tablets. Also, we don't know what these gut marker changes really mean for health so it's all highly speculative, and there are no clear data in humans that sweeteners alter blood sugar levels in the way that is speculated by the authors."
Another expert on the matter, Dr Katarina Kos, Senior Lecturer in Diabetes and Obesity, University of Exeter, stated: 
“Where does this leave us for now. It is too early to be concerned about a potential increased risk in diabetes as result of use of artificial sweeteners and results from this study and further research is needed to validate this. Thus guided from previous work and until we know better, we should approach sweetened drinks and food with the awareness that it may want us to ‘compensate’ with further calorie intake. The best option for those concerned may remain water as a zero calorie drink.”
And, noted endocrinologist, Kevin Murphy, from Imperial College London, also stated his concerns regarding the latest research findings, saying:
"Further work is needed to confirm whether this altered bacterial activity is actually responsible for the impaired glucose control observed – the work as described cannot demonstrate a causal effect.”
So, what do these findings tell us and how do they carry over to our everyday life?
Basically, we don’t really know.
Exposing bacteria strains in a test tube to truckloads of artificial sweeteners is a far cry from ingesting one or two diet sodas per day within the context of an otherwise healthy diet. The dosages used in the study were roughly equal to 1000mg/L of sucralose and 2000mg/L of saccharin. You’d have to consume around 6 liters of diet soda per day to approach those levels.
And besides that, these sweeteners were tested only on E. coli. Our guts contain substantially greater amounts and diversity of bacteria than simply E. Coli.
Remember, the dose makes the poison. Water can kill you if consumed in large enough quantities.
The results of these studies should encourage more research to be done on humans consuming reasonable amounts of artificial sweeteners within the confines of a healthy diet. They should not be used to generate a bunch of click-bait articles under the guise of “artificial sweeteners destroy and maim your gut.”
1) Harpaz, D., Yeo, L. P., Cecchini, F., Koon, T. H. P., Kushmaro, A., Tok, A. I. Y., Eltsov, E. (2018). Measuring Artificial Sweeteners Toxicity Using a Bioluminescent Bacterial Panel. Molecules, 23(10). https://doi.org/10.3390/molecules23102454
2) "Artificial Sweeteners Have Toxic Effects on Gut Microbes." ScienceDaily, 11 Oct. 2018, www.sciencedaily.com/releases/2018/10/181001101932.htm.
3) "No, Drinking Diet Soda Won't Poison Your Gut Bacteria, But It Could Do Harm." Live Science, Oct. 3, www.livescience.com/63743-artificial-sweeteners-gut-health.html.
4) R.L. Young, D. Kreuch, F.M. Mobegi, et al. Low-calorie sweeteners disrupt the gut microbiome in healthy subjects in association with impaired glycaemic control. European Association for the Study of Diabetes (EASD) 2018 Annual Meeting; October 5, 2018; Berlin, Germany. Abstract 241.
5) "Expert Reaction to Conference Abstract on Low-calorie Sweeteners, Gut Bacteria and Blood Sugar Control | Science Media Centre." Science Media Centre, 5 2018, www.sciencemediacentre.org/expert-reaction-to-conference-abstract-on-low-calorie-sweeteners-gut-bacteria-and-blood-sugar-control/.
6) Magnuson, B. A., Roberts, A., & Nestmann, E. R. (2017). Critical review of the current literature on the safety of sucralose. Food and Chemical Toxicology, 106, 324–355. https://doi.org/https://doi.org/10.1016/j.fct.2017.05.047
7) Aguilar, F., Autrup, H., Barlow, S., Castle, L., Crebelli, R., Engel, K., … Toldrá, F. (2008). Scientific Opinion of the Panel on Food Additives ,Flavourings , Processing Aids and Materials in Contact with Food. The EFSA Journal, 581, 1–29. https://doi.org/10.2903/j.efsa.2007.581
8) Bassoli, A., & Merlini, L. (2003). SWEETENERS | Intensive. In B. B. T.-E. of F. S. and N. (Second E. Caballero (Ed.) (pp. 5688–5695). Oxford: Academic Press. https://doi.org/https://doi.org/10.1016/B0-12-227055-X/01172-X
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