Researchers designed this trial specifically to test the findings of the influential 2014 Suez et al. Nature study. They randomized 46 healthy participants into four groups receiving placebo, pure saccharin at the maximum accepted daily intake (equivalent to about 780 milligrams per day), lactisole (a sweet taste inhibitor), or saccharin plus lactisole for two weeks.

Pure saccharin supplementation did not alter microbial diversity or composition at any level of classification in either humans or mice run in parallel. None of the groups showed changes in glucose or hormonal responses during oral glucose tolerance testing, and mice showed no changes in glucose absorption.

The researchers noted a critical design difference from the 2014 study: Suez and colleagues used commercial saccharin sachets that contained glucose and lactose as fillers, meaning the original results may have been driven by those sugars rather than by saccharin itself. This study used pharmaceutical-grade pure saccharin, eliminating that variable.

Researchers at the University of Manitoba conducted a randomized, double-blinded crossover trial in which 17 healthy adults aged 18 to 45 with normal BMI completed two 14-day treatment periods separated by a 4-week washout. Each participant served as their own control, consuming both the sweetener and placebo in random order.

Doses were set to reflect typical high consumption of pure aspartame and sucralose — the amounts a heavy user would actually consume in daily life. Stool samples were analyzed for microbiota composition and short-chain fatty acid concentrations, while blood tests measured glucose metabolism and insulin sensitivity.

Neither sweetener produced measurable changes in any outcome. Gut bacteria composition, short-chain fatty acid production, and all metabolic markers remained stable throughout both treatment periods. The researchers concluded that at realistic consumption levels, these sweeteners have minimal impact on the gut microbiome in healthy people.

Researchers randomized 34 healthy subjects into two groups: 17 received sucralose capsules at a high dose of 780 milligrams per day (well above typical consumption) and 17 received a placebo for 7 days. The study used a double-blind design to prevent bias.

At the end of the week, the sucralose group showed no differences in glycemic control or insulin resistance compared to the placebo group. Gut microbiome analysis at the phylum level — the broadest classification of bacteria — revealed no changes attributable to sucralose.

The researchers did note that individual variation existed: subjects who happened to have higher insulin responses also tended to have lower Bacteroidetes and higher Firmicutes bacteria, but this pattern was present equally in both the sucralose and placebo groups, meaning it reflected individual differences rather than an effect of the sweetener.

Researchers randomized 27 healthy adults with normal BMI into two groups: 14 consumed stevia drops twice daily and 13 served as controls for 12 weeks — one of the longer intervention periods in sweetener-microbiome research.

Stool samples collected at baseline and week 12 were analyzed using 16S ribosomal RNA gene sequencing, a standard method for profiling gut bacteria. The stevia group showed no significant changes in alpha diversity (the variety of bacteria within each person''s gut) or beta diversity (differences in bacterial communities between people) compared to controls.

No clear differences were detected in the relative abundance of any bacterial groups. While a machine learning classifier could distinguish the two groups with 75% accuracy, this did not translate to clinically meaningful compositional changes. The researchers concluded that stevia does not significantly impact the gut microbiota in healthy individuals.

The U.S. Food and Drug Administration has approved six high-intensity sweeteners as food additives, each with an established acceptable daily intake based on extensive safety testing. These approvals are supported by the European Food Safety Authority and the joint Codex Alimentarius body of the WHO and FAO.

The FDA specifically reviewed studies published since 2023 that linked artificial sweeteners to metabolic disruption and gut microbiome changes. The agency found methodological limitations in these studies and concluded that the current evidence does not support revising existing safety determinations.

The FDA''s position is based on decades of toxicological testing, including multi-generation animal studies, carcinogenicity assessments, and human clinical trials submitted as part of the food additive petition process. The agency notes that approved sweeteners undergo more rigorous pre-market safety evaluation than most food ingredients.

EFSA''s Panel on Food Additives and Nutrient Sources conducted a comprehensive re-evaluation of aspartame safety, the most thorough assessment of any single sweetener by a regulatory body. The panel reviewed all available evidence including animal studies, human clinical trials, and mechanistic data.

A key finding was that aspartame is rapidly broken down (hydrolyzed) in the small intestine into three common components: aspartic acid, phenylalanine, and methanol. These breakdown products are absorbed into the bloodstream before food reaches the large intestine, where the vast majority of gut bacteria reside.

Because aspartame does not reach the colon intact, EFSA concluded it is unlikely to interact meaningfully with the colonic microbiota. The panel found no safety concerns at the current accepted daily intake of 40 milligrams per kilogram of body weight per day — a level that would require a 70-kilogram adult to consume roughly 14 cans of diet soda daily to reach.

The SWEET consortium conducted a multicenter randomized controlled trial across multiple European countries, the longest randomized trial to date examining sweetener effects on the gut microbiome. Adults with overweight or obesity were randomly assigned to either use sweeteners and sweetness enhancers or avoid them entirely for one year.

At the 1-year mark, the sweetener group had maintained more weight loss than the control group. Their gut microbiota composition had changed in a direction generally considered beneficial: levels of bacteria that produce short-chain fatty acids and methane increased. Short-chain fatty acids are the main fuel source for cells lining the colon and play a key role in gut health and immune function.

No adverse effects on cardiometabolic risk markers were observed. The researchers did note higher self-reported gastrointestinal side effects (such as bloating) in the sweetener group, but these did not correspond to negative changes in measured microbiome or metabolic outcomes.

Researchers at the USDA Agricultural Research Service tested the effects of steviol glycosides (the active compounds in stevia) and erythritol (a sugar alcohol) on human gut bacteria using an advanced laboratory model that simulates conditions in the human colon.

Neither sweetener negatively impacted bacterial growth. Erythritol enhanced the production of butyric acid and pentanoic acid, both short-chain fatty acids that nourish colon cells, reduce inflammation, and strengthen the gut barrier. Stevia was easily broken down by gut bacteria and increased the density of several health-supporting bacterial species.

These findings suggest that not only do some sweeteners avoid harming gut bacteria, they may actually support gut health in ways similar to prebiotics — dietary fibers that feed beneficial bacteria. The results highlight that different sweeteners have very different biological effects and should not be treated as a single category when evaluating gut health impacts.