What the WHO Actually Said
In May 2023, the WHO published its first formal guideline on non-sugar sweeteners. The conclusion was careful but significant: non-sugar sweeteners do not confer any long-term benefit in reducing body fat in adults or children, and long-term use may carry potential undesirable effects.
The guideline covers all common non-sugar sweeteners including acesulfame K, aspartame, saccharin, and sucralose. It is based on a systematic review of 45 randomised controlled trials and multiple prospective cohort studies. The finding was not that these sweeteners are definitively harmful. The finding was that the health rationale for using them instead of sugar is not supported by the evidence.
Replacing sugar with a sweetener does not solve the problem. It reroutes it.
What They Do to Your Gut Microbiome
This is where the science gets genuinely interesting, and where the research is still evolving. Artificial sweeteners pass through the digestive system largely unabsorbed. They arrive in the colon intact, where they encounter the trillions of bacteria that make up the gut microbiome. What happens next varies by sweetener, by individual, and by dose.
A 2023 systematic review published in PMC, covering 117 studies on acesulfame K, aspartame, saccharin, and sucralose, found that each of these sweeteners altered gut microbiota composition in ways associated with dysbiosis, including reduced diversity of beneficial bacteria. The effects were not uniform across sweeteners or individuals, but the direction was consistent: disruption, not neutrality.
A 2025 study published in Frontiers in Microbiology, examining five common sweeteners using minibioreactor arrays that model the human gut, found that synthetic sweeteners reduced gut microbiome diversity more significantly than non-synthetic alternatives. Not all sweeteners behaved the same way. The type matters.
The Three Artificial Sweeteners Most Australians Use Daily
Here is what the current evidence says about each.
The most studied and most controversial. In 2023, the International Agency for Research on Cancer classified aspartame as a Group 2B carcinogen, meaning there is limited evidence of possible carcinogenicity in humans. Harvard Chan School researchers note this classification sits in the same category as aloe vera extract and pickled vegetables, meaning the evidence is limited, not conclusive. Gut research shows it alters the balance of bacteria in ways that may affect glucose tolerance.
Widely used in diet products and marketed as inert because it passes through the body undigested. The research suggests it is not inert in the gut. Studies show sucralose reduces beneficial bacterial populations and may disrupt gut barrier function, particularly with sustained high-dose use. Individual responses vary considerably.
The oldest artificial sweetener in widespread use. A 2022 study published in Cell by Weizmann Institute researchers found that saccharin consumption in healthy adults significantly altered gut microbiota and impaired glucose tolerance in some participants within two weeks. The effect was highly individual, which the authors attributed to differences in baseline microbiome composition.
What This Means in Practice
The honest summary is this. Artificial sweeteners are not as safe as they were once assumed to be. They are probably not as harmful as the most alarming headlines suggest. The gut microbiome research is accumulating faster than the public health guidance can absorb it, and the picture is still being clarified.
What is clear is that the assumption of neutrality is not supported by the current science. The idea that replacing sugar with a sweetener is a simple, consequence-free swap has not held up to scrutiny. The gut encounters these compounds. The microbiome responds to them. Whether and how significantly depends on the sweetener, the dose, the duration, and the individual's baseline gut composition.
The question is not just "does it have calories?" It is "what does it do to the bacteria that govern your gut?"
A Different Way to Think About the Sweet Swap
DULCI does not contain artificial sweeteners. It uses the premium fraction of the stevia plant. The rare, expensive molecule that makes up less than 0.1% of the leaf and that peer-reviewed sensory research shows produces sweetness indistinguishable from sugar without the bitterness associated with cheaper stevia fractions.
More importantly, it adds something rather than just removing something. 7g of clinically studied prebiotic fibre per scoop, an excellent source of fibre by the regulated standard. Rather than substituting sweetness with a compound that disrupts the microbiome, DULCI feeds the bacteria that keep the microbiome functioning well. Zero artificial ingredients. A daily deposit into gut health, not a withdrawal from it.
The artificial sweetener era produced better-tasting diet products and worse gut science. The two things happened simultaneously, and nobody connected them for long enough.
The science is connecting them now.
