What do artificial sweeteners do to your gut microbiome?

Mouse studies, including a well-known study from the Weizmann Institute, show that artificial sweeteners can disrupt the composition of the gut microbiome. In those experiments, mice developed poorer blood sugar regulation after consuming sweeteners. This effect disappeared once the animals were given antibiotics, and it could be transferred via faecal transplants to germ-free mice. That points to the gut microbiome as the link, not the sweetener itself. A similar pattern was seen in a small group of people, but how large this effect is in humans remains unclear.

On the other hand, a small randomised study in 17 healthy adults found no measurable change in the gut microbiome or in the production of fatty acids made by gut bacteria, after fourteen days of consuming aspartame or sucralose in high but realistic amounts. There is therefore no clear-cut outcome: one study does see an effect, another does not. That makes it difficult to draw firm conclusions.

Several review studies signal that sweeteners may contribute, via the gut microbiome, to insulin resistance and poorer blood sugar regulation. Which sweeteners carry that risk and at what amounts has not yet been established. Saccharin, sucralose and acesulfame-K are mentioned most often in animal research, but comparable evidence in humans is still largely lacking.

A large population study found an association between high sweetener consumption and a greater risk of cardiovascular disease, cancer and mortality. That is an association, not proof of a causal relationship: people who consume a lot of sweeteners may also live less healthily in other ways. The same applies to associations with gastrointestinal complaints and fatty liver disease that emerge from observational research.