📚 Part of our Blood Sugar Guide — an evidence-based guide.
Artificial sweeteners have no calories and do not raise blood glucose directly. For years that made them look like a straightforward win. The current evidence is messier, and the honest answer depends heavily on what you are comparing them to.
What they do and do not do
Non-nutritive sweeteners bind sweet taste receptors far more strongly than sugar, so tiny amounts suffice. They are not metabolised for energy, so they do not raise blood glucose or insulin the way sugar does. That much is well established and is why they are used in diabetes management.
The debate is entirely about indirect effects.
The gut microbiome question
This is the most cited concern. A 2014 mouse study found saccharin altered gut bacteria and induced glucose intolerance, with a small human sub-study suggesting similar effects in some participants.
A 2022 human trial went further, giving four sweeteners to healthy adults and finding that saccharin and sucralose impaired glucose tolerance, with microbiome changes, while aspartame and stevia did not — and responses varied substantially between individuals.
Real findings, worth taking seriously. But they involve small numbers, short durations, doses at the upper end of typical intake, and effects that differ by sweetener and by person. They do not establish that sweetener use causes diabetes.
Observational studies and their problem
Cohort studies repeatedly associate diet soda consumption with obesity, type 2 diabetes and cardiovascular disease. These findings are heavily affected by reverse causation: people switch to diet drinks because they have gained weight or been told to watch their sugar. The exposure follows the condition.
Randomised trials tell a different story. Trials substituting non-nutritive sweetened beverages for sugar-sweetened ones generally find modest weight loss or weight maintenance compared with sugar. That is the comparison that matters for someone currently drinking sugar.
The WHO guidance, read properly
The WHO issued a 2023 recommendation against using non-sugar sweeteners for weight control. It is often reported as “WHO says sweeteners are unhealthy”, which is a distortion.
The guidance was conditional, based on low-certainty evidence, and specifically about using sweeteners as a long-term weight control strategy. It did not conclude they are harmful, and it explicitly did not apply to people with diabetes.
Separately, the IARC classified aspartame as “possibly carcinogenic to humans” (Group 2B) in 2023 — a category based on limited evidence that also contains aloe vera and pickled vegetables. The accompanying JECFA review kept the acceptable daily intake unchanged, at a level equating to well over a dozen cans of diet soda daily for an average adult.
A workable position
If you currently drink sugar-sweetened beverages, switching to diet versions is very likely an improvement. Liquid sugar is among the clearest dietary harms there is (why).
If you already drink water, there is no reason to start.
Treating sweeteners as a transitional tool — a step from sugar toward water, sparkling water or unsweetened tea — is more sensible than treating them as a destination. And if you are concerned, the trial evidence is most reassuring for aspartame and stevia, less so for saccharin and sucralose.
One thing to avoid entirely: assuming a sugar-free label makes a food healthy. Sugar-free biscuits are still biscuits.
When to see a doctor
Ask for an A1C or fasting glucose if you have not been tested in three years or carry excess weight around the middle. People with phenylketonuria must avoid aspartame entirely. And discuss sweetener use in pregnancy with your doctor, where evidence is more limited.
The honest bottom line
Artificial sweeteners do not raise blood sugar directly. Some — saccharin and sucralose in particular — may affect the gut microbiome and glucose tolerance in some people, on short, small, high-dose evidence. Observational links to disease are badly confounded by reverse causation, and randomised trials favour sweeteners over sugar. Compared with sugar they are better; compared with water they are not. The WHO advice was conditional, low-certainty, and not about diabetes.
A mouse study has since reported effects carrying into later generations: why that headline is about mice.
Frequently asked questions
Are artificial sweeteners bad for your blood sugar?
They don't spike blood sugar directly the way sugar does, but research is mixed on their long-term metabolic effects, and some may affect the gut microbiome and glucose tolerance in certain people.
Is diet soda better than regular soda?
For blood sugar and calories in the moment, diet soda avoids the sugar hit of regular soda. But it isn't a health drink — water or unsweetened options are the better long-term habit.
Does the WHO recommend artificial sweeteners for weight loss?
No. In 2023 the World Health Organization advised against using non-sugar sweeteners for weight control, citing a lack of long-term benefit and possible risks.