Sucralose has no calories. It can still raise your blood sugar, and not directly: it works through your gut bacteria.
And the response splits from person to person.
Only some of the 120 people saw their blood sugar move
In 2022 the Weizmann Institute in Israel gave 120 healthy adults saccharin, sucralose, aspartame or stevia for two weeks, all below the acceptable daily intake.
All four shifted gut bacteria and blood metabolites. Saccharin and sucralose made blood sugar responses worse.
The next part is the key. When gut bacteria from the strong responders went into germ-free mice, the mice showed the same blood sugar response.
The sweetener did not raise blood sugar itself. The change in gut bacteria did.
A month of sucralose lowered insulin sensitivity
A randomized trial published in 2025 gave sucralose to lean healthy adults for 30 days.
Insulin and glucose after meals went up, insulin sensitivity went down, and gut bacteria lost diversity.
| After 30 days | Direction |
|---|---|
| Post-meal insulin | Up |
| Insulin sensitivity | Down |
| Gut bacteria diversity | Down |
| Butyrate (short-chain fatty acid) | Down |
It is still better than sugar
These studies do not say sucralose is worse than sugar. They say zero calories does not mean nothing happens in your metabolism.
Fill the same glass with sugar and blood sugar climbs far higher, far more reliably.
With diabetes or impaired glucose tolerance, measure your own blood sugar after you change sweeteners. The whole point of these studies is that the response varies by person.
Where you find it
- •Sucralose: zero drinks, protein supplements, syrups, sugar-free gum
- •On the label: "sucralose" or "E955"
- •It is 600 times sweeter than sugar, so products need only a tiny amount
The trick is not to load up on one kind
What caused trouble in the studies was taking one sweetener at the same dose every day for a long stretch.
Sucralose in your drink, stevia in your yogurt, coffee black: split it up and your exposure to any single one drops.
Two weeks is enough for gut bacteria to start shifting. That also means two weeks is enough to shift them back.
Sources · Suez et al., Cell (2022) · Clinical Nutrition ESPEN (2025) randomized trial · JECFA sweetener evaluations