Does sucralose break a fast?
Sucralose is the sweetener with the most reason for caution. It contains no calories, and pooled trial evidence finds no meaningful effect on postprandial glucose or insulin — but a randomised controlled trial in healthy subjects found sucralose decreased insulin sensitivity, and that finding has not been explained away. Retail Splenda is also bulked with maltodextrin, which is straightforwardly a carbohydrate.
| Fasting for | Verdict | Why |
|---|---|---|
| Weight loss | Depends | Pure sucralose is calorie-free. Splenda packets contain maltodextrin and are roughly 3 kcal each — trivial once, not trivial at ten a day. |
| Autophagy | Depends | No protein or energy, but this is the sweetener with a documented metabolic effect. If you are fasting strictly, this is the one to drop first. |
| Blood work | Breaks it | Water only before a fasting blood test. |
| Ketosis | Depends | Pure sucralose contains no carbohydrate. The maltodextrin in packet Splenda does, in small amounts. |
| Gut rest | Depends | Reported to cause digestive symptoms in some people at higher intakes. |
Why
Sucralose is a chlorinated sucrose derivative that is largely unabsorbed and yields no energy, so on the calorie test it passes. The reason it gets a more cautious verdict than stevia or monk fruit is a direct one: a randomised controlled trial reported that sucralose decreased insulin sensitivity in healthy subjects. A separate randomised, double-blind, placebo-controlled trial examining sucralose’s effect on insulin and GLP-1 secretion adds to a mixed picture rather than settling it, and the broader network meta-analysis of non-nutritively sweetened beverages finds no consistent postprandial effect across the class. The fair reading is that the class as a whole looks quiet, sucralose specifically has a contrary randomised finding, and that is enough to name it rather than average it away.
0 kcal for pure sucralose. Approximately 3 kcal per Splenda packet.
The exceptions
This is usually where the real question lives.
- Splenda in packets and bags is bulked with maltodextrin and dextrose. The sachet is not pure sucralose.
- Sucralose is heat-stable and appears in baked goods, protein powders and medications you may not think of as sweetened.
- Liquid sucralose drops avoid the bulking agents.
- If you want to keep a sweetener during a fast and you care about the metabolic evidence, stevia and monk fruit currently have the cleaner record.
Sources
- Sucralose decreases insulin sensitivity in healthy subjects: a randomized controlled trial — Am J Clin Nutr, 2018PMID 30535090
- Effects of sucralose on insulin and glucagon-like peptide-1 secretion in healthy subjects: a randomized, double-blind, placebo-controlled trial — Nutrition, 2018PMID 30005329
- The Effect of Non-Nutritive Sweetened Beverages on Postprandial Glycemic and Endocrine Responses: A Systematic Review and Network Meta-Analysis — Nutrients, 2023PMID 36839408
No clinician reviews this site. Sources on this entry were verified by the author, who is not a doctor or a dietitian — what that means.
Last updated 2026-08-15.
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