Do sweeteners break a fast?

Sweetener by sweetener

Sweetener	Calories	While fasting
Stevia, monk fruit	None	No insulin spike in a trial 2; fine in small amounts
Sucralose	None	No spike on its own 1; daily use for weeks lowered insulin sensitivity 3,4
Aspartame	Practically none at the amounts used	No spike in a trial 2
Erythritol	None 5	Unlikely to affect your fast; long-term safety is an open question 6
Xylitol, sorbitol, maltitol	About 2.4 per gram 5	A little, as in gum, is fine; larger amounts add up
Tabletop packets and syrups	Check the label	Often contain dextrose or maltodextrin, which are sugars
Honey, agave, coconut sugar	Like sugar	Break your fast

On the day: no insulin spike

In a British trial, swallowing sucralose didn't raise insulin or gut hormones, and simply tasting it and spitting it out had no effect either ¹. In Singapore, drinks sweetened with aspartame, stevia or monk fruit didn't cause the rise in blood sugar and insulin that a sugary drink did ². A sweetened coffee or diet drink won't undo your fast.

The catch: real sugar and daily habits

Things look different when a sweetener meets real sugar. In people with obesity who didn't usually have sweeteners, a sucralose drink taken before a glucose drink raised the insulin response by 20% ⁷. And the effect seems to build with time.

These were small, short trials, and they don't prove that sweeteners harm you. They are a good reason not to rely on sweet drinks to get through every fast.

Erythritol: zero calories, one open question

Erythritol is counted as zero calories on food labels in the EU ⁵, which makes it popular in low-sugar products. In 2023, researchers found that people with more erythritol in their blood had more heart attacks and strokes over three years, and in 8 healthy volunteers an erythritol drink kept blood levels high for more than two days ⁶. The people studied were already being checked for heart disease, and a link like this can't show cause and effect. It's a reason for moderation, not alarm.

Do sweeteners help you lose weight?

Not as much as you'd hope. In 2023 the World Health Organization advised against using non-sugar sweeteners to control weight, after a review found no long-term benefit for body fat. It's a conditional recommendation, and it doesn't apply to people who already have diabetes ⁸. In the Singapore trial, people who had a sweetened drink simply ate more at lunch ².

MYTH

Sweet taste alone makes your body release insulin.

FACT

In a British trial, tasting sucralose and spitting it out didn't change insulin or gut hormones, and swallowing it didn't either ¹.

The practical answer: if a sweetened coffee helps you reach your goal, it won't undo your fast. Aim to need it less over time. Water, sparkling water, black coffee and plain tea are the cleanest choices.

Sources

1. Ford HE, Peters V, Martin NM, et al. Effects of oral ingestion of sucralose on gut hormone response and appetite in healthy normal-weight subjects. Eur J Clin Nutr. 2011;65(4):508-13. doi.org/10.1038/ejcn.2010.291
2. Tey SL, Salleh NB, Henry J, et al. Effects of aspartame-, monk fruit-, stevia- and sucrose-sweetened beverages on postprandial glucose, insulin and energy intake. Int J Obes (Lond). 2017;41(3):450-457. doi.org/10.1038/ijo.2016.225
3. Romo-Romo A, Aguilar-Salinas CA, Brito-Córdova GX, et al. Sucralose decreases insulin sensitivity in healthy subjects: a randomized controlled trial. Am J Clin Nutr. 2018;108(3):485-491. doi.org/10.1093/ajcn/nqy152
4. Lertrit A, Srimachai S, Saetung S, et al. Effects of sucralose on insulin and glucagon-like peptide-1 secretion in healthy subjects: a randomized, double-blind, placebo-controlled trial. Nutrition. 2018;55-56:125-130. doi.org/10.1016/j.nut.2018.04.001
5. Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIV: conversion factors for the calculation of energy. www.legislation.gov.uk/eur/2011/1169/annex/XIV
6. Witkowski M, Nemet I, Alamri H, et al. The artificial sweetener erythritol and cardiovascular event risk. Nat Med. 2023;29(3):710-718. doi.org/10.1038/s41591-023-02223-9
7. Pepino MY, Tiemann CD, Patterson BW, et al. Sucralose affects glycemic and hormonal responses to an oral glucose load. Diabetes Care. 2013;36(9):2530-5. doi.org/10.2337/dc12-2221
8. World Health Organization. WHO advises not to use non-sugar sweeteners for weight control in newly released guideline. 15 May 2023. www.who.int/news/item/15-05-2023-who-advises-not-to-use-non-sugar-sweeteners-for-weight-control-in-newly-released-guideline