Non-Caloric Sweeteners

Non-caloric sweeteners do not break a fast in the strict sense of adding calories, but they are not all equally neutral, and the outcome depends on which sweetener and which fasting goal you aim to achieve. Stevia, monk fruit, and erythritol are the dependable choices for a fast, while sucralose, saccharin, and aspartame are probably fine in small amounts but have not been shown to be completely inert.

The difference is in how the body handles them. Erythritol is a sugar alcohol that is absorbed and then excreted largely unchanged rather than used for energy, while stevia and monk fruit are plant-derived sweeteners that do not raise glucose or insulin in short-term studies. None of the three provides calories or triggers a meaningful insulin response, so they do not break a fast, and they are not known to interfere with autophagy, the cell's repair process that depends on calories and insulin staying low. The artificial sweeteners are where the open questions remain: some research has linked sucralose, saccharin, and aspartame to changes in glucose tolerance through effects on the gut microbiome, a finding that is debated and not seen in everyone, which is why they cannot yet be called completely inert.

For that reason, if you use a sweetener during a fast, stevia, monk fruit, and erythritol are the reliable options, and it is the artificial sweeteners, not the category as a whole, that warrant caution.

Source: Suez et al., artificial sweeteners and glucose tolerance, Nature (2014)