Brushing teeth or using mouthwash does not break a fast because it does not initiate stomach processing or increase insulin and blood glucose.

“Does toothpaste start the clock? If they're not swallowing. So if you're not swallowing it, probably not starting the clock. Yeah. Yeah. It's not starting, it's actually resetting the clock. Resetting. So I think we have to also think of time-restricted feeding, although we came from a circadian clock lab. So that's why we always get connected with circadian with circadian clock. But time-restricted eating has also feeding, fasting, that whole physiology type to it. So the other way to ask the question is, "Does brushing your teeth or mouthwash break the traditional definition of fasting?" And definitely it's not breaking that, it's not putting food in your stomach so that the stomach will start processing it and insulin starts going up slightly and blood glucose going up.”