Can I use Re-Lyte Pre-Workout during a fast?

It depends on the type of fast you're doing and your goals.

Re-Lyte Pre-Workout contains 10 calories per serving. Some intermittent fasts (like 5:2 diets and alternate day fasting) involve eating a few hundred calories on fasting days, and Re-Lyte Pre could easily be incorporated into this type of fast.

Other fasts (like the 16/8 method or 24-hour fasts) involve avoiding food altogether for a certain time period. Some fasters only drink water during this fasting window, but others include beverages like black coffee and tea, which contain between 2 and 5 calories per serving. If you're okay with consuming 10 calories during this type of fast, then you could incorporate Re-Lyte Pre-Workout into your fast. 

Another consideration before taking Re-Lyte Pre-Workout during a fast is your caffeine tolerance. Some people are more sensitive to the effects of caffeine on an empty stomach, and Pre-Workout does contain 150 mg of caffeine per serving.