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Yes, plain sparkling water is fine during most fasting windows because it has no calories, but sweetened or flavored bubbly drinks can break a fast.

No, drinking a protein shake breaks a fast, because protein, calories, and sweeteners stimulate insulin and stop the zero-calorie fasting state.

Yes, blended smoothies usually fit a full liquid fast when fully strained and milkshake-smooth, but they don’t fit a strict clear-liquid fast before surgery.

Skimmed milk during a fasting window still has calories and lactose, so even a splash usually ends the fast by kicking your body into feeding mode.

Yes, plain seltzer with no calories or sweeteners fits most intermittent fasting rules, but sugary or boosted cans can end the fasting window.

Yes, most zero-calorie pre workout in a fasted state won’t raise insulin, but sugary mixes or amino-heavy blends can end a fasting window.

Yes, a splash of milk in tea adds calories that can pause a strict fast, but many people who use intermittent fasting for weight control still allow 10–20 milk

Yes, you can drink Pepsi Max during most fasting windows for weight loss since it has 0 calories, but strict fasts for autophagy or gut rest call for plain

Yes, monk fruit sweetener usually doesn’t break a fast, because pure monk fruit extract has no sugar or calories and barely moves insulin.

No, using nicotine in the fasting window before lab work can interfere with blood sugar, fat levels, and even blood pressure readings.