Short answer: **yes, but it depends on why you’re fasting.** If you’re fasting for a strict metabolic fast, then a protein shake breaks it. If you’re fasting mainly for calorie control or habit building, a shake might still fit your goals—just understand the trade‑off. ## When a protein shake breaks your fast A protein shake has calories and amino acids, which means: - insulin rises - digestion starts - the “fasted” state ends So if your goal is a strict fast, a shake is a no