Can i drink coffee while fasting? The metabolic rules you need to know
Dr. Susan Carter, MD: Endocrinologist & Longevity Expert
Nov 30, 2025 · 9 min read
Black coffee generally keeps a metabolic fast intact because it has about 2–5 calories per cup and does not trigger a significant insulin response, so fat burning can continue. The nuance is caffeine’s effect on cortisol and your goal (weight loss vs. strict “autophagy” rules), which can change what “allowed” really means. “From a hormonal ...