During a 24-36 hour fast, growth hormone rises dramatically, adrenaline (norepinephrine) elevates, and metabolic rate increases—the opposite of what most people expect. Research shows metabolic rate may rise up to ~14% during short-term fasting.
This companion explores the growth hormone surge and muscle protection, the norepinephrine increase and alertness, why metabolic rate rises, how fasting differs from restriction, and what you experience during the hours of a fast. (4 min read)