Adrenaline (epinephrine) increases during fasting. Research by Zauner found that resting energy expenditure actually increased during short-term fasting due to elevated norepinephrine. This is your body’s way of mobilizing energy stores—signaling fat cells to release fatty acids and keeping you alert to find food. Rather than making you tired, fasting often produces heightened alertness and stable energy.
This companion covers the counter-intuitive reality of fasting energy, what happens hormonally during fasting, the evolutionary logic, the experience many report, and the metabolic effect on lipolysis and thermogenesis. (4 min read)