What happens to your body hour by hour when you fast
A science-backed, hour-by-hour breakdown of what your body does during intermittent fasting — from glucose to fat-burning to autophagy.
When you stop eating, your body moves through a predictable sequence of metabolic states. In the first few hours, insulin falls and your cells begin burning through stored glucose. By around hour 12–16, fat becomes your primary fuel source — and if you push further, autophagy, your body's cellular repair process, begins in earnest. In the first one to two hours after your last meal, your body is still digesting and absorbing nutrients. Blood glucose is elevated, insulin is high,…
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