A 72-hour fast pushes your body through intense changes. While it may cause fatigue, hunger, and dizziness early on, it also triggers powerful health responses that many find beneficial.

After about 8 hours without food, your body runs out of digested fuel and begins using stored glucose. Hunger hormones like ghrelin rise, making cravings stronger. By 12 hours, human growth hormone (HGH) is released, helping protect muscle tissue.

As glucose runs low, your body turns to fat for energy. Around 24 to 36 hours, autophagy starts—a “self-cleaning” process where cells break down and recycle damaged parts, improving overall function.

By 48 hours, hunger often fades, and mental clarity improves. At the 72-hour mark, your body reaches a reset point. You can slowly reintroduce food, and many benefits—like fat burning and cell renewal—may continue afterward.

Though some, like Sharon Osbourne, swear by fasting, medical experts advise speaking with a doctor first. Long fasts aren’t safe for everyone and can carry serious health risks.