Lipolysis

Lipolysis breaks triglycerides into fatty acids and glycerol so the fatty acids can enter the bloodstream. Released fatty acids can travel to working muscles, where they are oxidized for fuel. The metabolic switch from glucose to fat as the primary fuel occurs when glycogen stores in the liver are depleted and adipose lipolysis accelerates. Norepinephrine initiates lipolysis by activating protein kinase A, which recruits HSL and ATGL to the lipid droplet inside fat cells. Noradrenaline and cyclic AMP activate hormone-sensitive lipase at the start of walking. Measurable, substantial fat mobilization accelerates dramatically in the 12–16 hour fasting window. Research shows a selective regional increase in adipose tissue norepinephrine spillover during extended fasting, indicating the sympathetic nervous system plays a larger role in fat mobilization than previously understood. Stopping too early may trigger fatty acid release without completing muscle burning of that fat.