Glycogen Depletion

The first part of a fast primarily uses glycogen rather than fat. Cutting dietary carbohydrates depletes glycogen stores and releases water that is then excreted. Fluid loss during glycogen depletion carries minerals out of the body. The rapid initial weight loss in the first few days of a ketogenic diet is usually fluid loss, not fat loss. Around hours 12 to 14, lower insulin and higher glucagon begin loosening inhibition of fat release. While glycogen remains available, the body has little incentive to rely heavily on stored fat. Liver glycogen is described as depleting around hour 10 to hour 14 depending on meal composition and activity level.