Ketosis is a metabolic state in which your blood contains high levels of ketones, specifically beta-hydroxybutyrate. It occurs when your body begins to use fat as its primary fuel source due to a lack of access to glucose, or blood sugar.
Many cells in the body prefer using glucose for fuel. But when your body doesn’t have enough glucose to power these cells the body releases fatty acids from body fat stores in large amounts. Resulting in less body fat as the body converts fat stores into energy.