The human body uses stored carbohydrates as an energy source during high-intensity activities and relies on fat for energy sources during low-intensity activities. However, with a high-fat and low-carbohydrate diet, endurance athletes can adapt their bodies to use fat even during high-intensity exercise. One of the benefits of fat adaptation is improved endurance in athletes as they save stored carbohydrates that can sustain longer. Moreover, fat adaptation helps athletes maintain a healthy body weight. Metabolism of fat produces acetoacetate, β-hydroxybutyrate, and acetone ketone bodies. Thus, fat adaptation in athletes can be monitored by measuring ketone concentration in the body through a blood test. The ketone estimation is important to monitor fat adaptation, as individual response to a ketogenic diet is highly variable and needs regular adjustment in dietary strategy.