where does body get energy from when fasting
Starvation response Starvation mode is a state in which the body responds to prolonged periods of low energy intake. During short periods of energy abstinence, the human body burns primarily free fatty acids from body fat stores, along with small amounts of muscle tissue to provide required glucose for the brain. After prolonged periods of starvation the body has depleted its body fat and begins to burn primarily lean tissue and muscle as a fuel source.
Carbohydrate loading Carbohydrate loading is generally recommended for endurance events lasting longer than 90 minutes.[3] Many endurance athletes prefer foods with low glycemic indices for carbo-loading due to their minimal effect on serum glucose levels. Low glycemic foods commonly include fruits, vegetables, whole wheat pasta, and grains. Many marathoners and triathlon participants have large pasta dinners the night before the race. Since muscles also use amino acids extensively when functioning within aerobic limits, meals should also include adequate protein.[4] Large portions before a race can, however, decrease race-day performance if the digestive system has not had the time to process the food regimen.