during the first few days of a fast, what energy source provides about 90% of the glucose needed to fuel the body? triglycerides protein ketones glycerol glycogen

Protein is the energy source provides about 90% of the glucose needed to fuel the body during the first few days of a fast. During short periods of energy abstinence, the human body burns primarily free fatty acids from body fats stores, along with small amounts of muscle tissue to provide required glucose for the brain. After prolonged periods of starvation, the body uses the proteins within muscle tissue as a fuel source.