What is the purpose of fat and glycogen?

Answer 1

Both are stored forms of energy in the body. Glycogen is stored glucose in the form of carbohydrate which is stored in the liver and muscle.....a reserve of glucose that is readily accessible when energy needs exceed the amount of free glucose in the blood. This glycogen can store about another 2000 calories, or about 6 hours worth. Fat is the most energy dense form of energy storage in the body and therefore can provide a longer reserve if fasting conditions. In that setting, however, when the glycogen is depleted, the body must begin to break down both fat and actual muscle fiber. The reason for that is because the brain is a huge consumer of energy, and a third of that energy for the brain must come in the form of glucose itself. Fat can be broken down into shorter fatty acids chains which most of the body can use, but it cannot be converted to glucose itself. Muscle fiber, however, can be and must be, for the brain to continue proper function. Both glycogen and fat are substrate the body uses to maintain function, cell integrity, repair and enough energy to power the major organs during periods when food is unavailable...a situation that was common when we were still hunter-gatherers and time between meals was uncertain.