When blood sugar levels are high, as they would be after consuming a carbohydrate-rich meal, insulin levels would increase. The hormone insulin helps to convert excess glucose to glycogen, also known as animal starch. Glycogen can be stored in the liver until such time as it is needed. Insulin also helps transport glucose from the blood to the body cells to be used in respiration. After twelve hours without eating, glucagon levels will increase. The body needs energy and must have glucose in order to carry out respiration. Therefore, the hormone glucagon will be released and it causes glycogen to be converted back to glucose once again. This glucose can be transported via the circulating blood to the cells of the body to be used in cellular respiration to produce ATP, the cell's fuel source. The hormones insulin and glucagon help maintain homeostasis in the body regarding glucose levels.