During fasting, insulin levels _______________ while glucagon levels ___________.

During fasting, the body's energy needs shift due to the lack of food intake. Insulin is a hormone that promotes the storage of nutrients, particularly glucose, by facilitating its uptake into cells. When fasting occurs, the availability of carbohydrates from food diminishes significantly, which leads to a decrease in insulin levels.

On the other hand, glucagon is a hormone that has the opposite effect of insulin. It stimulates the liver to release stored glucose into the bloodstream, which is crucial for maintaining blood sugar levels during periods without food. As fasting continues, the body responds by increasing the production and release of glucagon to ensure that energy remains available from glycogen stores and to promote gluconeogenesis, the formation of glucose from non-carbohydrate sources.

Thus, during fasting, the decrease in insulin allows for the mobilization of energy stores, while the increase in glucagon supports maintaining glucose availability for bodily functions. This hormonal balance is critical for metabolic homeostasis during times of energy scarcity.