Fruits and vegetables contain soluble and insoluble fiber in varying proportions. When you eat soluble fiber, it absorbs water to form a gel-like mass, which helps you feel full and provides other health benefits. It prevents a surge in blood sugar after you eat by slowing down the absorption of carbohydrates.
If the blood glucose level falls to dangerous levels (as in very heavy exercise or lack of food for extended periods), the Alpha cells of the pancreas release glucagon, a hormone whose effects on liver cells act to increase blood glucose levels.
The binding of insulin to its receptor on liver cells leads to increased synthesis of glycogen and inhibition of glucose production by liver cells. Over time following a meal, glucose levels will fall, and once a certain threshold is reached, low glucose levels stimulate glucagon release from pancreatic alpha cells.