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.
Insulin will prevent glucose levels from increasing to a point that is too high, while glucagon prevents it from dropping too low. Glucagon production is stimulated when an individual eats a protein-rich meal, experiences a surge in adrenaline, or has a low blood sugar event.