The body turns the food you eat into glucose. Glucose is the body's primary source of energy. When you eat a large amount of food, the glucose levels increase rapidly. Afterward, the pancreas releases insulin that moves glucose to the cells for use when the bloodstream is inundated with it.
When the body has increased glucose levels, the pancreas is likely to produce too much insulin, and this can lead to a low blood sugar level. The effect of this is that the brain thinks you need more glucose and makes you feel hungry again.
Cycling between low and high blood sugar can lead to weight gain. But by eating frequent, small meals, glucose and insulin levels will be more stable.