How does the band work?

Gastric Band is a variation of gastroplasty in which the stomach is neither opened nor stapled. The band creates an hourglass shaped stomach having a small upper pouch with a narrow outlet. The new small upper gastric pouch restricts the amount of food stomach can hold and that can be consumed at one time. So one feels full and satisfied after a small meal. The narrowed outlet increases the time it takes for the stomach to empty. One therefore feels full for a longer time with no desire to eat. The subsequent reduction in food intake results in weight loss. The Flash Video explains how the Lap-Band system works:
Lap-Band Adjustment Video