How weight loss surgery works is simple. The bariatric Surgery alters your digestive system (stomach and / or small intestine) to make it impossible for you to eat much food at one sitting without suffering unpleasant side effects such as dumping syndrome. This digestive side effect acts as a brake on calorie intake, and typically leads to significant loss of weight in the 2 years after surgery. There are three types of procedures of Bariatric Surgery - 1. Restrictive 2. Malabsorbtive 3. Combined.