Gastric bypass is a series of steps initiated starting with decision to undergo procedure. Identifying existing nutritional deficiencies is first step towards surgery. Vitamin and mineral deficiency often occur in obesity, and need to be addressed before procedure. The surgery itself has two goals; to reduce volume of stomach and shorten food transit time in intestine. After surgery stomach cannot receive large meals or participate in digestion. This by itself limits food intake. Food also bypasses a large part of intestine and has little time to interact with liver and pancreatic enzymes. As a result, nutrition absorbed from diet drops drastically. In most types of gastric bypass surgeries done today only 50 cm of intestine is allowed to function in normal fashion. Compare this to food absorption taking over 7 feet of small and large intestine before surgery.

With such a radical reduction in capacity to assimilate food, postoperative period can be rather tricky. Only clear fluids are advised for first two days while waiting for gut to recover. The gut is then re-trained for about two months before it can go back to a normal diet. During recovery period limitations imposed by gastric bypass procedure should be kept in mind. After surgery stomach has become much smaller and can only hold approximately eight ounces at a time. The stomach has also lost its ability to pulverize food to initiate digestion. Consequently appropriate diet for postoperative recovery would be a liquid to soft solid diet that can be taken six to eight times a day in small quantities. Nutrient fluids are preferable since they can provide hydration and energy at same time. Non-nutrient fluids are best avoided or at least restricted to in-between meals.