In general, you will lose about 50 percent of your excess weight during the first six months after gastric bypass surgery. Expect to lose another 25 percent in the second six months. In contrast, gastric banding results in an average of 25 percent loss during the first six months after surgery, with an additional 15 to 20 percent in the next six. 

Prior to surgery, you should prepare to change your eating habits. After surgery you’ll need to drink small amounts of fluids throughout the day to avoid dehydration. Stay away from carbonated beverages, which can expand your new, small stomach and lead to discomfort. 

As weight is lost, the need for many medications often disappears. It may also be difficult to ingest large pills, so other forms of medications may be prescribed, such as liquid, suppository or a patch that can be applied to the skin. During the first year after gastric bypass, failure to take prescribed vitamins and minerals can lead to malnutrition, a low red blood count (anemia) and weakened bones. During any period of calorie restriction there is an increased risk of gall stones—work with your primary physician to take the appropriate precautions. 

Each patient will experience changes in body shape after surgery. How your body changes depends on your body type, age and skin elasticity. Support groups and frequent post-surgery visits can be critical in helping you adjust to these changes and also get your questions answered. Be open with family and friends—they can provide better support if they are aware of the new nutritional and lifestyle changes that you’ve made.