What can you do to not shrink down to nothing after having a weight loss surgery?

Normal size: The weight loss surgery is designed to assist patients to lose weight loss who have been unable to decrease their weight any other way. After the surgery the patient's will continue to eat, but just in smaller portions. The amount of calories that they take in will be enough for normal life, but the body will be able to mobilize the excess fat stores, hence losing weight.

Excessive wt loss: That usually doesn't happen. Most people just worry about losing enough weight. The only patients I have seen that have 100% of their excess weight are those that became obsessed with working out (an marathon runners). If you have surgery (assuming it was done correctly by an experienced surgeon), and eat a normal amount of food, you will not shrink down to nothing.