Tight at beginning. The ideal gastric sleeve should be fairly tight at the beginning (usually a 34 fr bougie), should begin about 1 inch from the pylorus (the end of stomach), and go directly to the angle of his right next to the esophagus. Experience shows that the sleeve will not stretch more than about 5% if kept tight from the beginning.
Eat small amounts. The best way to keep your stomach from stretching after a bariatric surgery is to make sure you keep strictly to the amount of food that you are told to eat by the surgeon. Often that amount is 1/2 cup of food at a time. This is a small volume of food and sometimes hard to keep track of, but eating larger volumes is dangerous and can stretch your stomach or remaining pouch.
Eat properly. Eat very small meals very often throughout the day. Your dietitian will counsel you on this. Small frequent meals will help to keep the stomach small.