Gastric sleeve surgery removes roughly 75–80% of the stomach, leaving a narrow tube. The result is that a much smaller volume of food makes you full, and — because the removed portion produces most of the body's ghrelin — you feel considerably less hunger, at least at first.

Both of those change how many calories you take in. What follows is what that usually looks like, and why the numbers move over the first year.

If the scale has started moving the wrong way after your sleeve, you have probably found the "pouch reset" — a five-day return to liquids and then soft foods, sold as a way to shrink your stomach back down.

Here is the honest answer: the reset does not shrink your stomach, because that is not what went wrong. What it can do is interrupt habits, and that is worth something — just not what it's usually advertised as.