Thinking that you can just "whoosh" away fat cellsis an oversimplified (and inaccurate) way of looking at weight loss that doesn't tell us anything about how the body really regulates weight. While most people have a calories in, calories out view on weight loss , many people don't realize that the brain is what controls weight and weight regulation, Dr. Stanford says. "When weight loss occurs, the brain really tries to do what it can to compensate, such that it's going to try to rebound back to where it was before the diet," she says. That's why so many people go through " weight cycling ," or repeated loss and gain of weight, for instance. "The body doesn't recognize that excess that's not needed, so it'll do whatever it can do todefend that," she says. In other words: People experience weight-loss "plateaus" because their bodies are designed to work that way, not for lack of willpower.