They studies show that the more weight a person loses, the stronger appetite becomes until it counteracts all the hard work they've done to lose it in the first place.
The body regulates weight by trying to maintain an equilibrium between the calories we eat and the calories we burn. When we expend or cut calories, and start burning our stored energy, appetite kicks in to tell us to eat more. Hall's studies have shown that the more weight a person loses, the stronger appetite becomes until it counteracts, and sometimes completely undoes, all the hard work they've done to lose in the first place.
Hall's model predicted that in order to achieve the weight loss reported in that study, people whose diets started at 2,500 calories per day had to cut just over 800 calories a day. Their bodies responded by prompting them to add to their daily caloric intake an estimated 83 calories for every kilogram of weight they lost.
Dr. Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center, previously told CNN this feedback mechanism is why weight loss gets harder the more you lose. But crucially, the drugs didn't merely have an effect on the number of calories people cut from their diets. They also lowered the number of calories their bodies were prompting them to eat back as they lost weight - in effect, weakening their appetites. For Wegovy, people only wanted to eat back about 49 calories daily for every kilogram of weight they lost. For Zepbound, that number was 48.
While it may stymie dieters, the appetite feedback circuit is actually a good thing, he said. It would be dangerous if a drug or treatment got rid of appetite entirely. If that happened, a person might stop eating entirely until they died.For example, one theory has been that weight loss damages metabolism, so people end up burning far fewer calories at rest than when they started and can regain weight very easily.