I feel like I reasonably addressed the basic issue. I don’t think someone can gain literal weight without eating more calories than they consume, because that is how thermodynamics work. But it’s not always as straightforward as over eating, and it doesn’t always feel like over eating. For example, common cases of obesity in the US are due to a high amount of hyper processed foods that are calorie dense but don’t feel filling. Fat people don’t gorge themselves every meal, they eat what feels like a regular amount to sate their hunger. That’s why semaglutides are so effective, they make you feel hungry less and full faster. And shame based approaches at making people eat less have been proven not to work, because they don’t teach them to choose better foods or make them feel less hungry.