Right. It seems like the issue is that "calorie in/out" means different things to different people. For some people it refers to the simple fact that humans are

Right. It seems like the issue is that "calorie in/out" means different things to different people. For some people it refers to the simple fact that humans are subject to the laws of thermodynamics. For people trying to lose weight, it refers to diets which are structured around counting your calories. It's hard to doubt that lowering your calories consumed will cause weight loss. However, it's not obvious that the physical mechanism behind weight loss in itself provides enough structure for people to use as a practical tool for weight loss. It's like if someone is trying to pitch a faster baseball and their coach introduces them to the "conservation of momentum" strategy for throwing faster. The idea being that if you want to move the ball faster, you have to move your arm faster too. Well, duh, but it's not obvious whether this will help anybody. It might be the case that practical strategies for pitching faster never make reference to the principle of conservation of momentum. That doesn't mean that conservation of momentum doesn't ultimately explain why every different strategy works, but it doesn't make "conservation of momentum" a strategy all by itself. "Eat high quality foods" may very well be a better strategy for losing weight than counting your calories. It might be easier and more healthy than calorie counting for most people. That doesn't mean that "calorie in/out" doesn't on some level explain why this strategy works (although, there might be good reason to doubt this in some cases, new research suggests that the interaction between gut bacteria and food are an important factor in how people respond to different diets). But the fact that "calorie in/out" explains weight loss doesn't mean that it needs to be the central concept in everybody's dieting decisions.