I think this is ignoring the fundamental issues with weight and health. Each day you naturally burn a set amount of calories dependent upon a number of factors

I think this is ignoring the fundamental issues with weight and health. Each day you naturally burn a set amount of calories dependent upon a number of factors - largest being your activity level and your current weight. If you go over what your body burns, you will gain weight. If you stay under it, you will lose weight. It's that simple. Of course nutrition is critical in this. You need a set amount of vitamins, proteins/amino acids, and so on, to keep your body functioning optimally. Eating a cookie provides basically nothing in terms of nutrition and sends your a pretty good chunk of the way towards your daily 'limit' of consumption. So it means if you eat a cookie you're going to need to be that much more nutritionally conscious on a smaller limit of max calories, to remain healthy. Paradoxically, this is even more true for fit individuals than fat. Even when you're doing nothing, your body is constantly burning calories to keep things going. Fat individual's bodies have to work far harder during this process, and so they passively burn far more calories than fit individuals. This is why an obese person could, in general, start losing weight by "just" eating 3000 calories a day. By contrast, eating 3000 calories a day would see a fit person's weight start rapidly increasing. So a fit person has a far smaller limit to squeeze in all their nutrients. It leads to the paradoxical outcome that that cookie is relatively worse for you if you're fit than if you're fat!