'Clean' and 'dirty' calories is a myth if we're only talking about weight
Fitness culture likes to split food into 'clean' (healthy) and 'dirty' (processed, bad), implying that 'dirty' calories somehow harm your physique more than an equal number of 'clean' ones. From a pure energy-balance standpoint for gaining or losing weight, that split has no physiological basis: a 500-calorie surplus from vegetables and a 500-calorie surplus from fast food both lead to weight gain the same way, because the body primarily counts total energy, not the 'moral category' of its source.
That doesn't mean the source of calories doesn't matter at all — it just matters for a different reason. Processed foods usually contain less fiber, fewer micronutrients, and less protein per calorie, which makes them less filling than the same calories from whole food, and in practice that often leads to overeating. Diet composition also directly affects health independent of weight — vitamins, minerals, and the inflammatory profile of food matter in their own right, not just as a line item in a calorie count.
Practical takeaway: sorting food into 'clean' and 'dirty' for weight control purposes isn't quite accurate — it's more precise to say some foods help control appetite and health better than others at the same calorie count, rather than there being some magical difference in how the body 'processes' calories based on their origin.