For example, 500 calories of oat biscuits compared to 500 calories of plain oats?
“Calories are calories” is the dumbest oversimplified answer to this question.
Higher glycemic index carbs, refined carbs, drastically impair insulin sensitivity, which can cause greater weight gain with the same calories. Refined carbs also contribute to non-alcoholic fatty liver disease, which can result in visceral fat gain.
More refined carbs also generally contain less fiber. Fiber is important for keeping a healthy gut microbiome, which is scientifically proven to be important for managing many metabolic hormones that in turn regulate metabolism and weight gain.
There is a reason that cultures eating lots of legumes and brown rice aren’t getting as fat as Americans eating sugary 3d-printed white bread and refined pasta and instant oatmeal.
1 calorie = 1 calorie, but that does not mean that 500 calories of one food is equivalent in health to 500 calories in another food. There are still going be differences in volume, satiety, nutrient density, etc.
No, calories are calories. If you ate pizza every day but you made sure you were eating under your caloric needs, you would lose weight. But you would probably be hungrier and have less energy than if you were eating whole foods. Mainly because the fiber from plant foods and the protein from lean meats would help you feel full for longer. If you were eating 500cal of oatmeal, you will definitely feel full. Oats have a lot of fiber and digest more slowly. On the other hand, oat biscuits probably have a lot of added sugar which will digest very quickly and an hour or two later, you’ll feel hungry again. But this is the main concept behind tracking macros. You can eat whatever you want as long as you don’t go over your calories.
Edit: to add that it is also much easier to overeat simple carbs. I find oatmeal to be very fulfilling, and I can only eat so much before I start to feel full. But I can eat a lot of Oreos in one sitting without realizing I just stuffed myself with 500 calories.