Yes, but we measure calories by burning food items in oxygen in calorimeters. Burning fat gives X amount of heat, burning fiber gives Y amount of heat. Fat and

Yes, but we measure calories by burning food items in oxygen in calorimeters. Burning fat gives X amount of heat, burning fiber gives Y amount of heat. Fat and fiber both have calories when you burn them in a furnace. But body does not use fiber for calories, you won't get fat on fiber. That is the distinction between dirty and clean calories, not everything burnable will be usable for energy in body and not everything that body actually digests will be stored in fat tissue.