I was wondering, why do we say that we ‘burn’ calories. And then I came to this question.
Yes, if you were burning food that provided you exactly the caloric intake you need to maintain your weight, and if you ate only that and didn't replace the lost calories by adding additional food. To carry it to extremes, you could oxidize your food to an inorganic ash. Metabolic (food) calories are ultimately identical to the energy found in any non-food fuel. They're just found in molecules that are digestible. But you'd also be destroying vitamins, fiber, etc., as well as flavor. Slightly singeing it would destroy a few calories, maybe, of properly cooked food.