Energy balance

Fat loss magnitude is determined exclusively by the size of the energy deficit, regardless of whether that deficit is created through dietary restriction alone or a combination of diet and aerobic exercise.

To lose fat, you must create a caloric deficit. Whether you achieve this deficit by eating less, moving more, or a combination of both, the amount of fat you lose will be determined by the size of that deficit, not the method used. If you match the deficit, diet-only and diet-plus-exercise yield equivalent fat loss, though exercise improves fitness.