increased exercise intensity:
think of it this way- you workout and eat at a set calorie level, and you do not lose weight! Now you up the intensity of your workouts, and eat at the same calorie level as before, but now you lose weight. Basically you are creating your caloric deficit via exercise!
and i voted for carb cycling (closet to what I actually do-calorie cycling) even do I do a mixture of if and cc, it makes those low calorie days easier to deal with!