Cardio will work wonders until you've depleted your glycogen stores. What happens after that, makes all the difference in the world.
If you continue cardio with a depleted glycogen level, with a sufficient daily intake of calories (food specific), cardio will slowly emulsify bodyfat. However.... If you continue cardio with a depleted glycogen level with a insufficient daily intake of calories, then your body will go into the catabolic state causing metabolism to decrease and fat emulsification to cease. As you can see, the most important factor is calories.
The bottom line: If your not taking in enough calories to support the cardio (or strength training sessions) your headed down a path of failure.