Do you ever notice how some women can do 6, 9 or even more hours per week of cardio and still have fat to burn, whereas others can spend a few hours a week and it burn the fat, no problem(don't you just hate THEM! - smile!)? I often have women telling me that they actually gained weight doing cardio!
Scientists think they have an answer to this. It appears that some of us are "Compensators" and some are "Non-Compensators". Turns out that cardio makes Compensators hungry. As a result, Compensators end up consuming more calories, all but wiping out their cardio efforts! Non-Compensators, however, do not seem to experience an increase in appetite.
If your cardio program is not working for you, check your post-exercise appetite level and calorie intake to see if you are a Compensator. If you are, you might be better off with a program of high-intensity resistance exercise and interval training!