If you triple your cardio to like an hour a day, you'll knock off a lot of weight in no time. 20 min ain't gonna do squat. Just make a decision to move 4-5 miles a day on foot. I was 210 in Jan of last year. Got acrivated with my reserve unit and by June I was 180, lean and aerobically fit. I fell out of a run in Jan of last year, bucked up and started run/ walking as best I could every other day I wasn't PT'ing with my platoon. I soon made 4-5 miles at a run the whole time. Then I added my pack, and lost more weight.
20 minutes barely gets you up to your target heart rate if you are pushing yourself hard enough. You are barely getting to the point where you body turns to the fat stores for energy in 20 minutes. Some consider walking for 20 min on a treadmill for 20 minutes "cardio."
Hell, get a cab, or have a frfiend drop you off four miles from your home, that way there's no turning back early or losing the urge to continue. The only thing that will get you home is your two feet.
Push yourself HARD. If you are not, you won't get much out of your exercise.
I did that Atkins diet, lost 14 lbs. in two weeks, no carbs at all. But I put it right back on when I stopped. I found I wasn't so much carb dependant as activity poor. Do a lot of moving every day. That's all I did and I knocked off thirty pounds.