All diets work because you are eating less calories. If you lost 30 lbs, its because you ate less calories. You may not have consciously realized it while you were doing it, but you did.
The key to success as I see it, when fat loss is the goal, is to find a way to cut calories as necessary without making it uncomfortable. If you can do that, you're golden. Personally, when I'm really focused and want to lose, I'll go for foods that are low in calories but fill me up.
Earlier this year when I wanted to drop 10 lbs, I did it that way. I went with mostly meat and A LOT of vegetables. I added a little bit of fats from cheese and mayonaise, and allowed reasonable cheat days once per week. It worked.
I balance it out by not doing that all the time.