Diet is the wrong word when referring to fad diets. it is a lifestyle change. As stated, caloric intake is key. Also having a "treat" is key, if you don't reward yourself, or partake in a craving, the next time you get it, you can go crazy and over do it. Exercise and healthy eating habits are the core to a successful "diet". If I want to eat something I normally wouldn't, or have a few extra drinks on a night out, I make up for it in the gym. Everything in moderation, cut and dry.
The fad diets might work great, in the short term, but can do more harm then good in the long run. Atkins is dead, and so is the diet really. De- pleating the body of carbs can be very negative to your well being. It makes the body go into ketosis, replacing keloids for fuel, instead of carbs, and can result in high ph in your blood. Sure it burns off the fat reserves you have, but so does starving yourself, and neither is healthy or ideal.