It depends on how long you've been at your current weight. The human body tends to get comfortable with it's weight after a couple of years and doesn't want to change. So, while you can bust your *** to get the pounds off, as soon as you stop busting your *** your body is going to try to go right back to where it was before.
This is the reason weight loss needs to be a complete lifestyle change, not simply a diet you follow for a month or two. It's something that needs to be approached in moderation, with a goal of losing no more than a pound or two a week, because your body needs to be taught to tap the fat stores without the added stress of a crash diet (such as fasting) or insane workout schedule.
While it is possible to trick your body into shedding 30 pounds in a week, it's your body responding to the "holy ****" factor of what you are doing to it. It's tapping the fat stores (and muscle as well, especially if you're fasting) to respond to the self-inflicted crisis and keep you on your feet until it can adapt to what you are doing to it. Once it adapts, it'll take steps to put itself right back at your old weight (or put you in the hospital, if it can't adapt).
The trick is to accept the fact that if you want to drop 50 pounds, expect it to take 25-50 weeks if you want your body to stay healthy while doing so (and have a better chance of keeping it off). Figure out your metabolic statistics (Web MD has a good calculator to use), and be honest with the input. For example, I'm 5'8", 34 years old, and 200 pounds, working out five days a week (moderate activity level). According to the calculator, I burn 2828 calories a day, meaning I need to consume that many to maintain my current weight level.
Plug your information in (don't lie about the activity level, either) and see the results. Then reduce your daily calorie intake by no more than 500 calories from that number. Without increasing your activity level, that will result in a calorie deficit of 3500 calories a week, which is equal to one pound of body fat.
However, as you lose the weight, you need to re-calculate your metabolic rate to match your current weight. Using my example above, if I dropped 10 pounds my rate drops to 2757, and I need to adjust my intake accordingly in order to maintain the weight loss.
And once you do reach your goals, don't EVER go back to your old eating habits. Sure, have a pizza once in a while; life isn't worth living without it. Just keep in mind that "once in a while" doesn't mean "twice a week."
Hope this helps. Good luck!