There are a lot of theories of how to lose weight quickly, but I can only account for those I know personally have worked for some people. The first step is not to each as much as you ate before, after all this is how you probably gained weight. Cut back noticeably at each meal, but do not starve yourself. Not eating will not eat away at your fat, but instead will take away from muscle and more useful parts of your body. These suggestions will work, how quickly you define quickly is another question.
Cut out your snacks, except for granola bars and foods similar to that. That is a step in losing weight rapidly. There are those who eat the same food for days on end. If you go for this method, make sure it is something you love. If you enjoy pizza eat a couple of slice a day for two or three weeks, the weight should be coming off.
Basically, you should be eating food with roughage and fiber. I would suggest for some, if they like beans and rice, that would be an excellent choice for you. After all beans will not leave your body collecting waste in your intestines. Depending upon your work schedule, a large diet of corn will most assuredly clean out your intestines. There are varieties, from sweet corn to corn on the cob, this will not leave any excess waste in your body contributing to your weight. Let's face it, most of your weight gain is food that remains in you long past the time it should have been eliminated.
Do not skip breakfast, that will make you hungry during the day. A very important component of losing weight quickly is not to eat past 5:00 PM or thereabouts. Food will not burn up by sleeping. Do exercise whenever possible, bicycling being the easiest to get into the routine of doing many times per week, and will not cost you an arm and a leg. Walk instead of parking next to the stores, or if possible walk the whole way there and back.
Other than eating the same foods all the time, which is only for certain people, follow all the suggestions above as much as possible and all within the same time frame and you will shed pounds quickly.
