What is good for one person is not good for another. That is the basics of nutritional differences. These plans and kits that claim to help you lose 10lbs in 3 weeks are often the same information regurgitated from the mouths of thousands of spokespeople.
Simple fact of the matter is, you must exercise and eat right to lose weight. While everyone has said this to some degree, the thing most overlook is nutrition. Just because someone cuts out 300 calories doesn't mean anything if what they cut out was food that was good for them. For example, 1 Hershey's candy bar, which is about 2 inches by 6 inches, has 210 calories. It is also high in sugar and fat. Compare that to a salad made of iceberg lettuce, grape tomatoes, broccoli, and Italian dressing. 1-cup lettuce, 1/2cup chopped grape tomatoes, 1-cup broccoli, and 2 tbsps Italian Dressing has 150 calories, which is 60 less than the chocolate, minus most of the sugar and fat, plus you get a lot more.
The problem is, however, that most people think vegetables are disgusting. While I detest celery, myself, I have learned to eat it, because it is healthier than junk food. Most people, in the United States especially, do not care if something is healthy. They only care if it tastes good. For the longest time, I avoided any salad dressing that was not ranch. Hated the fact that the others might be different. Recently, I learned that my father has diabetes, as does my grandfather, my aunt and uncle, and some of my cousins. So, I decided to make changes in my life.
Long story short, 2 weeks ago today, I weighed 215lbs, and today, I am down to 202.4. In order to lose weight, you must change your life, but in order to make the changes, you have to first want to change. And you have to do it gradually, step by step. Instead of chugging Mountain Dew, grab some flavored water, or just plain water instead. Do this for 10 days, and then see what else you can change. Who knows? You might amaze yourself.
Sorry if that sounded a bit pitchy at the end, but that is my own personal experience.