No, sucking your belly in does not work...believe me xD
First I want to share something about me. I'm not skinny, and I'm also not fat, I fall in the O.K. category. I am 5' 8.5" tall which is normal where I live xD and my weight is around 156 pounds, so my Body Mass Index is 23.4 which is normal weight. The thing about me is that I gain weight VERY, and I mean VERY easily. So whenever I start gaining weight I use the following method to get back to normal. I accomplish this in 1-2 weeks.
Then, read the following!
Number One: Water! Drink a lot of water, specially before eating and after eating, believe me, this will make you eat a lot less if you are used to eat a lot. For some people this simple method works wonderfully and it's all there is to lose weight. For some others it doesn't work alone.
Number Two: Eat everything using only forks, knives and spoons. With this I mean that you must not eat side food like bread, nachos, tortillas! You can eat all the food you want if the food is not from restaurants or fast food services, so if the dish is made at home, you can eat until you are full! BUT REMEMBER only use a fork, knife or spoon!
Number Three: The hard one...you must stop eating junk food. Come on, I know you can do it for 2 weeks! and also you will save money *blink xD
Special: Using the three methods as explained you will lose fat really fast, you just need to commit to do it! is not that hard, I mean, it's only 2 weeks. Now, if you just can't drink a lot of water, and you want to eat at fast food restaurants then you can erase step one, and change step 2 for this: eat everything normally and in the way you use to BUT, only eat half of it. Yes, you can eat anything you want, in the way you want, but only half the normal amount you would eat. This method is slower but it also works!
You want an estimate of weight loss/time? Well, for me it is like this:
Normal method (the 3 steps): 4 Kg. (8-9 pounds) per week.
What do you think? Just remember, this is what happens TO ME, I can't tell you what would happen to you people, but the fact that you will lose weight...yes, YOU WILL!
Thank you for reading and I really hope you can accomplish what you want! This works excellent if you have some extra pounds and you have to go to the beach in a couple of weeks xD Take good care and be happy!!!
Link to calculate your Body Mass Index: http://www.nhlbisupport.com/bmi/