Weight gain and weight loss all comes down to a simple equation. Energy in vs energy out.

Don't make the mistake many people make of setting your self up for failure and self-fullfilling prophecy.
If you don't want to be fat, don't be. It WILL require work, diligence, but it is your decision - and you can start now with some positive NLP.

Everytime you tell yourself you are going to get fat, tell yourself 6 times, out loud, you will not be fat, you will be healthy and are capable of being whatever you want to be, you will not be fat.
So for every single negative thought in your head, counter it with a postive affirmation out loud, so you can hear it, and repeat it.

Baby or bo baby, you will be fat if you let yourself be.