Calorie meter

It Takes 3500 Calories To make A Pound Of Fat!

So, as long as you're active, and burning of calories, calories shouldn't have too much of a chance to turn into fat.
You burn more calories when sleeping than watching television.

Then how many calories do you need a day?

The calorie requirement differs with your age and sex.

Age:                                    Male                                             female

 1 to 3 yrs                           1300Kal                                       1300Ca

 4 to 6 yrs                            1700 cal                                      1700 cal

 7 to  10 yrs                         2400 cal                                       2400 ca

 11 to 14 yrs                        2700 cal                                       2200 cal

 15 to 18 yrs                        2800 cal                                       2100 cal

 19 to 22 yrs                        2900 cal                                       2100 cal

 23 to 50 yrs                        2700 cal                                       2000 cal

 11 to 14 yrs                        2400 cal                                       1800 cal

So think before you are feasting and fasting.
Keeping away from fast foods will let you strain yourself 30% less