I think the common theme is to make sure you watch your calorie intake and exercise. As an example- I am a 6'6' 49 y/o male requiring 1960 calories a day to maintain my weight. For every 3500 calories in excess of my daily intake I can expect to gain 1 pound of fat. If I wish to LOSE the one pound of fat I put on I will have to create a 3500 calorie deficit.
Lets look at the typical fastfood meal like a double whopper with cheese, fries and a coke.
Double Whopper with cheese = 990 calories.
Large Order of fries = 500 Calories
Large Coke = 310
In one "meal" you have eaten 1800 calories
If I ate a meal like this every day I could only eat another 160 calories all day if I had any hope of maintaining weight.
It is Soooooo easy putting it on, let me tell you about taking it off. I have to walk an hour a day just to burn 500 calories. I have to walk an hour a day every day of the week in order to burn the required 3500 calories to lose one pound.
Right now I have a "calorie bank" of 157,500 calories. (45lbs) I will have to keep my calorie intake below 1960 calories and walk 315 hours in order to get back to where I should be.