How does calories make us gain/lose weight?

                                       

        3500 calories = 1 pound [of fat] gained

       

  Likewise, 3500 burned calories = 1 pound of weight loss.

  

This applies no matter who, what, when, where, how....or why!

If I ate 3500 calories today and 3500 more calories tomorrow...

and did nothing at all to burn calories, then I will have gained 2 pounds of fat (If 3500 calories = 1 pound, then 7000 calories = 2 pounds). 

Whether the pound(s) gained are fat pounds or muscle pounds depends on the food that was eaten from the start (i.e. nutritious food or non nutritious food).

On the flip side...

3500 burned calories = 1 pound of weight loss. 7000 burned calories = 2 pounds of weight loss. Basically, follow the theory that when that 3500 calories settle, then a pound is gained. 

What stops calories from settling? 

Use of calories as energy stops calories from settling/accumulating to that 3500 = 1 pound mark. Things that burn calories (use energy) are:

walking   running    thinking    talking    working out    sports   reading   playing

and many many more things similar