As Ayn Rand used to say, "Check your premises." Not all calories are created equal. See The Schwarzbein Principle for a clear explanation of this. Food calories are measured in the lab by breaking the food down to its elements and observing how much it heats water. But the body is not a lab. Fat is not broken all the way down to its elements. It's broken down only so far as necessary to use the material to rebuild cells and tissues. Not so for carbs. They are either expended as energy or stored as fat (thanks to the resulting insulin) around the midsection.

Sheldon