Gymee, I never meant that energy is destroyed. The basic laws of physics say energy can be neither created nor destroyed. Here is what I was saying in a nutshell: Fat provides 9 kcal/g. But, in order to convert that Fat to Ketones [which your body can use,] your body has to expend 4 kcal worth of energy. Think of it as a 4 kcal boost in your Metabolism.

You can put the 4 kcal on the expenditure side if that helps. For each gram of fat your body uses, it must expend 4 kcal of energy. This energy is lost [from the body] in the exact same manner as if it had been expended through your Metabolism or by Exercise.

Think of it like this: Calories in - Calories out = Net Calories. The problem is we are not counting all the Calories out. We need to include those Calories expended breaking fat down into Ketones, those expended breaking Protein down into Glucose, and those Calories that are locked up in body tissues such as muscle. If you count these calories as Calories out, then you will see that eating fat increases the Calories out, thus reducing the Net Calories. Not only that, Fat and Protein provide more satiation, possibly reducing the Calories in.

On top of all this, if you do not have insulin to store the excess calories as fat, they are broken down [in the case of fat] and permenantly excreted from the body. Therefore, a low-carb/hi-fat diet works by dramatically increasing Caloric expenditure. It's still calories in/calories out. Nutritionists don't seem to grasp the idea that Calories can be expended by means other than exercise.