gymeejet:
Do you measure the caloric value of your faeces or urine?
You need to take into account energy going out of the body too if you want to stick to your Calorie is a Calorie routine. I excrete ketones - lots of them - in my breath and urine. Therefore I am getting rid of unused chemical energy.

Anyway your calculation is wrong. 4 kcal went to the supporting processes for production of the ketone. This ketone has more than 4kcal of energy though - it has the energy of the fatty acid residues that go to make it up. The 4 kcal that got used to MAKE the ketone are lost to the body - can't be reclaimed!