With seven calories per gram, alcohol has almost the same calorie content as pure fat! Yet alcohol has no nutritional value, and despite its calorific content, may actually make you feel more hungry instead of less, as it lowers your blood sugar.
It has that much calorie content because it's almost fat, in fact. Alcohol dehydrogenase converts alcohol in acetaldehyde, which is then converted into Acetyl-Coenzyme A. That's one of the crossroads of the energy metabolism, and what fat is broken down to when it's being used by the cell. So it's only a few oxydation steps removed from pure fat, and still retains a lot of energy potential.
The reason why it lowers blood sugar and, in general, makes you fat, is the way our body regulates itself. The body can be a bit stupid sometimes. Anyway, what happens when you're drinking alcohol is that the liver gets swamped with Acetyl-Coenzyme A. Many of the energy metabolism enzymes are regulated by this one molecule. It's fairly logical, if you have a lot of it kicking about it means you have a lot of energy, so you don't have to burn any more fat or sugar, you need to hold off there until the present Acetyl-Coenzyme A is used up.
But you keep accumulating it. And more, and more! Where's it coming from? No matter, the body does the sensible thing at that point.
"Hey, we've swamped in this stuff, we obviously have too much energy! Time to store up some."
And store it it does. Acetyl-Coenzyme A is turned into fat. But you see, the overall signals in the body are "we've got a lot of energy around! Save energy!" That means entering storage mode, cells capture free sugar and accumulate it internally, any sugar past the cell reserves is turned into fat, etc, etc.
But then you're hungry, because that's a response triggered by blood sugar. The liver's accumulating everything it can because it's flooded by Acetyl-Coenzyme A, but the rest of the body has suddenly less blood sugar than it'd like.
Metabolic interactions can be a funny thing.
