Its not so much because of the calories, just its unadvisable - I read about it before, and the science-y bit was a bit too much for me, but basically you get drunk a heck of a lot faster. Also, when you are in ketosis your bodys breaking down fat and producing ketones which fuel your body. Alcohol can stop this so you don't have the fuel to work your body or your brain. Its probably more likely on diets like this because its low cal as well as low carb.
The chances are, if you drink your likely to just get a slightly worse hangover than normal.... but theres the small potential that if your body reacts badly it could harm or even kill you
