You'll feel pretty lethargic at first, but like BTB said it'll pass in a couple days. Quicker if you really pound down the fats and restrict the carbs, forcing your body to go through a metabolic shift. But the twice weekly carb re-feeds might make that difficult. You could always just have one really big carb re-feed on like Wednesday (if you train on Wednesdays) post workout. Then the other one could be all day Sunday. That's something that works for me really well.
Dark chocolate, macadamia nut oil (olive oil works well too), avocados, peanut butter, regular butter if you're feeling feisty. Might as well eat a block of cheese too if you like cheese.
"There is no passion, without some obsession."