Do you keep track of what you eat during these tournaments?

I would assume you would have at least a somewhat different diet during these days and your mind would be more focused on the tournament then what you are going to eat, and you might forget to eat enough. It's like going into survival mode when you are focusing on something important to you. Most likely it is a combination of eating less calories and burning more, if you are losing a noticeable amount of weight in a couple days.