I think calories do matter...just not to the extent that many people think they do. If you eat 3500 extra calories you won't gain exactly one pound. You might gain nothing; you might gain 5 lbs. in water weight; anything could happen. Calories matter in a *general* sense (you can't eat 6000 calories a day with no carbs and expect your body not to be forced to store any of that) but I don't think your body will respond exactly the same way each time to the same amount of calories.