We need to scarf down plenty of calories in a day, but if you’ve got a nasty snack habit that’s tipping the scales to heavy, weblog Bootstrapper’s list of 15 foods that burn more calories than they contain might be the perfect addition to your grocery list. Called negative calorie foods, the following 15 treats actual burn more calories in their digestion than they offer, so you can fulfill your snack craving without the guilt of a bag of potato chips. From apples to zucchini, these…