Health & Fitness Tips - Eat negative calorie foods:
Although no food is actually "negative calorie", there are certain foods that have such few calories that the act of digestion in the body will burn more calories than the food itself, creating a negative calorie balance. Typically, a 25 calorie piece of broccoli (100 grams) requires 80 calories to digest it in the body which results in a net loss of 55 calories! Some great foods which are extremely low in calories and require lots of energy for the body to break them down include asparagus, broccoli, cauliflower, celery, lettuce and zucchini. These are great foods to include in your weight loss plan.

More at: http://www.fitnessattitudes.com/negative.html