An apple a day surely keeps the doctor away. That's the cliche we commonly know. But apples also keep the dentist and the calories away! How? Apple is one of the fruits listed under the still-doubted-findings of negative calorie foods.
All foods contain calories together with nutrients, vitamins and minerals. So no, there is no such thing as negative calories, it only means that one who eats these certain foods need more energy than what the food has in order to metabolize/break it down.
Say an apple contains 100 calories but your body needs about 150 calories to burn it, 50 calories are borrowed from your stored calorie content...thus the more you eat apples, the more calories you burn.
Aside from apples, diverse vegetables are listed as well. Here are some of them, be sure to grab any once in a while:
asparagus, cranberries, beet, grapefruit, broccoli, lemon mango, carrot, orange, cauliflower, pineapple, celery, raspberries, green cabbage, strawberries, hot chili peppers, lamb's lettuce, cucumber, lettuce, endive, onion, garden cress, papaya, garlic, spinach, green beans, turnip, zucchini.
Here's to healthy eating! =)