One pound of fat is 3500 calories. A calorie is a unit of energy just as a dollar is. But some are worse than others. I used to love me a regular Quarter Pounder with cheese–a 500 calorie gut bomb. The last time I ate one I knew I was going to feel like shit right after. I ate the burger and promptly felt like shit. I also used to love eating the large orders of french fries, sausage egg and cheese McGriddles, baked apple pies (always two) and blueberry muffins, each about 500 calories.