When it comes to nutrition and diet, calories can be a good rule of thumb to make sure your portion sizes stay in check, but they aren’t the full story. They're also hard to measure accurately. A large boiled egg is expected to be 50 calories, but it depends on whether the chicken was free-range, organic, corn-fed, battery, and so on. In theory you could get your 2,000 calories a day in chocolate, but your body wouldn't thank you for it. It's the quality of the food you eat that matters.