Karin has given a scientifically correct answer.
Adding to her answer, a Calorie is 1000 calories, or one Kilocalorie (kcal). The difference here is the capital C. The calories that are in food are measured in kcals, that’s why they’re Calories, not calories. Also, one liter of water weighs about one kilogram. Consider the amount of water (percent composition) in the human body. Cells in the human body are actually anywhere from 70-95 percent water (varies by function and type). Also consider the the average temperature of the human body that is maintained through homeostasis (98.6 degrees fahrenheit). Convert that to Celsius. It can get complicated, but you can begin to get a sense of how much energy it actually takes to keep the body at this temperature. A large portion of your caloric intake is devoted to maintaining core temperature.
For 1 gram of protein, there are 4 kcals
For 1 gram of carbohydrates there are 4 kcals
For 1 gram of alcohol there are 7 kcals (this is why beer with less calories generally has a lower alcohol content and doesn’t have as much of an “effect” as regular beer, just as an example)
For 1 gram of fat, there are 9 kcals
Check your food labels and you should see that if you take the *per serving* grams of protein, carbohydrates, and total fat, multiply those numbers by the appropriate kcal amount, you should find that the result will be equivalent to the calories per serving! Cool huh?
Also keep in mind that if something contains .49g of trans fat or less, the food label CAN say 0g of trans fat. This is just something to keep in mind that can sometimes skew the Calorie count based on the macronutrient content (macronutrients being protein, carbohydrates, and fat). Food labels are more “approximations” than EXACT measurements. They are suffciently accurate, however! Generally the .49g of trans fat won’t have much of an overall effect on your diet unles you eat a lot of these foods. All things in moderation, and moderation of all things.