A calorie is a unit that is used to measure energy. The Calorie you see on a food package is actually a kilocalorie, or 1,000 calories. A Calorie (kcal) is the amount of energy needed to raise the temperature of 1 kilogram of water 1 degree Celsius.
Nutrition scientists measure the number of calories in food by actually burning the food in a bomb calorimeter, which is a box with two chambers, one inside the other. The researchers weigh a sample of the food, put the sample on a dish, and put the dish into the inner chamber of the calorimeter.
They fill the inner chamber with oxygen and then seal it so the oxygen can’t escape. The outer chamber is filled with a measured amount of cold water, and the oxygen in the first chamber (inside the chamber with the water) is ignited with an electric spark. When the food burns, an observer records the rise in the temperature of the water in the outer chamber. If the temperature of the water goes up 1 degree per kilogram, the food has 1 calorie; 2 degrees, 2 calories; and 235 degrees, 235 calories — or one 8-ounce chocolate malt!
So I don’t know about you but I am pretty sure that our bodies are a bit different then a bomb calorimeter!! State of metabolic health, mix of macros, age activity, etc all have affects on how and where the energy from food goes and how much energy we get from it. Now add on top of that no real accurate way (outside a lab setting) to measure calories burned, and you start to get a picture of why the counting of calories and CICO is so flawed!
Poor Misunderstood Calorie is a great book that delves deeply into why a calorie is not a calorie and is a great read, I highly recommend it! Also the accompanying blog http://www.caloriesproper.com is a great further education source!
Some suggested further reading/viewing:
Nutrition Forum – Dr. Donald Layman, PhD
Dr. Layne Norton presents on Refractory Phenomenon
The need for Protein throughout the day
ENERGY BALANCE MATTERS
but the counting of calories is severely flawed!! — with Helga Middleditch.