13/03/2013 13:47 GMT | Updated 13/05/2013 06:12 BST

Why Calories Don't Count - Part 1 of 5


Calories are the main stay of conventional dietary advice but when we take a proper look at calories, they're not actually that scientific... (Feel free to watch the video of this article below!)

Calories were created in 1824 by Nicolas Clément and were originally used to measure heat, originating in studies concerning fuel efficiency for the steam engine. They've since been the staple in terms of measuring energy in foods, but what actually is a calorie? A calorie is the amount of energy it takes to raise the temperature of one kilogram of water by one degree on a Celsius thermometer at sea level. Don't worry that doesn't mean much to me either.

The way nutrition scientists measure calories in food is by burning the food in a bomb calorimeter. Which is a box with two chambers, one inside the other. The scientists 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 inner chamber 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 one degree per kilogram, the food has one calorie; two degrees, two calories; and 235 degrees, 235 calories. Sounds scientific enough doesn't it?

But my question is this, what on earth does that have to do with all the bodily processes that are involved in digesting food?

The answer... not much!

Now don't get me wrong, in terms of weight management having the right energy balance is important, you can have too much energy or too little energy from food. Calories can give you sort of a ball park figure, but for measuring energy in food, especially for weight loss, they aren't particularly accurate or even scientific.

On a basic analysis of calories they don't take into account how the body processes the three different macro-nutrients of food; carbohydrates, protein and fat, each one is processed very differently in the body. For instance if I was to eat 2,500 calories of bread, mainly carbohydrates, versus eating 2,500 calories of salmon with broccoli, mainly fat, my body would have very different reactions.

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