I knew that the whole MyFitnessPal calories in vs. calories out thing was too simple to be right. Just when I credited my 53-pound weight loss to paying attention to my net calorie intake, I find out that I’ve gotten it all wrong. It seems that there’s a “degree of difficulty.”
Scientists have long measured calorie content by burning a carefully measured portion of the food in a special device, a calorimeter. As it turns out, your body doesn’t use fire to break down food, and the system it does use produces different reality from what the calorimeter would suggest. According to an article in The New York Times:
The system is most accurate when the foods are easily digested and all of their energy is made available to the body as they are when consuming highly processed carbohydrates. But in the past few decades, scientists have begun to understand that a substantial number of calories are lost in the effort to digest food. For example, meat and nuts are harder to break down, and so the body expends energy trying to digest them.
This is yet another great reason to eat more whole foods and fewer processed gunk. Since the processed stuff–say white bread vs. whole grain bread–requires more effort for your body to digest, two servings of bread with the same supposed calorie content will have a different impact on your body.