– if carbohydrates are the body’s energy source, what exactly are calories?

Question

I keep hearing that carbs are the body’s fuel, but fats contain more calories per gram. Surely that means fat is the body’s primary source of fuel?

In: 3

Answer 1

a “calorie” is a measurement of energy and in food what we call calories are really “kilo-calories” or calories x 1000.

It doesn’t matter what energy you are measuring, you can measure the energy generating from burning wood or gasoline or a nuclear bomb in calories, we just don’t.

So in the case of food humans are capable of deriving energy directly from carbohydrates and getting X calories out per unit of carbs. The same with proteins and fats, we can extract energy from a ton of different food sources if we need to.

Our metabolism prefers to burn carbohydrates directly from our blood stream as it’s primary energy source, and typically a surplus blood-stream carbs are converted to fats for long term storage.

If your diet or situation requires it, we can draw from stored fats directly for energy but it’s not preferred. For example, if you’ve heard of endurance athletes “hitting the wall” that’s typically when they run out of carbs and start burning stored fats directly.

Similarly for low carb diets like Keto, you are training your body to prefer the burning of fats due to a lack of carbs.

In extreme cases the body can start burning its proteins (essentially your muscles) directly into energy but this is not preferred and is basically a stage of starvation.