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1.4: Calories (Food Energy)

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    Food energy is measured in kilocalories (kcals), commonly referred to as calories. This terminology is technically incorrect, but is used so commonly that we will refer to them as calories throughout the course. A kilocalorie is the amount of energy needed to raise 1 kilogram of water 1 degree Celsius. A food’s kilocalories are determined by putting the food into a bomb calorimeter and determining the energy output (energy = heat produced). The first link below is to an image of a bomb calorimeter and a link to a video showing how one is used.

    Web Links

    Bomb Calorimeter

    Video: Bomb Calorimetry (2:19)

    Among the nutrients, the amount of kilocalories per gram that each provide are shown below.

    Energy (kcal/g) No Energy
    Carbohydrates (4) Vitamins
    Proteins (4) Minerals
    Lipids (9) Water

    As can be seen, only carbohydrates, proteins, and lipids provide energy. However, there is another energy source in the diet that is not a nutrient… alcohol. Just to re-emphasize, alcohol is NOT a nutrient! But it does provide energy.

    Figure 1.112.png

    Figure 1.112 Wine is a type of alcohol.

    The following table lists the energy sources in the diet from lowest calories per gram to the highest calories per gram. Knowing these numbers allows a person to calculate/estimate the amount of calories the food contains if you know the grams of the different energy sources.

    Energy Sources (kcal/g)

    Carbohydrates → 4

    Protein → 4

    Alcohol → 7

    Lipids → 9

    Contributors and Attributions


    This page titled 1.4: Calories (Food Energy) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Brian Lindshield via source content that was edited to the style and standards of the LibreTexts platform.