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Energy Sources

Author(s): Nancy Moreno, PhD, and Paula Cutler, BS.

Measuring Energy

One calorie is defined as the amount of energy needed to raise the temperature of one gram of pure water (equivalent to one milliliter of water) by one degree Celsius. Students can approximate the calories in each of the foods tested by multiplying the temperature change in each case by 50. This measure, of course, is just an estimate. Calorie content actually is measured in a calorimeter in which all conditions are carefully controlled.

Carbohydrates, fats and proteins are the main energy sources in foods. Sugars, starches (such as those in breads, pasta and potatoes) and fiber (as in bran and many vegetables) are the primary forms of carbohydrates. Foods rich in fats include animal and vegetable oils, lard, butter and cream. Proteins, the building blocks of muscles and molecules within cells, are present in meats, as well as in plant materials, such as nuts and beans. In this activity, the oat cereal consists almost entirely of carbohydrates (sugar and oat flour). The pecan contains both proteins and oil. The oil content contributes to the higher calorie content of the nut on a per-gram basis. At the same time, nuts are a denser food than the baked cereal, which also contributes to their higher calorie content.

The calories reported on most food labels represent one kilocalorie, or 1,000 calories, and often are written with an uppercase “C.”

Carbohydrates and proteins supply four Calories (kilocalories) per gram. Fats and oils provide about nine Calories per gram. 


Funded by the following grant(s)

National Space Biomedical Research Institute

National Space Biomedical Research Institute

This work was supported by National Space Biomedical Research Institute through NASA cooperative agreement NCC 9-58.