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How are Dietary Calories Calculated?

Jessica Ellis
Updated Mar 03, 2024
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A calorie is a scientific measurement, used in determining the energy produced by a unit. A dietary calorie is used to measure the output of energy in food, and can be helpful in setting daily limits of food that can be successfully burned by the body. A dietary calorie is equal to 1000 small calories, and will raise the temperature of one kilogram of water one degree C (1.8 ° F.)

The calorie measurement was first determined by a French physicist named Nicolas Clement in 1824. Despite its popular use in the American dietary standards as set by the United States Department of Agriculture (USDA), food energy is more often determined worldwide by units called joules. A calorie is equal to 4.1868 kilojoules.

Dietary calories contained in food are often initially determined by measuring the energy output in a calorimeter. In reaction and bomb calorimeters, an insulated container is used to cause a chemical process that makes the contained energy react over time. The amount of calories is measured by calculating the heat output and the time used. There are several varieties of calorimeter available, including X-ray and heat-loss versions. Although the methods of measurement are different, the resulting calculation of a specific sample will be nearly identical regardless of which variety of calorimeter is used.

The Atwater system is another method of calculating the dietary calories in a food. Nutrients tend to have a specific caloric value per gram, which is often used to obtain caloric information. For instance, carbohydrates and protein both have about four calories per gram, while fat has nine calories per gram. If you see a packaged food that shows these conversions, the dietary calories in the food have likely been calculated using the Atwater system rather than traditional calorimeters.

Unfortunately, the Atwater system is far from perfect. Some carbohydrates contain insoluble fiber that cannot be digested by the body, leading to necessary adjustments in the caloric calculation. Critics argue that the Atwater system of measuring dietary calories is too general, and will not give you the correct calories for every individual sample.

The understanding of dietary calories is important in determining what comprises a sustainable diet. Unlike animals, which generally eat whatever is nearby and are often drawn to necessary nutrition, humans can consume a wide variety of substances that are completely unnecessary to provide nutrition and energy. With obesity rates skyrocketing in the 21st century, it is clear that many people do not understand what constitutes enough food or correct food to sustain the body and provide it with a correct level of energy. Determining the amount of dietary calories in foods is the first step to determining the correct amount of food that should be consumed, based on current weight, activity level, and health status. Now more than ever, correct calculation of dietary calories by the Atwater system and calorimeters is necessary to ensure the health of human beings.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Jessica Ellis
By Jessica Ellis , Writer
With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis brings a unique perspective to her work as a writer for The Health Board. While passionate about drama and film, Jessica enjoys learning and writing about a wide range of topics, creating content that is both informative and engaging for readers.

Discussion Comments

By anon151824 — On Feb 11, 2011

looking for a way to easily determine calories in

food cooked at home. Tried to find info on a

calorimeter without success.

Jessica Ellis

Jessica Ellis


With a B.A. in theater from UCLA and a graduate degree in screenwriting from the American Film Institute, Jessica Ellis...
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