The French Origins of the Calorie
Antoine Lavoisier's experiments in the late 1700s on calorimetry provided a basis for understanding heat, but it was French chemist and engineer Nicolas Clément who formally defined the calorie unit around 1824 {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. Clément defined a large calorie in his lectures as the amount of heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius, primarily for understanding steam engines {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. This definition was later recorded by his students and became influential, appearing in a French dictionary in 1845.
The Rise of Calorie Confusion
Throughout the 19th century, the calorie concept saw varying definitions. French chemists in the 1850s used a smaller calorie based on heating 1 gram of water, contrasting with Clément's kilogram-based unit used by physicists and engineers. In 1879, French chemist Marcellin Berthelot proposed using 'calorie' (cal) for the gram-based unit and 'Calorie' (Cal) or kilocalorie (kcal) for the kilogram-based unit, a convention that didn't fully resolve the confusion {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}.
The American Push for Nutritional Calories
American chemist Wilbur Olin Atwater played a significant role in bringing the calorie into the realm of popular nutrition in the late 19th century {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. Atwater applied calorimetric methods learned in Europe to American contexts {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. He introduced the food Calorie (kilocalorie) to the American public through articles in Century Magazine starting in 1887 {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. Atwater and his team established the caloric values for macronutrients still widely used today {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. Atwater's work influenced public health and diet books, including a 1918 guide which popularized calorie counting for weight loss {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}.
Comparison of Calorie Types
Historically, two main calorie definitions emerged:
| Feature | Small Calorie (cal) | Large Calorie (Cal or kcal) |
|---|---|---|
| Definition | Heat needed to raise 1 gram of water by 1°C {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. | Heat needed to raise 1 kilogram of water by 1°C {Link: ScienceDirect.com https://www.sciencedirect.com/science/article/pii/S0022316622085546}. |
| Equivalence | 4.184 Joules | 4.184 Kilojoules (1,000 small calories). |
| Context | Primarily used in physics and chemistry research. | Standard unit for food energy on nutritional labels {Link: oxfordre.com https://oxfordre.com/foodstudies/display/10.1093/acrefore/9780197762530.001.0001/acrefore-9780197762530-e-122}. |
| Common Use | Scientific calculations. | Public health and dietetics {Link: oxfordre.com https://oxfordre.com/foodstudies/display/10.1093/acrefore/9780197762530.001.0001/acrefore-9780197762530-e-122}. |
The Modern Context: Joules and Lingering Confusion
Public confusion between the small and large calorie persists. The joule (J), the standard SI unit of energy adopted in 1948, has largely replaced the calorie in science due to its more consistent definition {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}. Despite this, the calorie remains prevalent in nutritional discussions and food labeling {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
Conclusion
The concept of calories, while building on Antoine Lavoisier's calorimetry work, was formally defined by Nicolas Clément in the 1820s. Different definitions caused confusion throughout the 19th century until Wilbur Olin Atwater popularized the calorie for nutritional science in the United States, forming the basis for modern food energy labeling {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}. Though scientists now prefer joules, the calorie remains a key concept in diet and health {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
The Pioneers Behind the Calorie
- Antoine Lavoisier: Performed foundational 18th-century calorimetry experiments {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
- Nicolas Clément: First defined the term "calorie" around 1824 for heat engines {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
- Marcellin Berthelot: Proposed the 'cal' and 'Cal' convention in 1879 {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
- Wilbur Olin Atwater: Popularized the food calorie in the U.S. and developed methods for calculating food energy {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
- Lulu Hunt Peters: Authored a best-selling 1918 book that popularized calorie counting for weight loss {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
For more detailed information on the history of calorimetry and the development of energy units, see the article on the topic at the Science History Institute.
How Was the Calorie Used in Early Science?
Initially, the calorie was a technical unit for measuring heat in engines and experiments {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
How Did the Calorie Enter Public Consciousness?
Wilbur Olin Atwater's articles connected food energy to bodily fuel needs, and later, authors like Lulu Hunt Peters simplified this for weight loss purposes {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
Is There a Difference Between "Calorie" and "kilocalorie"?
Yes, a kilocalorie (kcal) or large Calorie (Cal) is 1,000 small calories (cal) {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}. Food labels use "calories" to mean kilocalories {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
Why is the calorie an outdated scientific unit?
It's largely replaced by the joule (J) in science, which is the standard SI unit of energy {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
How is food energy actually measured?
Food energy is measured through calorimetry, where a food sample is burned and the heat released calculates its energy content {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
How did Lavoisier contribute to the concept of calories?
Lavoisier's experiments were foundational to calorimetry, though he didn't create the calorie unit {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
When did calorie counting for weight loss begin?
Calorie counting for weight loss became popular in the early 20th century, influenced by diet books that simplified scientific concepts {Link: nutritionj.biomedcentral.com https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-6-44}.
