How were calories in food discovered?

December 12, 2025 •

3 min read

The idea of quantifying food energy emerged in the 18th century, but its standardized use in nutrition took decades of scientific refinement. Discover how scientists, starting with pioneering chemists, figured out how were calories in food discovered and applied to everyday life.

Quick Summary

The measurement of food energy evolved from early combustion experiments by Lavoisier to the development of the bomb calorimeter and the Atwater factors used on modern nutrition labels.

Key Points

Lavoisier's Contribution: In the 18th century, chemist Antoine Lavoisier demonstrated that respiration was a combustion process, establishing the first link between heat and metabolic activity using an ice calorimeter.
The Term 'Calorie': French physicist Nicolas Clément introduced the term 'calorie' in the 1820s, defining it as the heat needed to raise one kilogram of water by one degree Celsius.
The Bomb Calorimeter: In the late 19th century, Marcellin Berthelot and other scientists developed the bomb calorimeter, allowing for the precise measurement of heat released by burning food.
Atwater's Pioneering Work: American chemist Wilbur Olin Atwater used bomb calorimeters and human respiration chambers to quantify the energy values of proteins, fats, and carbohydrates in the 1890s.
The Atwater System: The modern Atwater System, which assigns standardized caloric values (e.g., 4, 9, 4) to macronutrients, is based on Atwater's extensive research and is used for food labeling today.
Legacy of a Discovery: The calorie discovery was a cumulative effort spanning decades, with early calorimetry principles evolving into the practical, indirect calculation system used globally in nutrition science today.

The Founding Principles: Early Calorimetry

The story of discovering calories begins with fundamental questions about combustion and heat. In the late 18th century, French chemist Antoine Lavoisier and physicist Pierre-Simon Laplace conducted experiments demonstrating that animal respiration was a form of slow combustion.

The Ice Calorimeter

Using an ice calorimeter, Lavoisier and Laplace measured the heat produced by a guinea pig, linking metabolic activity to heat output. This was a crucial early step in understanding food energy.

The Naming of the Calorie

The term "calorie" was introduced later by French physicist Nicolas Clément in the 1820s as a unit of heat for steam engines, defined as the heat needed to raise one kilogram of water by one degree Celsius.

Resolving the Confusion

Confusion arose as other scientists used a smaller unit based on heating one gram of water. In 1879, chemist Marcellin Berthelot proposed distinguishing the larger unit as 'Calorie' (kilogram-calorie) and the smaller as 'calorie' (gram-calorie). This capitalization convention was later adopted by Wilbur Olin Atwater.

The Bomb Calorimeter and Atwater's Era

The bomb calorimeter, developed by Berthelot in 1881, allowed for the precise measurement of heat released when a substance was burned in a sealed, oxygen-filled container submerged in water.

The American Father of Nutrition Science

Wilbur Olin Atwater, considered the father of modern American nutrition science, used bomb calorimetry to determine the caloric values of proteins, carbohydrates, and fats. He and Edward Bennett Rosa also developed a respiration calorimeter to study human energy balance, confirming that energy consumed equals energy expended plus stored energy.

A Timeline of Key Developments in Calorie Discovery

Late 1700s: Lavoisier and Laplace demonstrate respiration as combustion using an ice calorimeter.
1820s: Nicolas Clément introduces the term 'calorie'.
1852: Favre and Silbermann use a different calorie unit.
1879: Marcellin Berthelot clarifies the 'small' and 'large' calorie distinction.
1881: Berthelot develops the bomb calorimeter.
1890s: Wilbur Olin Atwater conducts extensive calorimetry experiments.
Early 1900s: Atwater publishes food composition tables and the Atwater System.

Modern Calorie Calculation: The Atwater System

Food labels today use the Atwater System, an indirect method based on Atwater's research. This system assigns standard caloric values to macronutrients, providing a practical approach for the food industry.


Feature	Bomb Calorimetry (Direct)	Atwater System (Indirect)
Method	Burns a food sample to measure the heat released directly.	Calculates energy by summing the standard values of macronutrients.
Accuracy	Very precise for measuring total potential energy in a food sample.	Practical and standardized, but can be less precise for individual foods due to variable digestibility.
Process	Destructive; requires specialized lab equipment and a controlled environment.	Non-destructive; relies on chemical analysis of macronutrient content.
Real-World Application	Historically used to set baseline energy values for macronutrients.	The standard method for generating nutrition labels found on food packaging today.
Energy Values	Measures total heat of combustion.	Uses average values for digestible energy (e.g., 4 kcal/g carbs, 9 kcal/g fat).

Conclusion: From Combustion to Calculation

The discovery and measurement of food calories is a scientific journey from Lavoisier’s early work on respiration to Atwater’s comprehensive quantification of macronutrient energy. The calorie counts on modern nutrition labels, based on the Atwater system, are a direct result of this historical scientific inquiry, offering consumers a practical, though generalized, measure of food energy.

Frequently Asked Questions

The concept of measuring metabolic heat began with Antoine Lavoisier in the 1780s, but the term 'calorie' was first coined by Nicolas Clément in the 1820s. American chemist Wilbur Olin Atwater solidified its use in nutrition in the late 19th century.

The first experiments, conducted by Lavoisier, aimed to prove that animal respiration was a process similar to combustion by measuring the heat produced. The goal was to understand metabolic processes, not just food energy.

A bomb calorimeter is a scientific instrument used to measure the energy content of food by burning a sample in a sealed container and measuring the heat released. The resulting temperature change in the surrounding water is used to calculate the caloric value.

A 'Calorie' (capital C) or kilocalorie (kcal) is the unit of food energy most people are familiar with. A 'calorie' (lowercase c) is a much smaller unit of energy, defined as the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. One Calorie is equal to 1,000 calories.

The Atwater System is the method used today to calculate the approximate caloric content of foods. It assigns average energy values to each gram of protein (4 kcal), carbohydrate (4 kcal), and fat (9 kcal), rather than burning every product.

Calorie counts on food labels are based on the Atwater System, which uses average energy values. They are generally accurate enough for nutrition tracking, but they are estimates. Factors like how your body digests food can cause some variation.

The joule is the international standard unit of energy for scientific use. Since calories represent heat energy, they can be converted to joules (1 Calorie = 4.184 kilojoules). Both are valid energy units, though the Calorie is more common in nutrition.