When Did People First Start Counting Calories?

December 5, 2025 •

4 min read

The word "calorie" was first defined in the 1820s by French chemist Nicolas Clément, though the practice of using calories for nutrition and weight management did not become popular until much later. The story of when did people first start counting calories reveals a complex journey from engineering laboratories to public health campaigns and weight-loss trends.

Quick Summary

The concept of the calorie evolved from 19th-century physics to popular weight-loss culture in the 20th century, popularized by key figures like Wilbur Atwater and Lulu Hunt Peters. The initial focus was on worker productivity and food economy before shifting dramatically towards individual dieting.

Key Points

Origin in Engineering: The concept of the calorie originated in 19th-century physics to measure the energy output of machinery, not for human nutrition.
Atwater's Nutritional Application: American chemist Wilbur O. Atwater first applied the calorie to human nutrition in the late 1800s, using calorimeters to measure food and metabolism.
Popularized for Dieting: Dr. Lulu Hunt Peters popularized calorie counting for weight loss with her 1918 bestselling book, Diet and Health: With Key to the Calories.
Shift to Diet Culture: The practice of calorie counting shifted from a scientific and economic tool to a cultural phenomenon focused on individual dieting in the early 20th century.
Evolution of Methods: The initial direct calorimetry method was later refined into the Modified Atwater system, which more accurately reflects metabolizable food energy.
Modern Understanding: Contemporary science recognizes that focusing solely on calorie counts is an oversimplification, with factors like food quality and hormonal balance also playing crucial roles.

From Steam Engines to Science: The Calorie's Origins

The story of the calorie begins not in a nutrition lab, but with the study of heat and energy in 19th-century engineering. In the 1820s, French chemist Nicolas Clément defined a "calorie" as the heat required to raise the temperature of a kilogram of water by one degree Celsius. This initial definition, however, was not immediately linked to human food consumption. For decades, the term remained primarily within scientific and industrial circles, used to measure the energy output of machinery like steam engines.

The American Pioneer: Wilbur O. Atwater

The late 19th century marked a pivotal shift, thanks to the work of American chemist Wilbur O. Atwater. After studying human metabolism in Germany, Atwater returned to the United States and began conducting experiments to measure the energy value of food and the metabolic rate of humans. Using a "bomb calorimeter," he burned food samples to calculate their heat content. He also developed a sophisticated human respiration calorimeter to measure a subject's metabolic heat output while performing various activities. Atwater's research established the caloric values of protein, carbohydrates, and fat that are still used today, forming the scientific foundation for modern calorie counting. His work was initially driven by a desire to improve the diets of workers and address malnutrition, emphasizing food economy rather than weight loss. In 1887, he published articles in Century magazine that first introduced the concept of food energy to a wider American audience, using the capitalized "Calorie" to refer to the larger unit (kilocalorie).

Popularization and the Rise of Diet Culture

While Atwater provided the scientific framework, it was a bestselling author who truly brought calorie counting to the masses as a weight-loss tool. In 1918, Dr. Lulu Hunt Peters published Diet and Health: With Key to the Calories, a book that became immensely popular. Peters' book demystified the calorie and provided easy-to-understand charts, making calorie counting a practical method for individual weight control. This coincided with a societal shift towards a thinner body ideal in the 1920s, especially among women. For the first time, fatness was increasingly viewed not as a sign of prosperity but as a personal failing, and calorie counting was presented as the scientific solution to this perceived problem. Peters' work, along with food conservation efforts during World War I, cemented the calorie's place in public consciousness, transitioning it from a technical scientific measure to a cultural phenomenon.

The Evolution of Calorie Calculation and Understanding

Since Atwater's foundational work, the methods for determining and understanding calories have evolved. The initial direct calorimetry method, while accurate for the heat content of food, was limited because it didn't account for how the human body actually digests and absorbs nutrients.

Atwater vs. Modified Atwater


Feature	Original Atwater System (Late 19th Century)	Modified Atwater System (Present Day)
Calculation Method	Direct calorimetry; burned food in a bomb calorimeter to measure heat output.	Indirect method; uses chemical analysis and standard conversion factors for macronutrients.
Accounting for Absorption	Included energy from indigestible fiber and other compounds, overestimating usable energy.	Excludes indigestible fiber content and adjusts for partial absorption by the body.
Factors Used	Calculated values of ~4.1 kcal/g for protein and carbs, and ~9.3 kcal/g for fat.	Utilizes standard factors: 4 kcal/g for protein and carbs, 9 kcal/g for fat, and 7 kcal/g for alcohol.
Accuracy	Prone to overestimation of the energy the human body can actually utilize from food.	More accurately reflects the metabolizable energy available to the body from food sources.

Beyond the Basic Count

Modern nutritional science recognizes that not all calories are created equal and that simply counting them doesn't provide the whole picture. Factors such as the thermic effect of food (the energy required to digest and absorb nutrients), hormone balance, and the gut microbiome all influence how the body processes and utilizes energy. Research in the 21st century has shifted focus from single nutrients to the importance of overall dietary patterns and food quality for preventing chronic diseases like diabetes and cardiovascular disease. Nevertheless, the calorie remains a foundational metric for understanding food energy and its relationship to the body.

Conclusion: A Complex Legacy

The journey of the calorie, from a unit of heat for steam engines to a central metric of modern diet culture, reflects broader shifts in science, economics, and societal ideals. While pioneers like Wilbur Atwater and Lulu Hunt Peters helped popularize the concept for nutritional and weight-management purposes, our understanding has evolved considerably. Today, while counting calories is still a common practice, it's widely understood as only one part of a complex and personalized nutritional picture. It serves as a reminder that science, society, and our relationship with food are constantly in flux.

Calorie Counting, Difference, and Citizenship in 19th- and 20th-Century America - Oxford Research Encyclopedias

Frequently Asked Questions

The term "calorie" was first defined in the 1820s by French chemist Nicolas Clément during his lectures on heat engines, defining it as the heat required to raise the temperature of a kilogram of water.

Wilbur O. Atwater was an American chemist who pioneered the application of the calorie to human nutrition in the late 19th century. He developed calorimeters to measure the energy in food and human metabolism, creating the foundation for the calorie counts used today.

Calorie counting was popularized as a weight-loss method by Dr. Lulu Hunt Peters, whose 1918 book, Diet and Health: With Key to the Calories, made the concept accessible to the general public. This coincided with a cultural shift that began to link thinner physiques with health and moral character.

A nutritional "Calorie" (with a capital C) is technically a kilocalorie (kcal), which is 1,000 small calories. The small calorie (cal) is the energy needed to heat one gram of water by one degree Celsius, while the larger Calorie heats one kilogram.

Modern food labels use a version of the Atwater system, which is a standardized and more accurate method than early measurements. It accounts for the different energy yields of protein, carbohydrates, and fats in the human body, though it is not perfectly precise for every individual.

Yes, historians argue that the popularization of calorie counting, combined with a cultural shift towards thinner ideals, contributed to the emergence of fat stigma in the early 20th century. Fatness began to be framed as a controllable individual failing.

Nutritional science has evolved to recognize that food is more complex than just its calorie count. Modern research focuses on overall dietary patterns, food quality, and individual metabolic factors, moving beyond the simple 'calories in, calories out' model.