Ever glanced at the back of a food packet and seen that bold number staring back at you? Calories. For over a century, this single unit has dominated our conversations about food, health, and weight. We count them, burn them, and often, feel guilty about them. But have you ever wondered where this powerful little number came from? The story is a fascinating journey involving French chemists, German physiologists, American innovators, and surprising facts you won’t find on any food label.
Our story begins not in a kitchen, but in a Parisian laboratory in the 1780s. The brilliant French chemist Antoine Lavoisier proposed a radical idea: breathing is a form of combustion, just like a candle burning. To prove it, he and his colleague Pierre-Simon Laplace built a device called an ice calorimeter, large enough to house a guinea pig. By measuring the heat the animal produced (by how much ice it melted), they linked the energy of life to the physics of heat. Soon after, the word “calorie,” from Latin for heat, was coined to measure this energy.
For decades, the calorie remained a tool for physicists and engineers. Its journey into our diets began with a German baron, Justus von Liebig, who was concerned about malnourishment. In the 1840s, he developed a concentrated beef extract to provide cheap, energy-rich food for the poor: a product we know today as the Oxo cube. His students, inspired by his work, began meticulously measuring the energy the human body extracted from different foods. One of them, Max Rubner, established that proteins, fats, and carbohydrates could be measured by their equivalent heat value. This simple idea — that different foods could be compared through a single number — laid the groundwork for every diet fad to come.
The calorie truly went global when an American chemist, Wilbur Olin Atwater, studied in Germany and brought the science back to the US. In the 1890s, he published influential government bulletins that calculated the energy values of hundreds of foods. It was Atwater who established the capitalised “Calorie” (actually a kilocalorie, or 1,000 small calories) that we now see on US food labels.
But science alone didn’t make the calorie a household name. Fashion did. In the roaring twenties, physician Lulu Hunt Peters published her blockbuster book, Diet and Health. She brilliantly linked calorie counting to the trendy “flapper” ideal: a thin, boyish figure that symbolised a modern, liberated lifestyle. Suddenly, counting calories wasn’t just for scientists; it was a chic tool for self-transformation. The ordinary act of eating was forever changed, governed by arithmetic.
However, the original motivation for counting calories wasn’t personal health or beauty. It was about social control and efficiency. Early nutritionists studied prisoners, factory workers, and the impoverished to determine the minimum amount of fuel needed to keep them productive without causing food riots. The goal was to find the cheapest way to feed the masses in institutions such as schools, the military, and workhouses.
A question of justice — how to feed the hungry — was reframed as a problem of cost and management.
Today, science is revealing the limits of this 18th-century idea. The simple model of “calories in, calories out” is being challenged. We now know that the numbers on food labels are averages, with significant margins of error. More importantly, our bodies are not simple furnaces. How we absorb energy depends on our unique genes, gut bacteria, and even the way food is cooked. Not all calories are created equal; 200 calories of almonds are processed very differently from 200 calories of fizzy drink.
The future of nutrition lies in a more personalised and complex understanding. Fields such as nutrigenomics are exploring how our individual genetic makeup interacts with the food we eat. We are slowly moving away from the simple act of counting and towards understanding the intricate relationships within our bodies.
Calories gave us a language to talk about food energy, but it’s a language that’s now due for an update. So, the next time you look at that number on a label, remember its rich and complicated history — a story of guinea pigs, beef cubes, and flappers — and know that we are far more complex than a simple calculation.
Jahnavi Phalkey is the founding director, Science Gallery Bengaluru.
Published – October 14, 2025 06:00 am IST