An observer and operator outside a human calorimeter, ca. 1910 (Courtesy of the U.S. Department of Agriculture National Agricultural Library) 

Inside this large experimental box, men did paperwork and women washed laundry as part of experiments to determine the amount of energy in food. Wilbur Atwater built these chambers large enough so that human subjects could live in them for several days. Atwater and his co-workers controlled the amount of food going into the calorimeter, the activities of the subjects, and the amount of waste coming out. By measuring the amount of heat the subjects produced, Atwater’s team was able to determine the amount of energy in the foods they ate. Atwater made the calorie as the unit of measurement for the energy content of food—a unit that still dominates our thinking about food in the United States today. 

Atwater's work built on more than a century of scientific approaches to food, health, and nutrition that emerged in Europe and the United States. What we now call nutrition science started with a guinea pig. In the early 1780s, French chemist Antoine Lavoisier put the animal inside a chamber, and surrounded it with ice. This experimental apparatus (also called a calorimeter) was designed to measure the amount of heat the guinea pig produced inside. As the animal generated heat in the central chamber, the ice melted. Lavoisier collected and measured the amount of melted water, calculated the heat needed to cause that volume of melting, and compared it to the heat of a burning candle. He speculated that respiration (the act of breathing) is a form of combustion (the process of burning something). Material in the guinea pig’s body was being consumed to generate the heat that melted the ice.

In the following decades, scientists used laboratory methods to understand metabolism and to determine the minimum amount of food humans and animals need to survive. They classified foods into the now-familiar categories of fats, carbohydrates, and proteins. They came to understand the usefulness of variety in a diet. 

Food and diet were becoming more scientific for several reasons. One was the battlefield. During the French Revolution, troops suffered from malnutrition and food poisoning. In 1795, French authorities announced a contest to find a method of preserving food that would increase its availability for the military. Nicolas Appert—a chef with experience in fermenting, distilling, and preserving—took up the challenge. Drawing on existing methods of tightly sealing food in containers and heating them, he developed a method for canning food at a large scale to meet the needs of armies and growing populations.

And across both Europe and the United States in the 1800s, large numbers of people left farms and small shops to work in the mills and factories of growing cities. New technologies such as the steam engine and, later, electricity increased the size and speed of manufacturing. Growing transportation networks of railroads and canals made it easier to move people and goods. Populations expanded, too. But so did concern over having enough food to feed those populations and the larger system of production and profit that depended on their labor. Anxieties over food production and growing poverty in European and U.S. cities drove more and more scientific research into food and nutrition.

Standards for Thinking About Food