How did calorie counting start? The interesting origins of calorie measurement
Wilbur Olin Atwater was the scientist who first introduced the calorie as a unit of energy in food to an American audience. (In a moment, I’ll explain the difference between “calorie” and “calorie.”)
From 1873 through 1907, Atwater taught chemistry at Wesleyan University in Connecticut. His interest in nutrition and metabolism grew over time, particularly following a trip to Munich when he learnt about German procedures for assessing food nutritional content. He was interested in the relationship between chemical energy from food and manual labor because he wanted to ensure that people ate well.
In an article titled “The Potential Energy of Food” [PDF] published in 1887, Atwater defined a calorie as the amount of heat required to increase the temperature of a kilogram of water by one degree Celsius (or a pound of water 4 degrees Fahrenheit). To demonstrate that a unit of heat could also be a unit of mechanical energy, he defined a Calorie as 1.53 foot-tons — the force required to move a ton by one foot.
Wilbur Atwater’s respiration calorimeter (left) was a big copper-lined box in which a human subject could stay for up to 12 days and do tasks such as exercising, relaxing, and eating lunch (right). Wilbur Atwater’s respiration calorimeter (left) was a big copper-lined box in which a human subject could stay for up to 12 days and do tasks such as exercising, relaxing, and eating lunch. Atwater provided the calorie values of numerous items by the pound in his paper, including round, rather lean beef (807); butter (3,691); cow’s milk, both ordinary (308) and skimmed (176); oatmeal (1,830); and turnips (1,830). (139). His calculations were based on his estimates of nutrient, protein, fat, and carbohydrate content of each food, as well as some trials. Although modern calorie counts for these items change slightly from Atwater’s, we still utilize his estimations of 4.1 calories per gram of protein and 9.3 calories per gram of lipids.
A bomb calorimeter was one of the instruments Atwater used in his studies. It monitors the heat released during a reaction and was already widely used at the time. A sample is placed in a bomb, a steel reaction tank that is submerged in water. The sample is ignited by an electric current, and the heat is absorbed by the water bath. At regular intervals, the temperature of the water is monitored.
A breathing calorimeter was also invented by Atwater, along with Wesleyan physicist Edward Rosa and chemist Francis Benedict. It allowed scientists to estimate the calories consumed by a human subject by measuring the person’s oxygen intake, carbon dioxide emission, and the amount of heat produced as a result. The calorimeter was a copper box encased in wood and zinc that was 6 feet high, 4 feet wide, and 7 feet deep (1.8 by 1.4 by 2.1 meters) to help maintain a steady temperature. The individual would be kept in the box for up to 12 days, performing various duties such as lying down and exercising. These researches provide the groundwork for a better knowledge of metabolic rates.
It took decades to define the calorie, and then came the joule.
Calorie was not coined by Atwater. Nicolas Clément, a chemistry professor at the Conservatoire des Arts et Métiers in Paris, is frequently given this honor. Clément wanted a unit of heat for a discussion of how steam engines turn heat into work in 1819 when he was teaching an industrial chemistry course. He came up with the calorie, which he defined as the amount of heat required to increase the temperature of 1 kg of water by 1°C — a concept that Atwater eventually adopted. Clément, on the other hand, was more specific, stating that the temperature was measured between 0 and 1 °C. Clément’s definition was accepted by scientists, and the calorie was included in French physics textbooks.
Two publications of Adolphe Ganot, a French scientist, were among those translated into various languages. Until the early twentieth century, universities in Europe and the United States used popular textbooks. As a result, Clément’s calorie became a part of the English language.
The National Bureau of Standards in the United States designed this steam calorimeter in 1937 to quantify the output of steam power equipment. The instrument’s front has been hacked away to reveal its layers. The National Bureau of Standards in the United States designed this steam calorimeter in 1937 to quantify the output of steam power equipment. The instrument’s front has been hacked away to reveal its layers.
However, another definition of the calorie was circulating at the same time. In 1852, French chemist Pierre Favre and physicist Johann Silbermann defined a calorie as the amount of energy required to increase the temperature of one gram of water by one degree Celsius — a 1,000-fold difference in scale! Favre and Silbermann’s definition was largely accepted by German scientists.
The differing definitions of the calorie prompted French scientist Marcellin Berthelot to propose a distinction in the 1870s. According to Favre and Silbermann, a calorie (with a lowercase c) is a gram-calorie, and a calorie (capitalized) is a kilogram-calorie. The calorie was then dubbed the “little calorie,” and the Calorie was dubbed the “big calorie.” In his landmark work A Manual of Human Physiology, published in 1894, American physician Joseph Raymond recommended dubbing the enormous calorie the kilocalorie, but the term didn’t catch on until years later.
Meanwhile, the British Association for the Advancement of Science was developing a new energy unit called the joule. During his inaugural speech as chairman of the BAAS in 1882, William Siemens proposed the joule. “The discomfort of a unit so wholly arbitrary is sufficiently apparent to justify the introduction of one based on the electro-magnetic system,” Siemens stated, perplexed by the calorie. He defined a joule as the amount of energy dissipated as heat when a one-ampere electric current travels through a one-ohm resistance for one second.
Wilbur Atwater estimated the calorie counts of many foods, including bananas, using a smaller calorimeter. Wilbur Atwater estimated the calorie counts of many foods, including bananas, using a smaller calorimeter. SPECIAL COLLECTIONS OF THE USDA NATIONAL AGRICULTURAL LIBRARY
As a result, Atwater had a variety of heat energy units to choose from while doing his nutritional research on food. Clément’s calorie would have been mentioned in Ganot’s translated textbooks. During his postdoctoral studies in Germany, he would have come across Favre and Silbermann’s calorie. And, being a scientist, he was certainly aware of the suggested joule, albeit Siemens’ definition was not accepted until 1889, at the second International Electrical Congress.
The history of the calorie has been researched by James L. Hargrove of the University of Georgia, and he has a few theories as to why Atwater chose the calorie. It was the sole unit of energy listed in American dictionaries, for one thing. Perhaps more critically, according to Hargrove, the Calorie was on a manageable scale, allowing Atwater to formulate a daily intake recommendation of 2,000 Calories. A daily calorie intake of 2 million, on the other hand, would have been excessive.
When the international scientific community selected the joule as the standard unit of energy in 1948, both the calorie and the calorie were formally rendered obsolete. It was just too confusing to have two separate meanings defined solely by capitalization and orders of magnitude, as Siemens had pointed out. However, in the United States, nutrition labels still report calories, whereas in other nations, values are reported in both kcals and joules.
Steam generators were designed using calorimeters as a guide.
Calories were not only of importance to nutritionists. Electricity consumption was soaring at the turn of the century, and communities across the globe were constructing new power plants. Generators became increasingly sophisticated after the advent of the steam turbine, and boilers ran at higher temperatures and pressures. Engineers required data on their steam equipment badly, but there were no internationally accepted values for water and steam qualities. As a result, they turned to calorimeters, which were designed to measure the work done by steam, as Clément had intended.
Nathan Osborne, Harold Stimson, and Defoe Ginnings worked on this subject at the United States National Bureau of Standards (now the National Institute of Standards and Technology) beginning in 1921 and continuing for almost two decades. The researchers created the beautiful calorimeter depicted above to investigate the heat capacity and heat of vaporization of water at temperatures up to 100 degrees Celsius.
The gadget, which has been hacked away to reveal the innards, worked in the same way that Atwater’s bomb calorimeters did. The water sample was kept in the spherical inner shell. An electric current added energy, and the scientists observed the change in condition. Until the 1960s, their findings influenced the design and evaluation of steam power equipment.
The introduction and refining of electric heaters, resistance thermometers, and thermocouples allowed calorimeters to become a reliable and accurate tool of measurement in thermal research, as Osborne highlighted in his 1925 study “Calorimetry of a Fluid” [PDF].
Calorimeters have been valuable instruments for chemists, physicists, and engineers for almost two centuries, whether estimating the energy in food or the heat capacity of water. It seems only natural to pay homage to the instruments that calculate calories as we begin a new year and many of us take a newfound interest in calories.
