Throughout his career, Atwater had been interested in human nutrition studies; having conducted the studies on behalf of the U.S. Fish Commission and the Smithsonian Institution, he had continued human nutrition research and the Storrs experiment station became known for nutritional studies. He went on to conduct metabolic studies related to the dietary standards, based on observations from his work with Voit, who had used a Rubner
respiration calorimeter to conduct similar experiments on small animals. Together with Charles Ford Langworthy, they compiled a digest of close to 3,600 metabolic experiments as a primer to the research they would conduct. The calorimeter measured human metabolism by analyzing the heat produced by a person performing certain physical activities; in 1896 they began the first of what would accumulate into close to 500 experiments. Through their experiments, they were able to create a system - which became known as the
Atwater system, to measure the energy in units, known as
food calories. Atwater describes the apparatus in an article: "The experiments are made with a man inside a cabinet, or a respiration chamber, as it is called. It is in fact a box of copper incased in walls of zinc and wood. In this chamber he lives—eats, drinks, works, rests, and sleeps. There is a constant supply of fresh air for ventilation. The temperature is kept at the point most agreeable to the occupant. Within the chamber are a small folding cot-bed, a chair, and a table. In the daytime the bed is folded and laid aside, so as to leave room for the man to sit at the table or to walk to and fro. His promenade, however, is limited, the chamber being 7 feet long, 4 feet wide, and 6 feet high. Food and drink are passed into the chamber through an aperture which serves also for the removal of the solid and liquid excretory products, and the passing in and out of toilet materials, books, and other things required for comfort and convenience." His research was informed by the
first law of thermodynamics, taking into account that energy can be transformed but it cannot be created or destroyed, despite the belief at the time that the law only applied to animals because humans were unique. Earlier experiments concerning calorie intake and expenditure had proven that the first law applied to animals and Atwater's findings demonstrated the law applied to humans as well. Through his research, he was able to demonstrate that calories from different sources might affect the body differently and in turn, published tables that compared calories in various foods. Atwater also studied the effect of
alcohol on the body. His findings showed that humans generated heat from alcohol just as they would from carbohydrates. At a time when the
Scientific Temperance Federation and the
Woman's Christian Temperance Union doubted the nutritional value of alcohol, Atwater proved alcohol could be oxidized in the body and used to some extent as fuel. Information gained from Atwater's experiments was used by the liquor trade in the promotion of alcohol, which upset him greatly. Being described as "very prominent in the
temperance movement", Atwater would lecture students on temperance and encouraged abstinence from alcohol. == Death and legacy ==