Wilbur Olin Atwater (May 3, 1844 – September 22, 1907) was an American chemist known for his studies of human nutrition and metabolism, and is considered the father of modern nutrition research and education. He is credited with developing the Atwater system, which laid the groundwork for nutrition science in the United States and inspired modern Olympic nutrition.

Atwater was director of the first United States Agricultural Experiment Station at Wesleyan University in Middletown, Connecticut and he was the U.S. Department of Agriculture's first chief of nutrition investigations.

Atwater was born in Johnsburg, New York, the son of William Warren Atwater, a Methodist Episcopal minister, temperance advocate, and librarian of Yale Law School and Eliza (Barnes) Atwater. He grew up in, and spent much of his life in New England. He opted not to fight in the American Civil War, instead pursuing his undergraduate education, first at the University of Vermont and then moving to Wesleyan University in Connecticut, where he would complete his general education in 1865. For the next three years, Atwater was a teacher at various schools and in 1868, he enrolled in Yale University's Sheffield Scientific School, where he studied agricultural chemistry under William Henry Brewer and Samuel William Johnson. During his time at Yale, Atwater worked part time as Johnson's assistant analyzing fertilizers for specific mineral content; he also performed the first chemical analysis of food or feed in the United States. Atwater received his doctorate in 1869 in agricultural chemistry, his thesis was entitled The Proximate Composition of Several Types of American Maize, in it he used variations of the proximate analysis system to analyze four varieties of corn. Afterwards, he continued his education for the next two years in Leipzig and Berlin, studying physiological chemistry and acquainting himself with the agricultural experiment stations of Europe. During his time there, Atwater studied under German physiologist and dietitian, Carl von Voit and worked alongside Voit's student, Max Rubner. Atwater spent time traveling throughout Scotland, Rome, and Naples; on his trip he wrote articles about his observations for local newspapers based in the places he had lived in the United States. In 1871, Atwater returned to the United States to teach chemistry at East Tennessee University and the next year moved to Maine State College.

While there, Atwater met Marcia Woodard (1851–1932) of Bangor, Maine, the daughter of Abram Woodard. They married in 1874 and had two children: their daughter Helen in 1876 and their son Charles in 1885.

Wilbur Atwater returned to Wesleyan as a professor of chemistry in 1873 and remained there until his death in 1907. Both he, and his mentor from Yale, Samuel Johnson, were proponents of bringing organizations to the United States similar to the agricultural experiment stations they saw in Europe. Atwater even described the German agricultural experiment stations in an 1875 report to the Department of Agriculture. To persuade the Connecticut legislature to appropriate money for a station, Orange Judd donated funds and Wesleyan offered laboratory facilities and Atwater's services on a part-time basis. Through their work and a $5,600 contribution from the Connecticut legislature for a two-year trial period, the first agricultural experiment station was created in the United States.

Atwater served as administrator of the trial run from 1875 until 1877 with initial research focused on fertilizers. Before the two-year trial was over, the Connecticut legislature agreed to regular funding of the station but had decided to move the permanent Connecticut Experiment Station to the Sheffield Scientific School at Yale with Samuel Johnson as first director. During this time, Atwater wrote numerous articles for scientific periodicals detailing his research and findings in physiological and agricultural chemistry and on research being conducted abroad (specifically in Germany). Many of his articles appeared in a column called "Science Applied to Farming", mostly discussing agricultural fertilizers in Orange Judd's American Agriculturalist.

During the initial phase of the first experiment station, Atwater expanded his fertilizer program and began to study and experiment with the growth and composition of field crops. The field crop research continued even after the appropriation ceased on a nearby farm; Atwater became particularly interested in plant metabolism and was one of the first researchers to provide proof that legumes assimilate nitrogen from the air.

As his experiments and accomplishments became known, Atwater's assistance was requested for a variety of projects. From 1879 to 1882, he conducted extensive human food studies on behalf of the United States Fish Commission and Smithsonian Institution. In 1879, the U.S. Fish Commission offered Atwater funds to study the composition and nutritional value of North American species of fish and invertebrates. For the 1882–1883 school year, Atwater took a leave of absence from Wesleyan to study the digestibility of lean fish with Carl von Voit in Germany. Together, they found fish comparable to lean beef; during this time he became aware of how German scientists were studying nutrition and hoped to bring similar research to the United States upon his return. In 1885, Atwater's first series of studies on peas grown in nutrient solution were published in the American Chemical Journal. That same year, the Massachusetts Bureau of Statistics of Labor requested a study of data that had been collected by the bureau concerning family food purchases. In the study, Atwater calculated the daily per capita supplies of carbohydrates, fat, and protein provided within the data, and taking into account the included cost data, made recommendations on how more economical diets, while still having adequate nutritional value, could be chosen. The report he prepared was included in the Bureau's 1886 Annual Report.