Hazel Katherine Stiebeling (1896–1989) was an American nutritionist who pioneered the development of USDA programs for nutrition including USDA Recommended Dietary Allowances (RDAs) of vitamins and minerals. Stiebeling made important contributions to the understanding of diet composition, nutritional value of foods, dietary guidelines, and the idea and development of dietary standards. Among her recommendations were eating more milk, fresh fruit, and green vegetables. She also helped to develop plans for disaster relief in the South during the economic hardships of the Great Depression. In 1959, Stiebeling became the first woman to receive the President's Award for Distinguished Federal Civilian Service. In 1964, she was named a Distinguished Fellow of the American Society for Nutrition (DFASN).

Hazel Katherine Stiebeling was born on March 20, 1896, to Adam Stiebeling and Elizabeth Brand on their farm near Haskins, Ohio. Her parents were German immigrants. Hazel was one of six children. Living on a farm is believed to have developed her interest in food and nutrition. She began to study domestic science in high school.

After high school, Stiebeling enrolled in a two year program in domestic science at Skidmore College. She later said she discovered Henry Sherman's book, The Chemistry of Food and Nutrition, in the college's library and was inspired by it. She graduated in Skidmore's class of 1915.

Stiebeling was employed for three years as a schoolteacher before entering the Columbia University Teachers' College. There she was an assistant in Foods and Nutrition, working with Mary Swartz Rose. Stiebeling received a Bachelor's degree in Science from Columbia University in 1919, and a Masters in nutrition in 1924.

Stiebeling then became a research fellow under Henry Sherman at the Graduate School of Columbia University. Her research included in the basal metabolism of women, the effects of vitamin D on the deposition of calcium in bone, the nutritional value of protein in human subjects, and other projects. Stiebeling received her PhD in chemistry from Columbia in 1928. Her thesis was on a method for studying the concentrationf of vitamins A and D in tissues.

In 1930, after graduation from the PhD program, Stiebeling was hired as Head of the Section on Food Economics at the USDA Bureau of Home Economics. The Bureau of Home Economics had been formed in 1923. The Chief of the Food and Nutrition Division was Louise Stanley.

At the Bureau, Stiebeling began an extensive long-term investigation of the nutritional value of diets in the United States. In 1933, Stiebeling and others produced a USDA publication on diet planning in 1933 that was the first known publication to include the term "dietary allowances". Stiebeling called for quantitative benchmarks that could be used to compare the nutritional value of foods with the nutrient needs of the body. This was the first quantitative national dietary standard for the minerals calcium, iron, phosphorus, and vitamins A and C. Values were based on her research in the Sherman laboratory.

Among her tasks at the Bureau, Stiebeling helped to develop emergency plans to provide food to those suffering from serious droughts in the Southern United States during the Great Depression. Stiebeling's work also included the first national survey of consumer purchasing in the USA, carried out in 1935–36. President Franklin D. Roosevelt summarized the results of the study when he stated in his second inaugural address on January 20, 1937 that “I see one-third of a nation ill-housed, ill-clad, ill-nourished.”