By the 1930s, it was well known that rats fed a diet of corn – which contains a single protein called “zein” – would eventually die.
Interested in how mammals metabolize food, William C. Rose, a biochemist at the University of Illinois, fed the rodents various combinations of amino acids, the building blocks of proteins necessary for most bodily processes.
The rats still died – until the milk protein “casein” entered their diets. The substance, Rose figured, must contain an unknown amino acid essential for sustaining life. This notion led to Rose’s 1935 discovery of threonine, an amino acid that must be obtained from food.
Over the next two decades, Rose expanded his work to the human diet, modifying the eating habits of male graduate students as a means of identifying the eight essential amino acids required for survival.
The research helped inspire nutrition guidelines and amino acid requirements that are still referenced today.