Joslin was involved for seven decades in most aspects of diabetes investigation and treatment, save for the fact that he did not discover insulin.

After graduating from Yale, Elliott Joslin extended his time at the university by enrolling in a master's degree in physiological chemistry.

His carefully assembled data from his medical ledgers eventually allowed him to predict a global diabetes epidemic that is evident today.

In 1908, in conjunction with physiologist Francis G. Benedict, Joslin carried out extensive metabolic balance studies examining fasting and feeding in patients with varying severities of diabetes.

The first hospital blood glucose monitoring system for pre-meal testing was developed under Joslin's direction before 1940 and was the forerunner of the modern glucometer era.

Just after WWII, he expressed concern to the Surgeon General of the U.S. Public Health Service that diabetes was an epidemic, and challenged the government to do a study in his hometown, Oxford, Massachusetts.

The study was started in 1946 and soon confirmed the true incidence of diabetes in the general population (including a percentage of cases that went undetected).

Joslin was adamant in his position that good glucose control, achieved through a low-carbohydrate diet, exercise, and frequent testing and insulin adjustment, would prevent complications.

[9] Before the discovery of insulin, Joslin and Frederick Madison Allen promoted fasting and undernutrition to treat diabetic patients.