Minot was diagnosed with diabetes mellitus in 1921 at the age of 35, by Dr Elliott P. Joslin, a fellow professor at Harvard Medical School and one of the leading diabetes doctors of his time. Diabetes was a fatal disease at the time. Joslin kept him alive the only way he knew, by restricting food. Minot was 6 feet one inches tall and only weighed 135 pounds. Joslin put him on a diet of only 530 calories per day. Minot, like most every diabetes patient, at the time, would probably die within a year.
However, insulin was discovered at about the same time Minot was diagnosed. Insulin became widely available about a year later. Dr. William Castle observed that Frederick Banting's and Charles Best's discovery of insulin in 1921, not only transformed diabetes treatment, but also, by keeping Minot alive, contributed towards the discovery of a cure for pernicious anemia.