Linking nutrition deficiency and disease
While Dr. McCarrison was preoccupied with caring for hundreds of British and Indian troops in the Himalayas, he found time to record his observations on the Hunza people, particularly what they ate and on their overall health.
The Hunzas' good health made an impression on the young doctor. He found other villagers in the Himalayas had a high incidence of thyroid goiter. After running multiple experiments on rats and people (even himself), Dr. McCarrison discovered that goiter disease was caused by a diet lacking in iodine.
After McCarrison gained worldwide acclaim for his work on nutrition deficiency and disease in 1913, his superiors allowed him to conduct research. (Incidentally, McCarrison’s discovery of the role of iodine deficiency and thyroid disease led governments to require our table salt be fortified with iodine.)
For the next several years, McCarrison found regions throughout India where a particular disease was prevalent, and then set down to figure out what nutrition deficiency was causing the disease.