McCarrison is credited with being the first to experimentally demonstrate the effect of deficient dietaries upon animal tissues and organs. He also carries out human experiments aimed at identifying the cause of goitre, and includes himself as one of the experimental subjects. Much of his work is pioneering. His 1921 book Studies in Deficiency Disease is considered notable at the time, being published at a time when knowledge of vitamins and their role in nutrition is crystallizing.
McCarrison qualifies in Medicine at Queen’s College, Belfast in 1900. At age 23, he goes to India, where he spends 30 years on nutritional problems. His research in India on the cause of goitre wins widespread recognition and in 1913 he is promoted to do research. He attains the rank of major-general in the Indian Medical Service and founds the Nutritional Research Laboratories in Coonoor, where he remains until his retirement from the Indian Medical Service in 1935. After retiring, he returns to England and gives a series of three Cantor lectures on successive Mondays at the Royal Society of Arts, about the influence of diet on health. The first lecture focuses on the processes of nutrition; the second, on food essentials and their relationship to bodily structure and function; the third on disease prevention and physique improvement by attention to diet. The lectures are subsequently published in book form under the title Nutrition and Health, and at the time of the third edition in 1962, are still seen as relevant, with the advances of the preceding 25 years largely filling the details of the principles previously recognised by McCarrison.