In 1928 he became Director of Nutritional Research in India, where he remained until his retirement from the Indian Medical Service in 1935, when he returned to England, settling at Oxford.

[citation needed] McCarrison is credited with being the first to experimentally demonstrate the effect of deficient dietaries upon animal tissues and organs.

[15] After retiring from the Indian Medical Service in 1935,[10] he gave a series of Cantor lectures at the Royal Society of Arts, about the influence of diet on health.

The first lecture focused 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.

[16] The lectures were subsequently published in book form under the title Nutrition and Health, and at the time of the third edition in 1962, were still not seen as "dated", with the advances of the preceding 25 years largely filling the details of the principles previously recognised by McCarrison.

[17] "McCarrison's work on goitre, cretinism, and thyroid, begun in the western Himalayas in 1902, generated scores of scientific publications during the following thirty-five years",[18] While McCarrison's work is often considered the start of serious studies of goitre and cretinism in South Asia, it was preceded by that of Commissioner David Scott at Rangur in north-east India around 1825, and was investigated by Mountford Bramley at Kathmandu in 1832.

[18] In 1918, McCarrison founded the Beri-Beri Enquiry Unit in a single room laboratory at the Pasteur Institute in Conoor, India.

[15][19][20] In 1926, as head of the Deficiency Diseases Inquiry, McCarrison submitted written and oral evidence on malnutrition to the Royal Commission on Agriculture in India.

"A decade later, when the Commission's chairman, Lord Linlithgow, became Viceroy of India he showed a personal interest in nutrition, pushing it to the top of the research agenda.

[26] The society meetings sometimes raise questions with elusive answers, with speakers presenting material based on scanty, often anectdotal data, inviting criticism that it is "a gathering of cranks".

He demonstrated how many common diseases increasingly prevalent in industrial societies were caused simply by diets made defective by extensive food processing, often with the use of chemical additives.

It contains particularly insightful commentary on the contribution of McCarrison at a time of significant change in the existing university and medical institutions of the UK.