Following the discovery of vitamins in the 1910s, nutritional deficiencies began to be increasingly identified as crucial factors in disease causation. This development partly inspired many colonial doctors and scientists who moved into the Nigerian area and other colonial territories during the interwar years to undertake ethnographic and biochemical dietetic studies in relation to locally prevalent health problems. Fundamentally, these “colonial experts” pathologised tropical diets as lacking in essential nutrients, especially protein. Impelled by their works, the colonial government launched various initiatives to “improve” and “modernise” local diets to achieve the “promotion of public health” and “native welfare”. On the strength of a close reading of germane archival data, this article explores the development of nutrition science and the colonial discovery of animal-protein malnutrition in twentieth-century Nigeria.