This paper examines the activities of Saiki Tadasu, a leading Japanese nutrition scientist of the early twentieth century. According to his American counterpart, Dr. Victor G. Heiser, Saiki's work was "of great benefit to the human race." Using a variety of sources in Japanese archives, the Rockefeller Archive Center, and the League of Nations Archives, this paper focuses on Saiki to explore Japan's role in the making of a global science of nutrition, and to map out an international network of intellectual cooperation and knowledge circulation on nutrition science during this period. Inspired by the work of Iris Borowy and Tomoko Akami, it illustrates a world of scientific knowledge-sharing about human well-being which extended geographically beyond the Atlantic world, and thematically beyond disease control. Following Saiki's lead, from 1900 to 1927, Japanese nutrition scientists contributed to growing public recognition of the importance of nutrition science and championed its global development.