Sitology is the scientific study of food, diet, and nutrition in relation to health, an older term for what is now usually called nutritional science. It covers the composition of foods, the physiology of digestion and metabolism, and the links between dietary patterns and disease. The word fell out of fashion as the field professionalised into nutrition and dietetics, but it captures the original ambition: a single science of eating and health. Modern sitology, under its newer names, spans biochemistry, epidemiology, and public health, from the molecular fate of a fatty acid to the dietary patterns of whole populations. Whatever the label, the questions are unchanged: what should humans eat, and why.