Dietary or nutritional factors are studied in relation to disease occurrence in populations in nutritional epidemiology. Nutritional epidemiology findings frequently contribute to the data used to provide dietary recommendations for cancer and other diseases prevention. For ages, epidemiological methods have been used to investigate the link between diet and disease, with the goal of identifying nutritional deficiencies and identifying foods to alleviate them. Nutritional epidemiology is a subdiscipline of epidemiology that provides nutritional science with particular expertise. It provides information on the diet-disease association, which is then converted into prevention practise through Public Health Nutrition. Diet can be researched at several levels in epidemiological research, including nutrient consumption, foods, food groupings, and/or trends. Directly determining what people eat (e.g., by the administration of questionnaires), quantifying markers of intake in biological specimens, or estimating body size and the relative sizes of body compartments are all ways to measure these exposures.