nutrients are the primary dietary component that are of interest in studying the diet-disease relationships because they give us more direct biological mechanisms. however, exploring the associations of the foods of food groups with disease occurrence could also give us an important information in the causal relationships between diet and diseases. when there are no specific nutrient that was shown to be related to a disease, a relationship between a certain food and the disease could provide a now hypothesis for the responsible components. if an association exists with both the overall intake of a nutrient and more than one food source of that nutrient, it is more likely that the association is causal. on the other hand, foods with similar nutrient components could have different effects on our body due to a complex interaction between the nutrients within the food. epidemiologists should employ both approach (nutrient and food) in order to have an unbiased assessment for the association between diet and diseases. we will take an example of a cohort study which looked at the association between dairy products, calcium, and vitamin D and the risk of breast cancer.