(diet-related diseases develop over time) which would otherwise burden subjects and be expensive in Experimental studies. In nutritional epidemiology, Experimental studies may be used to draw causal conclusions between dietary exposures and health outcomes, however for some diet-disease relations there are ethical considerations. Nutritional policy and procedure decisions are therefore guided by findings from a combination of sources to ensure accuracy, reliability and validity. The measure of exposure is dependent on the question and study design. It can be objectively or subjectively measured on individuals or populations in the past or present. In nutritional epidemiological studies this refers to factors such as food including nutrients and non-nutrients and the social environment. The effect of these exposures is measured as outcomes. In nutritional epidemiological the outcome is commonly referred to as the disease state or the anthropometric or physiological state under either continuous or discrete variables. The objective of nutritional epidemiological research is to provide scientific evidence to support an understanding of the role of nutrition on the causes and prevention of ill health. It is important to address the factors that affect food supply, including quality, quantity and balance and the factors that affect food after consumption. The development of a specific, feasible and relevant aim of study and target population is the first step in epidemiological research. The second step is the selection and correct use of a method that measures exposure and outcome followed by extensive analysis. Exposure and outcome of interest are measured to enable reliability of the relationship assessed. Studies that are well designed, have a strong foundation, detailed methodology and are governed by ethical principles will have the derived conclusions used to improve health care. All steps require knowledge of past and current literature. The different nutritional epidemiological study designs offer advantages and limitations in different circumstances. Ecological study An ecological study is an observational study that studies risk-modifying factors on health outcomes of populations based on their geographical and/or temporal ecological state. Ecological studies are useful in studying patterns of disease in large populations however may not accurately reflect true associations between individuals within those large populations. Ecological studies use geographical information to examine spatial framework of disease and exposure but there is potential for systemic difference in classification language. Cross-sectional study A cross-sectional study is an observational-individual study that measures exposure and outcome in the present. In examining the relationship between disease and