Interpreting epidemiologic studies of diet-disease relationships

The purpose of this paper is to examine key issues in the interpretation of nutritional epidemiologic study results when the focus is on major chronic degenerative diseases of multifactorial etiology. The estimation of disease risk associated with a particular dietary factor is influenced by the presence of other risk factors within the study population, complicating the interpretation of relative risk and odds ratio estimates in this context. Identifying the precise role(s) that dietary factors play in the onset or progression of chronic diseases is further complicated by the intercorrelation of dietary components and by the correlation of dietary patterns with other behavioral and environmental factors which may also impart or exacerbate risk of disease. Issues of study design and measurement make it difficult to identify relationships in nutritional epidemiology, but also thwart the rejection of hypotheses regarding diet-disease relationships when studies fail to yield significant associations. In drawing causal inferences from epidemiologic findings, it is important to examine evidence from a variety of sources and to look for congruence between epidemiologic, clinical and laboratory research findings.