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Bias is the main problem that should be considered in epidemiologic research. Information bias caused by measurement error and confounding caused by total energy intake are listed as the main biases in nutritional epidemiology and the concept, fact and the methods for adjusting effects of these biases are discussed. The biases which can be caused during the nutritional epidemiologic research process are listed and discussed. The pros and cons of the continuous data and categorical data of the nutrients and the ways how to categorize the data are reviewed. During the analysis of food and nutrient data, multiple comparison and publication bias are prone to be encountered, and these should be considered in interpretation of the results. Understanding of the biases will lead us to make valuable nutritional epidemiologic research and these lead the application of the research results to control the prevalent noncommunicable diseases.