Nutritional epidemiology focuses on an understanding of the relationship between diet and disease risk. The assessment of dietary and nutritional exposure is a complex methodological challenge. Traditionally, diet evaluations have been made by means of dietary data, such as 24-h recalls and food frequency or diet history questionnaires. However, all of these methods have some inherent weaknesses or limitations due to the limited accuracy in measuring the intake of food, nutrients or phytochemicals. Nowadays, nutritional biomarkers have become an attractive alternative approach. According to conventional definition...