The scheme of generating the level of evidence associated with each study according to its study design followed the considerations of the WHO [2] and the evidence-based guidelines for the prevention of nutrition-related diseases of the DGE [3]. Intervention studies were given the highest level of evidence, followed by methodologically well-conducted cohort studies (Table 2). Meta-analyses are rated higher than individual studies among its level. In theory, for deriving the relative risk, case–control studies have similar strength than cohort studies. In practice, however, compared with cohort studies, they have the disadvantage of recall and selection bias. This especially applies to case–control studies in the field of nutrition. Therefore, they are rated with a lower level of evidence than cohort studies. Likewise, cross-sectional studies are allocated with a low level of evidence because their study design does not show a clear temporal connection between the investigated nutritional factor and the disease.