Evidence is rapidly accumulating as to the beneficial effects of foods. However, it is not always clear
whether the information is based on data evaluated impartially in a scientific fashion. Human research
into whether foods modulate immune functions in either intervention studies or randomized controlled
trials can be classified into three categories according to the physical state of subjects enrolled for
investigation: (i) studies examining the effect of foods in healthy individuals; (ii) studies analyzing the
effect of foods on patients with hypersensitivity; and (iii) studies checking the effect of foods on
immunocompromized subjects, including patients who had undergone surgical resection of cancer and
newborns. The systematization of reported studies has made it reasonable to conclude that foods are able
to modulate immune functions manifesting as either innate immunity (phagocytic activity, NK cell
activity) or acquired immunity (T cell response, antibody production). Moreover, improvement of
immune functions by foods can normalize the physical state of allergic patients or cancer patients,
and may reduce the risk of diseases in healthy individuals. Therefore, it is valuable to assess the
immune-modulating abilities of foods by measuring at least one parameter of either innate or acquired
immunity.