The proliferation and metastasis of cancer cells accelerate
when immune functions are disturbed. It has been found that
cancer patients have lower NK cell activity than healthy
controls and persons with lower NK cell activity are subject to
higher rates of cancer incidence, metastasis and aggravation of
cancer (127–131). The macrophages infiltrating solid tumor
have less phagocytic activity (132). On the other hand, when
cancer patients ingest foods capable of improving immune
functions, the prognosis becomes much better (133–137).
Based on the reports of clinical trials with cancer patients,
phagocytic activity, NK cell number, T cell number, DTH and
IFN- production are all useful immune parameters for assessing
the effect of foods on prognosis after surgical operation for
cancer (Table 1). Moreover, it has been reported that NK cell
activity deteriorates in AIDS patients (138), and branched
chain amino acids, probiotics and vitamin A improves
virus-triggered diseases (139–141).