Maintenance of redox homeostasis plays a central role in health and disease prevention, and antioxidant foods are thought to exert protective effects by counteracting oxidative stress. The term “dietaryantioxidant” implies a classical reducing or radical-scavenging capacity, but more data on the in vivo bioactivity of such compounds are needed. Indeed, several dietary antioxidants activate signaling cascadesthat lead to effects that extend beyond radical scavenging, such as the induction of endogenouscyto protective mechanisms and detoxification. Currently, the overall uptake of antioxidants with diet exceedsactual needs, as food additives that include vitamins, colorants, flavoring agents, and preservatives areoften also relatively strong antioxidants. Chronic antioxidative stress favors adverse effects, such as thesuppression of T helper (Th) type 1 immune responses and consequent activation of Th2 reactions thatsupport the development of asthma, allergies, and obesity. In this context, we discuss the immunoregulatorypathway of tryptophan breakdown by enzyme indoleamine 2,3-dioxygenase (IDO), which represents acentral regulatory hub for immune, metabolic, and neuroendocrine processes. Activation of IDO mediated tryptophan metabolism is strongly redox-sensitive and is therefore susceptible to modulationby dietary components, phytochemicals, preservatives, and drugs.© 2
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