Role of oxidative stress and antioxidants in daily nutrition and human health

Diet is a complex process that we are just beginning to fully understand. We need to develop a deeper comprehension of metabolism, energy balance, the molecular pathways involved in cellular stress response and survival, gut microflora genetics, enzymatic polymorphism within the human population, and the role of plant-derived polyphenols in this context. Metabolic syndrome, encompassing pathologies with a relatively high morbidity, such as type 2 diabetes, obesity, and cardiovascular disease, is a key concern in terms of how daily dietary habits should promote health and prevent metabolic impairments to prevent hospitalization and the need for health care. From a clinical point of view, very few papers deal with this concern; most of the evidence reported focuses instead on in vitro and animal models targeting the activity of phytochemicals contained in the daily diet. A fundamental issue addressed by dietitians deals with the role exerted by redox-derived reactive species. Most plant polyphenols act as antioxidants, but recent evidence supports the idea that these compounds primarily activate a mild oxidative stress to elicit a positive, beneficial response from cells. How these compounds may act upon the detoxifying system exerting a scavenging role from reactive oxygen or nitrogen species is still a matter of debate; however, it can be argued that their role is even more complex than expected-that they act as signaling molecules in the cross-talk mitochondria-endoplasmic reticulum and in enzymatic pathways involved in the energetic balance. In this relationship, a fundamental role is played by the brain-adipose tissue-gut axis. The aim of this review is to elucidate this topic, to present the state of the art with regard to the role of reactive species in cell signaling and the function of metabolism and survival, and to reappraise the role of plant-derived chemicals.