**4. Conclusion**

by the action of tumor suppressor genes. Tumor suppressor genes act by way of effecting cell division cycle arrest in case of DNA damage that affords DNA repair or cell death. One of the major causes of DNA damage is oxidative stress that emanates from the imbalances between reactive oxygen species (ROSs), known as free radicals and antioxidants. In the case, where DNA damage results in the malfunctioning of tumor suppressor genes, cell division cycle continues even in situations, where it should not of which the result is uncontrolled cell growth. Oxidative DNA damage may also affect metabolism regulatory genes that may lead to inadequate or impaired insulin. As such, oxidative DNA damage may culminate in the development of diseases such as cancer and diabetes mellitus [23]. The continuous supplementing of the human body with antioxidants is an important intervention that contributes immensely to the attainment of a balance between ROSs and antioxidants, which reduces oxidative stress. Consumption of fruits and vegetables contribute to the replenishing of the body with antioxidant as they are sources of phytochemicals with antioxidant properties [24]. Explanation of the molecular basis of diseases such as diabetes and cancer brings forth the understanding that adequate consumption of fruits and vegetables may result in the prevention and reversal of these conditions [18]. In the case of diabetes, high blood glucose levels, complications arise from the accumulation of glycated proteins known as advanced glycation end-products (AGEs). Antioxidation, one of the known major biological activities of phytochemicals is reported to contribute to the prevention of the formations of AGEs [25], as well as having protective effects against AGEs induced in stem cells [26]. As such, the immediate question is what contributes to the escalation of the prevalence of these diseases as well as escalated fatalities they cause, in the midst of massive production of fruits and vegetables that is taking place. The answer to this question may lie in understanding the biosynthesis and accumulation of phytochemicals in fruits and vegetables. The accumulation of phytochemicals in plants parts are reported to be for plants survival or defense mechanism in response to adverse environmental influences. Such environmental influences may include pathogens attacks, competitive co-habitation plant species, insect predation, and herbivorous attack. This exposure to hostile environmental settings mainly occurs in wild set-ups. Plants have been shown to have both qualitative and quantitative differences in their phytochemical compositions when growing under varying conditions [27]. In today's world, crops and plantations are shielded from hostile environmental conditions due to modern agricultural practices that also include the use of insecticides and chemical weed removals (herbicides). While production targets may be improved and attained [10], these modern agricultural practices may lead to the alteration of phytochemical compositions accumulation in agricultural products such as fruits and vegetables. Phytochemical accumulation alterations in plants may creep in since the threat that induces biosynthesis of phytochemicals would have been removed. This alteration in the accumulation of phytochemicals in fruits and vegetables may have adverse effects on human health such as inadequate availability of phytochemicals with antidiabetic and anticancer properties. As such, while production could be optimized through modern agricultural practices the quality of the agricultural produce may be negatively affected in terms of their phytochemical compositions. Thus, caution should be exercised not to erode or negatively alter the phytochemical biosynthesis patterns in fruits and vegetables in pursuit of massive production. Alternatively, agricultural practices could include the creation of condi-

184 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

tions that will induce bioaccumulation of phytochemicals in fruits and vegetables.

Plants products, including fruits and vegetables, generally possess two types of chemicals that play different roles known as primary and secondary metabolites. Secondary metabolites are produced for defense purposes in plants in response to detrimental environmental stimuli and contribute to the well-being of humans upon consumption due to their disease prevention and reversal properties. However, modern agricultural methods, although with improved production yields, may give rise to phytochemical accumulation alterations in agricultural products such as fruits and vegetables that eventually have negative effects on their health benefits in human beings. The extent, to which modern agricultural practices may affect the accumulation of important phytochemicals in fruits and vegetables still needs to be fully determined, which presents scope for future research.
