## 4 Discussion
\begin{table}
\begin{tabular}{|p{113.8 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|} \hline
**Study Type** & **Study Sample/Duration** & **Participants** & **Protocol** & **Summary of Results** & **Study Reference** \\ \hline A randomized, placebo-controlled, double-blinded, single-center study. & 66 participants/4 months & Male gender, 30–60 y, and MetS. & Randomized to either resveratrol or placebo treatment. & Urinary derivatives of amino acids, which reflect the synthesis of the gut microbiota, were altered after resveratrol treatment. & [44] \\ \hline Double blind, cross-over, randomized, clinical trial & 30 healthy non-smoking volunteers/3 weeks & Adults/both male and female & Common, virgin, and refined olive oils were sequentially consumed over three periods of 3 weeks. & Reduction in vivo of LDL oxidation and measurement of T and HT in urine. & [45] \\ \hline Double-blind cross-over trial & 43 participants/3 weeks & 20–70 y, 66\% females, 44\% of study participants were overweight and 4\% were obese & 60 mL/day of HPOO (320 mg/kg polyphenols) or LPOO (86 mg/kg polyphenols) for three weeks. & [46] \\ \hline \end{tabular}
\end{table} 
Table 4: _Cont._insulin sensitivity due to the production of GLP-1, [14] which enhances insulin secretion and \(\beta\) cell proliferation in the pancreas [15]. Dyslipidemia is a major risk factor for cardiovascular disease. Atherogenic dyslipidemia presents increased levels of LDL and decreased levels of HDL. In addition, increased levels of TG are associated with increased cardiovascular risk [15]. Multiple studies have indicated that metabolic endotoxemia contributes to atherosclerosis and cardiovascular disease, which is caused by an augmentation of TC and a decrease in HDL. A strategy for controlling dyslipidemia is consuming a diet abundant in dietary fiber, fruits, vegetables, and soluble fibers. Soluble prebiotic fibers bind cholesterol and impede its absorption, increasing the excretion of cholesterol in the feces [15]. In addition, prebiotics interact with the intestinal metabolism of bile acids and reduce cholesterol reabsorption. [11] Prebiotics have a lipid-lowering effect, by increasing the production of SCFA, which inhibits the synthesis of TG and cholesterol [11; 15; 48]. On the other hand, phytochemicals are defined as bioactive non-nutritive plant compounds [53]. Polyphenols are secondary metabolites of plants and represent a great variety of phytochemicals [41; 54; 55; 56; 57]. They are usually found in plant foods, such as coffee, cocoa, olives, fruits (apples, berries), nuts, some vegetables (lettuce, cabbage), wine and tea, and their consumption as part of the regular diet has been linked to a reduction in the risk of chronic diseases [53; 55; 58]. The interaction between polyphenols and microflora is well-documented. Only a very small part of polyphenols is absorbed in the small intestine and the rest (90-95%) reach the colon in elevated concentrations, where they are degraded by gut microbiome before being absorbed [7; 53; 54; 59; 60] and finally excreted in the urine [41]. Dietary polyphenols are metabolized, as previously mentioned, by the microflora, regulating their composition and generating a series of metabolites [5; 7; 12; 53; 59; 61]. Polyphenols prevent weight gain, reduce lipid levels in the circulation and reduce the endotoxemia and systemic inflammation induced by high-fat diets. All these results together indicate that polyphenols may have an important role in the control of obesity and MetS [12; 54]. Although a decreased intake of polyphenols does not cause specific deficiency diseases, adequate intake presents a lot of possible benefits, specifically for chronic diseases [58]. About 8000 structures of polyphenols have been identified [41; 55; 56; 57; 58], which are classified into four main groups as follows:  
(A) Flavonoids. The first and biggest subgroup of polyphenols, with more than 6000 compounds consisting of 7 main subgroups [41; 53; 56];  
(B) Phenolic Acids (e.g., curcumin).