Received date: December 17, 2012; Accepted date: December 18, 2012; Published date: December 20, 2012
Citation: Celep GS, Rastmanesh R (2013) Polyphenol Consumption and Metabolic Diseases. J Nutr Disorders Ther 3:e106. doi:10.4172/2161-0509.1000e106
Copyright: © 2013 Celep GS, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Polyphenols are regular components of human diet and are associated with several beneficial health effects . Many polyphenols have been identified in plants which are classified as flavonoids, phenolic acids, stilbenes and lignans depending on their chemical structures . They possess several biological activities including antioxidant, antibacterial, antiviral, immunomodulatory, antiinflammatory, antiallergic, antimutagenic, antiviral, antineoplastic, antithrombotic, and vasodilatory activities [3,4]. The most prominent activity of polyphenols is expressed to be their antioxidant activities againts oxidative stress related with their ability to scavenge hydroxyl radicals, superoxide anions, and lipid peroxy radicals [5,6].
The main sources of polyphenols in the diet are fruits and beverages such as tea, coffee and wine . Chocolate with its high flavonoids content [7,8] along with vegetables, cereals and legume seeds also contribute to polyphenol intake.The total daily intake of polyphenols is estimated to be around 150-1000 mg [9,10].
Polyphenols have an enormous variability in their structure, consequently in their function. Currently, more than 8000 phenolic structures have been identified in plants . They usually occur as glycosides in the plants .
Among the common polyphenols in human diet, quercetin, kaempferol, myricetin and isorhamnetin are present in onions, apples, and tea [12,13]. Apigenin and luteolin can be found in celery, parsley, and artichoke in high amounts . Catechins and procyanidins are found in red wine, grapes, tea and cocoa. Naringenin and hesperetin are the common polyphenols of citrus fruits. Anthocyanins are also important dietary flavonoids. Resveratrol (3,5,4 u-trihydroxystilbene) can be found in grapes, peanuts and also in berries, red cabbage and spinach .
Epidemiological studies have revealed that there are strong associations between the consumption of polyphenols and prevention of certain metabolic diseases. Oxidative damage is implicated in a number of diseases including cancer, cardiovascular and neurodegenerative diseases and polyphenols act in these cases as antioxidants with different mechanisms of actions. The role of free radicals, including the superoxide radical (O2−), hydroxyl radical (.OH), hydrogen peroxide (H2O2), and lipid peroxide radicals have been implicated in cancer , cardiovascular disease [7,8], diabetes , gastrointestinal inflammatory diseases , liver disease , and also in aging [20,4].
Catechin and its derivatives, oligomeric proanthocyanidins, quercetin and quercetin chalcone, ginkgo polyphenols, silymarin, and others can be utilized in preventative and treatment protocols for cardiovascular disease, cancer, and liver diseases . Regular consumption of isoflavones such as genistein found in soy reduced arteriosclerosis and certain cancers since they have the capability to act as phytoestrogens .
The prevalence of obesity and related metabolic complications with morbidity has increased dramatically in recent years . Diabetes and obesity are major risk factors for cardiovascular diseases, several forms of cancer (such as colon and prostate) and metabolic diseases [23,24]. High polyphenol and selectively-restricted probiotic diet is proposed as a regimen by nutritionists for maintaining normal body weight  and this type of diet has attracted great attention recently.
The anti-obesity effect of green tea catechins is particularly attributed to Epigallocatechin Gallate (EGCG), which exhibits its antiobesity effects through suppression of adipocyte differentiation and proliferation, inhibition of fat absorption from the gut, and suppression of catechol-o-methyltransferase (COMT) enzyme that inhibits fatty acid oxidation in brown adipose tissue .
The administration of purified anthocyanins from blueberries were reported to lower serum triglycerides, cholesterol and leptin levels. Different mechanisms were suggested to explain the effects of polyphenols on the lipid metabolism however the exact mechanisms are still unknown .
Dietary polyphenols, have antioxidant and anti-inflammatory properties via modulating different pathways, such as NF-κB- , mitogen activated protein kinase-dependent signaling pathways and thereby regulating metabolism, stress resistance, cellular survival, cellular senescence/aging, inflammation-immune function. Resveratrol has been suggested to increase glucose uptake through up-regulation of estrogen receptor-α, and increase GLUT 4 expression through phosphatidylinositol-3 kinase and AKT pathway. Through up-regulation of SIRT 1, resveratrol is denoted to help mitochondrial biogenesis, oxidative phosphorylation, and suppress lipid accumulation [28,29].
Inflammation is a free radical involved process. The enzymes cyclooxygenase and lipoxygenase which oxidize arachidonic acid in cell membranes form potent pro-inflammatory metabolites, including prostaglandins, leukotrienes, and thromboxanes. Polyphenols quercetin, rutin, kaempferol, curcumin, and silymarin exhibit inhibition of cyclooxygenase and lipoxygenase in vitro [30-32]. In addition, polyphenols can induce antioxidant enzymes such as glutathione peroxidase, catalase and superoxide dismutase which protect the cells by decomposing hydroperoxides, hydrogen peroxide and superoxide anions, respectively. They can also inhibit the expression of enzymes such as xanthine oxidase [33,34].
Polyphenols can also contribute to health by inhibiting the platelet aggregation where the 3,4-dihydroxyphenylacetic and 4-hydroxyphenylacetic acid metabolites were found to be more active than their precursors rutin or quercetin .
Polyphenols concentrations in plasma are low as usually less than 1 μmol/L in part because of rapid metabolism by human tissues  so the activities of the metabolites gain important attention to reveal the beneficial effects of polyphenols. Understanding the mechanisms of actions of polyphenols and their metabolites either as antioxidants or modulators of cell signaling will help to evaluate the modulators in metabolic diseases [36,37]. The metabolites formed in the small intestine and hepatic cells, and low molecular weight catabolic products produced by the colonic microflora carries critical interest for drug discovery and also for dietary prevention of disease including metabolic diseases .
It is important to unravel the complex biological activities of polyphenols and their metabolites using in vitro and in vivo studies to better understand their benefits for human health.