Polyphenols are a large heterogeneous group of secondary plant metabolites. Polyphenols are likely involved in plant defences against pathogens and environmental stresses such as protection from pollution and ultraviolet light. The ability of polyphenolic compounds to protect plants from environmental stress relates to their antioxidant capacity. Generally the presence of hydroxyl groups confers reducing power to the structures, and the multiple phenolic rings allows the charge from unpaired electrons to be dissociated over the entire structure, reducing the reactive effects of any lone pairs of electrons. In this way polyphenols are able to break free radical chain reactions and limit the oxidative stress that occurs in plants. Polyphenols are bioavailable in humans and evidence shows that they possess antioxidant ability in humans. A growing body of evidence supports the contention that polyphenols are beneficial to the health because of the antioxidant potential they possess in human tissues.
Fruits, vegetables and herbs are rich in polyphenols, and this may explain some of their health effects. Studies show that those who eat higher amounts of polyphenols containing foods such as tea, wine and chocolate are protected from disease, particularly cancer and cardiovascular disease. The protective effects of polyphenols against cardiovascular disease are most evident in those with detrimentally altered cardiometabolic profiles. In particular, polyphenols may be able to improve altered lipoprotein profiles and reduce high levels of oxidative stress, both of which are associated with an increased risk of cardiovascular disease. Long chain marine omega 3 (n-3) fatty acids are also beneficial at improving cardiometabolic risk profiles and evidence suggests that combinations of long chain fish oils and polyphenols may have synergistic effects at reducing the risk of cardiovascular disease. Researchers have therefore investigated the effects of polyphenols and long chain fish oils in those at high risk of cardiovascular disease.
For example, in one study, researchers1, administered a similar isoenergetic diet that was either poor in polyphenols and fish oils, rich in fish oils, rich in polyphenols, or rich in fish oils and polyphenols. Subjects who were obese and at high risk of cardiovascular disease followed the diet for 8 weeks. Using such a 2 x 2 study design allowed the researchers to assess the individual effects of the polyphenols and the fish oil in the subjects. Polyphenols were effective at reducing the fasting and postprandial very low density lipoprotein (VLDL: also sometimes called triglyceride) levels. Fish oils were effective at reducing the postprandial chylomicron cholesterol and VLDL apolipoprotein B-48 (one of the primary apoproteins in chylomicrons along with apolipoprotein B-100). The urinary marker of oxidative stress, 8-isoprostane also decreased significantly in the polyphenol groups. The changes in the lipoprotein profiles of the subjects correlated significantly with changes to the 8-isoprostane levels.
These results suggest that diets rich in polyphenols decrease oxidative stress and improve the fasting and postprandial triglyceride levels of subjects at high risk of cardiovascular disease. The effects of the fish oils were less certain as it is unclear if reductions in postprandial chylomicron cholesterol is protective of cardiovascular disease. However, many studies have shown benefits of fish oil supplementation in terms of reducing fasting triglyceride levels in humans. However of more significance was the fact that the subjects in the fish oil group lost weight, despite being administered an isoenergetic diet. Therefore these results support previous studies that show that fish oils have weight loss effects and these effects do not require energy restriction. The sources of polyphenols in this study included whole foods such as blueberry jam, dark chocolate, artichokes, onions, spinach, rocket, green tea, coffee and extra virgin olive oil. The main sources of fish oils were fish including salmon, dentex and anchovies.
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