Current evidence supports a contribution of polyphenols to the prevention of cardiovascular disease, but their mechanisms of action are not understood. We investigated the impact of red wine polyphenols on postprandial cytotoxic lipid peroxidation products (MDA) levels in humans. In a randomized, crossover study, the effect of red wine polyphenols on postprandial levels of plasma and urine MDA was investigated. Three meals of 250 g turkey cutlets supplemented by water (A); soaked in red wine after heating plus 200 ml of red wine (B); or soaked in red wine prior to heating plus 200 ml of red wine (C) were administered to 10 healthy volunteers. Subject baseline plasma levels of MDA were 50 +/- 20 nM. After a meal of turkey meat cutlets, plasma MDA levels increased by 160 nM (P<0.0001); after (B) there was a 75% reduction in the absorption of MDA (P<0.0001). However, after (C), the elevation of plasma MDA was completely prevented (P<0.0001). Similar results were obtained for MDA accumulation in urine. Our study suggests that red wine polyphenols exert a beneficial effect by the novel new function, absorption inhibition of the lipotoxin MDA. These findings explain the potentially harmful effects of oxidized fats found in foods and the important benefit of dietary polyphenols in the meal.

The Western diet contains large quantities of oxidized lipids, because a large proportion of the food in the diet is consumed in a fried, heated, processed, or stored form. We investigated the reaction that could occur in the acidic pH of the stomach and accelerate the generation of lipid hydroperoxides and cooxidation of dietary vitamins. To estimate the oxygen content in the stomach after food consumption, oxygen released from masticated bread (20 g) into deoxygenated water (100 mL) was measured. Under these conditions, the oxygen concentration rose by 250 microM and reached a full oxygen saturation. The present study demonstrated that heated red meat homogenized in human gastric fluid, at pH 3.0, generated hydroperoxides and malondialdehyde. The cross-reaction between free radicals produced during this reaction cooxidized vitamin E, beta-carotene, and vitamin C. Both lipid peroxidation and cooxidation of vitamin E and beta-carotene were inhibited at pH 3.0 by red wine polyphenols. Ascorbic acid (44 mg) at a concentration that represented the amount that could be ingested during a meal inhibited lipid peroxidation only slightly. Red wine polyphenols failed to prevent ascorbic acid oxidation significantly but, in conjunction with ascorbic acid, did inhibit lipid peroxidation. In the presence of catechin, a well-known polyphenol found in red wine, ascorbic acid at pH 3.0 works in a synergistic manner preventing lipid peroxidation and beta-carotene cooxidation. The present data may explain the major benefits to our health and the crucial role of consuming food products rich in dietary antioxidants such as fruits, vegetables, red wines, or green tea during the meal.

To determine the stomach bioreactor capability for food oxidation or antioxidation, rats were fed red turkey meat cutlets (meal A) or red turkey meat cutlets and red wine concentrate (meal B). The hydroperoxides (LOOH) and malondialdehyde (MDA) levels of the stomach contents were evaluated during and after digestion; the postprandial plasma MDA level was also evaluated. In independently fed rats, the stomach LOOH concentration fell substantially 90 min following the meal, and the addition of red wine polyphenols enhanced LOOH reduction 3-fold. A similar trend was obtained for MDA. After pyloric ligation, the stomach contents of rats fed red meat homogenate showed >2-fold increases in LOOH and MDA accumulation. The postprandial plasma MDA level increased significantly by 50% following meal A and was maintained or even fell by 34% below basal level following meal B. The findings show that consumption of partially oxidized food could increase lipid peroxidation in the stomach and the absorption of cytotoxic lipid peroxidation products into the body. The addition of antioxidants such as red wine polyphenols to the meal may alter these outcomes. These findings explain the potentially harmful effects of oxidized fats in foods and the important benefit of consuming dietary polyphenols during the meal.

Recent studies dramatically showed that the removal of circulating modified low-density lipoprotein (LDL) results in complete prevention of atherosclerosis. The gastrointestinal tract is constantly exposed to food, some of it containing oxidized compounds. Lipid oxidation in the stomach was demonstrated by ingesting heated red meat in rats. Red wine polyphenols added to the rats' meat diet prevented lipid peroxidation in the stomach and absorption of malondialdehyde (MDA) in rat plasma. In humans, postprandial plasma MDA levels rose by 3-fold after a meal of red meat cutlets. MDA derived from meat consumption caused postprandial plasma LDL modification in human. The levels of plasma MDA showed a 75% reduction by consumption of red wine polyphenols during the meat meal. Locating the main biological site of action of polyphenols in the stomach led to a revision in the understanding of how antioxidants work in vivo and may help to elucidate the mechanism involved in the protective effects of polyphenols in human health.

The antioxidant capability of coffee polyphenols to inhibit red-meat lipid peroxidation in stomach medium and absorption into blood of malondialdehyde (MDA) in humans was studied. Roasted-ground coffee polyphenols that were found to inhibit lipid peroxidation in stomach medium are 2- to 5-fold more efficient antioxidant than those found in instant coffee. Human plasma from ten volunteers analyzed after a meal of red-meat cutlets (250 g) revealed a rapid accumulation of MDA. The accumulation of MDA in human plasma modified low-density lipoprotein is known to trigger atherogenesis. Consumption of 200 mL roasted coffee by ten volunteers during a meal of red-meat cutlets, resulted after 2 and 4 h in the inhibition by 80 and 50%, respectively, of postprandial plasma MDA absorption. The results obtained in vitro simulated stomach model on MDA accumulation were predictive for the amount of MDA absorbed into circulating human plasma, in vivo. Timing the consumption of coffee during the meals may make it a very active functional food.