Lipopolysaccharides (LPS) are signal molecules attached to the outer cell membrane of Gram negative bacteria. It is thought that LPS can be absorbed in humans where they act as endotoxins and cause inflammation and oxidative stress. A link between high concentrations of pathogenic Gram negative bacteria and diseases of inflammation such as metabolic syndrome and cardiovascular disease has been suggested in the nutritional literature. The typical Western diet, characterised by its low quality processed meats, refined carbohydrates and lack of plant foods, has been implicated as a causative factor in the colonisation of the colon by pathogenic strains of Gram negative bacteria. In contrast, consumption of plant foods rich in prebiotic substances such as fructooligosaccharides (FOS) and polyphenols is thought to shift the microbiology of the colon to one containing more beneficial Gram positive bacteria that lack LPS molecules. Gram positive bacterial strains can outcompete the Gram negative strains, thus limiting their pathogenic impact.
Red wine is a complex mixture of many chemicals derived from the original grapes, and the chemistry of wine is so complex that it has not been fully characterised. Red wine is able to modulate gut bacteria because components within the wine act as prebiotics. Researchers have assessed the effects of red wine on LPS production in otherwise healthy middle aged men by comparison of drinking either red wine, dealcoholised red wine or gin for periods of 20 days1. The effects on LPS were assessed by measuring the serum endotoxin and serum LPS binding protein concentrations after each treatment. The results showed that LPS concentrations in the serum did not differ between red wine, dealcoholised red wine or gin, but fell for all treatments compared to baseline readings. However, Bifidobacterium and Prevotella spp increased in the colon in response to the red wine consumption and the colony numbers correlated with LPS concentrations. Therefore red wine may have some beneficial effects of the health of the colon.
It is becoming increasingly clear that some foods are beneficial to the health despite evidence that they may not be absorbed. The thinking behind this suggests that theses food impact either the rate of digestion and thus reduce the glycaemic effects of carbohydrates or they are able to modulate levels of gut bacteria. Some foods such as fibre may be able to perform both functions, as soluble fibre is both able to inhibit glucose absorption and act as a prebiotic to beneficial strains of bacteria in the colon. The polyphenols in red wine, including resveratrol, may also have this dual role, as some evidence suggests that polyphenols may inhibit certain sugar transporters as well as being able to act as prebiotics. Red wine has been shown previously to inhibit the formation of lipid peroxides in the gut and reduce the absorption of potentially toxic molecules to the circulation (here). The results from this study support a role for red wine in gut health, mainly through its prebiotic effects on gut bacteria.
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