Red wine is difficult to study scientifically because it is a highly complex mixture of chemical compounds, that changes composition over time and which shows variety between different wine types. However, generally research investigating the effects of red wine have found important health benefits that are consistent with wine drinkers. In particular red wine is beneficial to the cardiovascular system, and it is clear that some of this benefit derives from the ethanol content of the drink. However, additional benefits may be caused by the presence of a highly complex mixture of polyphenols within the wine that reflect the original polyphenol content of the grapes. Polyphenol research has focussed primarily on the ability of compounds such as flavonoids to decrease oxidative stress in plasma once absorbed. However, a small number of studies have investigated the effects of polyphenols in the gut prior to absorption.
For example, one group of researchers1 investigated the effects of red wine polyphenols on the growth of bacterial populations present in the healthy gut. Following a wash-out period, subjects consumed red wine, de-alcoholised red wine or gin for 20 days each, in a random order. Faecal DNA was analysed using real-time polymerase chain reaction (PCR) and gradient gel electrophoresis. The treatments had differing effects on the dominant population of gut bacteria in the subjects. This is likely a result of a combination of the conditions present in the gut caused by the dietary components and the sources of energy available to the different bacteria for metabolism. Because red wine, de-alcoholised red wine and gin all had different effects of gut bacteria population numbers, this suggests that that bacteria in the gut are altered differently by ethanol intake when compared to polyphenol intake.
Analysis of the urine of the subjects also showed that phase II conjugates of resveratrol, a known beneficial stilbene polyphenol in red wine, were increased in the urine following wine consumption, but not following gin consumption. This suggests that wine polyphenols are absorbed and metabolised in humans, as has been previously reported. Concentrations of dihydroresveratrol, a product of bacterial metabolism, was also increased following wine consumption. Interestingly the resveratrol metabolite concentrations in urine were significantly higher following de-alcoholised red wine, when compared to red wine. These results also support previous evidence to suggest that polyphenols are rapidly and extensively metabolised in humans and that parent aglycone polyphenols are rarely detected in plasma or urine of humans. The polyphenol composition of the red wine and the de-alcoholised red wine were similar, but minor differences were likely due to the processing to remove the alcohol.
The different treatments also had other physiological effects on the subjects. Both red wine and de-alcoholised red wine significantly decreased the systolic blood pressure of the subjects, whereas red wine significantly decreased the diastolic blood pressure. Therefore red wine appears to have favourable effects on blood pressure, which might be another mechanisms by which alcohol intake is protective of cardiovascular disease. Red wine and de-alcoholised red wine also caused a significant decrease in C-reactive protein, a marker of systemic inflammation, perhaps due to the increased plasma concentrations of polyphenols. Fasting triglyceride and total cholesterol concentrations also decreased after both wine treatments, which is consistent with other studies. However there was a decrease in high density lipoprotein (HDL). Associations are known to exist between certain gut bacteria and plasma cholesterol concentrations, but the cause and effects are not fully understood.
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