Nutrient interactions in mammalian digestive systems are incredibly complex. A myriad of factors influence the digestive rates and absorption of nutrients required for health. Interest in the factors that can influence nutrient absorption has grown in recent years because evidence supports the viewpoint that it is changes to normal physiological absorption rates that may initiate certain disease processes. It is known for example that low fibre intakes may increase the risk of developing obesity and the metabolic syndrome significantly, possibly due to increases in postabsorptive glycaemia. Similarly, protein can reduce the glycaemic effects of food because the presence of protein in the stomach can inhibit gastric emptying. In addition, some nutrients may have an influence of fat absorption. In particular calcium may form insoluble soaps with fatty acids and increase excretion from the gut while polyphenols may inhibit pancreatic lipase and prevent the absorption of fatty acids.
One line of reasoning therefore suggests that polyphenols are able to fat absorption rates and this may explain some of their health benefits. Wine is a rich source of polyphenolic substances, many of which that have not been characterised in the scientific literature. These polyphenols and their metabolites may decrease the absorption rates of fat in humans as reported in a paper published in the International Journal of Obesity in 20041. Eight subjects with dyslipidaemia consumed red wine with and without alcohol with a mixed meal and their plasma lipids were then measured. Both alcoholic and non-alcoholic red wine decreased the postprandial concentrations of chylomicrons and chylomicrons remnants as measured by a fall in apoB48 levels, suggesting that some component of red wine other than alcohol is able to decrease the absorption of fat.
The mechanism by which polyphenols inhibit fat absorption is not fully understood. However, evidence from human studies investigating the effects of oolong tea on fat excretion2 have shown that 750 mL tea can increase the faecal excretion rates of fat in subject fed 38 gram of fat in the form of potato chips. Lipid excretion rate more than doubled in the tea group, compared to the control group. Cholesterol excretion also increased with tea consumption, but this effect was not as significant when compared to the fatty acids excretion. Therefore like red wine, tea is a rich source of polyphenolic substances that may have an influence on digestion and absorption of macronutrients such as fat. Some evidence suggests that this might be through inhibition of pancreatic lipase in a similar manner to the pharmaceutical drug Orlistat. However, whereas Orlistat is known to cause loose stools, polyphenols do not have this effect.
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