Flavan-3-ols are a subgroup of flavonoids. Flavan-3-ols are sometimes called catechins as they include the chemicals catechin and epicatechin and their gallate conjugates. Flavan-3-ols are found in high concentrations in tea as monomeric units, and their presence may explain the health benefits of regular tea consumption. Other foods that contain high concentrations of flavan-3-ols include cocoa, apples and cinnamon. In cocoa, flavan-3-ols are present mainly as dimers, trimers and polymers. Epidemiological studies suggest that flavan-3-ol intake is inversely associated with cardiovascular disease, and it has been hypothesised that this may relate to the antioxidant effects of flavonoids. Further, insulin resistance is increasingly being implicated in the aetiology of cardiovascular disease. The beneficial effects of flavan-3-ols against cardiovascular disease may result from the insulin sensitising effects they possess. For example, cinnamon has been researched and shown to have insulin mimetic effects. Green tea and cocoa have also been shown to have particular insulin sensitising effects.
Therefore the health benefits of flavan-3-ols may derive from their antioxidant properties, through insulin sensitising effects. A number of reviews have investigated the insulin sensitising effects of flavan-3-ols. For example, in one study1, researchers analysed clinical trials of studies investigating flavan-3-ol ingestion using a meta-analysis. The results of the study showed a significant effect at reducing insulin resistance for chocolate and cocoa consumption, and this insulin sensitising effect was accompanied by a reduction in fasting plasma insulin levels. Improvements in flow mediated dilation were also evident following chronic ingestion of chocolate and cocoa, and this was reflected by a reduction in diastolic blood pressure and mean arterial blood pressure. Chocolate was beneficial at improving flow mediated dilation at any dose. However, intakes of over 50 mg of epicatechin, one of the flavan-3-ols in chocolate, produced larger improvements in systolic and diastolic blood pressure.
Therefore, foods containing flavan-3-ols may have particular insulin sensitising effects, and these effects may produce beneficial effects against cardiovascular disease. Interestingly in this meta-analysis, small improvements in blood lipid profile were also reported with chocolate consumption. This included small reductions in low density lipoprotein (LDL) and small increases in high density lipoprotein (HDL). These improvements in blood lipid profiles may have resulted from the lowering of fasting insulin levels, as raised levels of insulin may be a cause of changes to lipid metabolism and transport which includes changes to lipoprotein ratios. Cinnamon, green tea, black tea and chocolate consumption is inversely associated with body weight, and although this may reflect the higher quality diets consumed by individuals that consume these foods, it may also suggest that the insulin sensitising effects of flavan-3-ols causes particular weight loss effects. Certainly evidence is mounting that green tea is a weight loss food, possibly because of its high flavan-3-ol content.
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