The flavan-3-ols are a subgroup of flavonoids. The flavan-3-ols are found as monomeric units in green tea mainly as catechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate. In black tea the main flavan-3-ols are theaflavins and thearubigins. The monomeric flavan-3-ols are also found as dimers, trimers and polymers in some foods including cocoa, and when in this form are referred to as proanthocyanidins. Chocolate is therefore a good source of flavan-3-ols, as long as the cocoa content of the product is high. As flavan-3-ols have been extensively studied and found to possess particular health effects, theses effects are conferred on those who consume chocolate. Like most flavonoids, the flavan-3-ols are bioavailable in animals and humans, and once absorbed they act as chain breaking antioxidants. In this way they may support the endogenous antioxidants of the cells to allow protection from free radical damage. In addition, flavan-3-ols may be involved in gene regulation.
Green tea has been shown to possess particular weight loss effects, and these effects have been suggested to be due to the high content of flavan-3-ols. Studies investigating flavan-3-ols show they may have properties that could cause weight loss, particularly with regard to the insulin system. Flavan-3-ols appear able to improve insulin sensitivity through an unknown mechanism, possibly through the termination of free radical chain reactions and a reduction in the levels of oxidative stress experienced by cells. As oxidative stress may be implicated in the aetiology of insulin resistance, this mechanism explains the insulin sensitising effects of green tea, and provides a scientifically rational explanation for the weight loss effects of green tea. That chocolate also possesses insulin sensitising effects, may suggest that it too could potentially be a weight loss food. Studies have investigated the effects of chocolate on insulin sensitivity in humans and shown that like tea it is able to reverse insulin resistance.
For example, in one study1, researchers investigated the effects of flavan-3-ol rich chocolate on endothelial function and insulin sensitivity in hypertensive patients. The fact that these patients had elevated fasting blood glucose levels suggest that they had significant metabolic dysfunction possibly including metabolic syndrome. The subjects consumed either 100 grams per day of flavan-3-ol rich dark chocolate or flavan-3-ol free white chocolate for 15 days. The results of the study showed that the flavan-3-ol rich dark chocolate was able to improve insulin sensitivity, improve β-cell function and also cause a reduction in both diastolic and systolic blood pressure, but the white chocolate was not effective in this regard. The improved insulin sensitivity and β-cell function were correlated with increases in the flow mediated dilation and inversely correlated with blood pressure. Dark chocolate therefore provides significant health, including insulin sensitising effects, and could therefore be considered a weight loss food.
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