This study, which to the best of our knowledge is the first of its kind, aimed to determine the acute and long-term effects of the consumption of grape and pomegranate juices on endothelium function in adolescents with metabolic syndrome, and to compare the effects of these two kinds of juices.

This randomised controlled clinical trial was conducted in 2008 among 30 adolescents, aged 12–15 years, with metabolic syndrome. Participants were randomly assigned to two groups of equal number; one group was asked to drink 18 millilitre per kilogram per day of natural grape juice and the other group was asked to drink 240 millilitre per day of natural pomegranate juice once daily for 1 month. Juices were homemade without any added sweetener. Basal brachial artery dimension and flow-mediated dilation as an index of endothelial function and endothelial-dependent dilation after receiving nitoglycerin spray were evaluated by high-resolution B mode ultrasonography before juice consumption, 4 hours and 30 days after regular daily consumption.

Flow-mediated dilation at 90 seconds and after nitoglycerin significantly improved at 4 hours and at 1 month after drinking both kinds of juices, without significant difference between the two groups. The change at 1 month versus 4 hours was significant only in the grape juice group.

Daily consumption of diets rich in antioxidants might improve endothelial function in adolescents with metabolic syndrome. These effects began as soon as 4 hours after juice consumption. Such beneficial effects should be considered in dietary recommendations for the paediatric age group, notably in obese individuals.