Not all flavonoids are created equal according to a new analysis

July 24, 2008

      An increased consumption of flavonoid-rich cocoa and soy isolated protein may decrease blood pressure and improve heart health, and drinking Green Tea improves cholesterol but other flavonoids in food sources are not as effective, according to a new meta-analysis. There is a wealth of studies reporting beneficial effects for the compounds from chocolate, soy and tea reports lead author Lee Hooper from the University of East Anglia in the United Kingdom.
     Hooper and co-workers included 133 trials in their meta-analysis. A vast body of epidemiological studies has linked increased dietary intake of antioxidants from fruits, vegetables wine, chocolate, coffee, tea, and other foods to reduced risks of a range of diseases including cancer, cardiovascular disease and diabetes.
     Flavonoids can be split into a number of sub-classes, including anthocyanins found in berries, flavonols from a variety of fruit and vegetables, flavones from parsley and thyme, for example, flavanones from citrus, isoflavones from soy, mono- and poly-meric flavonols like the catechins in tea, and proanthocyanidins from berries, wine and chocolate. The non-flavonoids include phenolic acids, lignans, and Stilbenes such as Resveratrol. It is important to note that standardized extracts were not examined in this study, in other words the amount of OPCs in a Grape Seed capsule could not be matched by eating grapes so benefits of isolated supplements are not part of this analysis.

     The researchers used the data from the 133 studies and found wide variations in effects depending on the nature of the flavonoid and the food source. Flavonoids from cocoa rich chocolate were associated with a four per cent increase in blood flow, and a reduction in systolic and diastolic blood pressure of 5.88 and 3.30 mmHg, respectively. Significant blood pressure reductions were also observed for soy protein isolate, but not other soy products or components, said the researchers. Moreover, LDL cholesterol reductions were also observed.
     Pooling the results of trials looking at green tea consumption, Hooper and co-workers found that the flavonoids reduced LDL cholesterol levels.
systolic and diastolic blood pressure of 5.69 and 2.56 mmHg, respectively.
In an accompanying editorial, Johanna Geleijnse and Peter Hollman from Wageningen University in the Netherlands noted that the contribution of flavonones to a person's antioxidant capacity was significant.
"More than 6000 different flavonoids in plants have been described, and their total intake could amount to 1 g/d, whereas combined intakes of beta-carotene, vitamin C, and vitamin E from food most often are less than 100 mg/d," they said. The study is published in the July 1st, 2008 issue of the American Journal of Clinical Nutrition