All 41 participants in the randomized, double-blind study had diabetes and took medications. Three times daily, participants blended an 18-gram cocoa mix into 250 ml of water (8 oz). The mix contained either 25 mg (control) or 321 mg (intervention) total flavanols.
It's important to note that the high-flavanol cocoa used in the study was not the same as cocoa you can buy in grocery stores. It was a product called CocoaPro, developed in a proprietary process by Mars, Inc., to retain flavanol content. Mars lent funding to this study.
Flavanols In Foods
Flavanols are a class of flavonoids present in a variety of foods. Besides cocoa and chocolate, which are especially good sources, carob, tea, pinto beans (and other beans), wine, grapes, apples, apricots, bananas, blueberries, cranberries, and other berries contain flavanols (flavanols are not the same as flavonols). The USDA maintains a database of flavanols, and other flavonoids, in foods. You can access it at:
USDA Database for the Flavonoid Content of Selected Foods, Release 2.1 (2007)
Below are some specific foods along with their flavanol content.2 (Catechin and epicatechin are both flavanols.) Values are given in milligrams of flavanols per 100 grams of food - that would be about 1/4 pound of grapes, apples, etc.
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Note that none of these foods (per 100 gram serving) contain the amount of flavanols used in one cup of cocoa from the study (321 mg). In fact, they come closer to the amount found in the control. Unless you're consuming Mars' patented CocoaPro - 3 times daily - you likely won't consume enough flavanols regularly to achieve the results seen in this study.
1 Sustained Benefits in Vascular Function Through Flavanol-Containing Cocoa in Medicated Diabetic Patients, Journal of the American College of Cardiology, 2008
2 Cocoa Flavanols And Cardiovascular Health, 2004