Favouring Flavonoids?

Flavonoids have long elicited media and medical interest for their potential health benefits as antioxidants, but in early 2007, the Linus Pauling Institute (LPI) published a review on flavonoids that horrified every dark-chocolate lover in North America.

To reference the LPI review see lpi.oregonstate.edu/infocenter/phytochemicals/flavonoids/index.html. An anthology of flavonoid research, endorsed by the LPI, is Flavonoids in Health and Disease, 2nd ed. (Marcel Dekker, Inc., 2003). A large textbook, it may be found in the reference section in your local public or academic library.

What once seemed to be the answer to our antioxidant prayers turns out to be a bit more complicated...and a lot less conclusive.

But Chocolate Just Got Healthy!

Investigators reported in the American Journal of Clinical Nutrition in 2005 that the “antioxidant effects of flavonoids are not supported by strong consistent evidence in vivo” (ajcn.org/cgi/reprint/81/1/268S). Translation: the antioxidant effects of flavonoids may not have much effect inside the body.

Researchers now understand that the antioxidant capacity of flavonoids is decreased when broken down by digestion; the body perceives them as foreign compounds and excretes them rapidly.

A Body is not a Test Tube

It appears that less than 5 percent of flavonoids are absorbed into the bloodstream. Before you give up your dark chocolate, blueberries, and green tea, however, wait for the good news. There is still a marked increase in antioxidants in the blood after we eat flavonoid-rich foods; it just may not be caused by the flavonoids themselves. LPI researchers are still looking at how to explain the increase, but suspect that it may be the result of increased uric acid levels that often come with the digestion of some flavonoids.

Keep Your Soy On

Some of the confusion has come from the 2006 position reversal by the American Heart Association in the US after review of animal model research on soy’s effect on cardio-vascular health revealed inconsistencies circ.ahajournals.org/cgi/content/abstract/circulationaha;114/1/82.
However, conservative researchers say that the flavonoids in soy and other foods still have potential as preventive measures against disease. These scientists caution against using animal studies to determine health in people. Clinical trials on genistein, an isoflavone found in soy, are currently being conducted (pubmedcentral.nih.gov/articlerender.fcgi?artid=1480497).

Just a Dab’ll Do Ya

Since flavonoid-rich foods are generally whole, plant-based foods, no one is suggesting cutting them out of the diet or losing all hope for their prophylactic and protective potential. Ongoing research is looking at their effects on certain cancers and heart disease. While not the antioxidant panacea once thought, flavonoids may still be a health boon.

In recent research, flavonoids have been linked with preventing inflammation in the vascular system, staving off plaque deposits in the brain, and slowing the formation of some cancers. See the following articles online at jpp.krakow.pl/journal/archive/1202/pdf/571_1202_article.pdf, acsinfo.acs.org/cen/coverstory/83/8308alzheimer.html, and
pumedcentral.nih.gov/articlerender.fcgi?artid=321331&tools=bot. However, it may be that small amounts of flavonoids are more beneficial than larger doses that may cause the body stress through the energy it takes to metabolize and eliminate them.

How Much–or How Little?

Researchers have found that green tea, which contains the flavonoid epigallocatechin gallate (EGCG), in doses of about 1,500 to 1,600 mg daily, is safe and may reduce memory loss. Clinical trials of green tea in humans to prevent and treat Alzheimer’s disease are also ongoing. Read more about green tea’s potential health benefits at acsinfo.acs.org/cen/coverstory/83/8308alzheimer.html and jstage.jst.go.jp/article/ehpm/7/6/7_283/_article/-char/en.

Flavonoids require daily replenishment through diet; five to nine servings of fruits, vegetables, soy, and a taste of dark chocolate will supply all the flavonoids you need without taxing the eliminative system. For soy in particular, some research indicates a benefit to menopausal women from isoflavones found in soy products. See atvb.ahajournals.org/cgi/content/abstract/17/12/3392.

In the final analysis of flavonoids… we’re nowhere near a final analysis of flavonoids.