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A User's Guide to Flavonoids

Neil Wagner
 
Flavonoids are a class of antioxidant compound found in many different foods and beverages. Various health benefits have been ascribed to flavonoids for decades. However, it has been difficult for experts to confidently link a particular effect to a particular flavonoid or food. A team at the University of East Anglia in the UK has reviewed over 100 studies on flavonoids and concluded that the flavonoids present in chocolate, soy protein and green tea do confer certain specific cardiovascular health benefits.

An all-chocolate diet appeals to the inner child in most of us, but it's not likely to be healthful.

Nutritional scientists and biochemists have known for decades that antioxidant compounds, at least in theory, are potential lifesavers. They soak up chemicals known as free radicals and may even help prevent their formation. Free radicals are highly energetic molecules that are formed as a byproduct of cellular metabolism. They are extremely destructive to cells and tissues, and have even been suggested as the prime culprit in the aging process.

Flavonoids are a group of antioxidant compounds found in many edible plants. The exact number of known flavonoids is uncertain, but is in the hundreds. Some foods particularly rich in flavonoids are onions, curly kale, leeks, broccoli, blueberries, red wine, green tea and citrus fruits. They are also present in cereals, legumes and other fruits and vegetables.

There have been many studies suggesting a correlation between flavinoids and health over the years concerning the benefits of particular flavonoids and flavonoid containing foods. Unfortunately, there are an astonishing number of compounds and metabolites in the human body and they all interact with each other, so to show that an effect is caused by one particular compound is very challenging indeed.

The team led by Dr. Lee Hooper at the University of East Anglia in Norwich, UK sifted through 133 previous studies done on flavonoids, searching for some unambiguous conclusions. Their research was published in the July issue of The American Journal of Clinical Nutrition. Among their findings:
  1. Eating chocolate or cocoa improved venous blood flow. It also reduced systolic blood pressure by 6 points and diastolic blood pressure by 3.3 points. It did not have an effect on LDL (bad) cholesterol.
  2. Soy protein reduced diastolic blood pressure by about 2 points and lowered LDL-cholesterol. But this was found only for isolated soy protein, not soy products, so it's unclear just how useful this discovery is.
  3. Green tea drinking lowered LDL-cholesterol. Since oolong and black tea have much of their flavonoids destroyed during processing, they are not expected to confer the same benefits. In fact, black tea drinking was found to increase blood pressure (5.6 points systolic, 2.5 points diastolic).
An all-chocolate diet appeals to the inner child in most of us, but it's not likely to be healthful. So what's the lesson here? Dr. Hooper suggests eating a mix of the flavonoid-rich foods you like best. "For me, this would include lots of fruit, small amounts of a good dark chocolate (at least 70 % cocoa), plus the basics like onions and green tea and an occasional glass of red wine."

Since many fruits and vegetables contain high levels of flavonoids, you could also take the approach of adding more fruits and vegetables to a balanced and varied diet. While this sounds much less cutting edge, if you eat a varied enough diet, the good stuff is bound to be in there somewhere. In any case, now you can feel a little less guilt over that next chocolate bar. After all, it's rich in flavonoids.
July 22, 2008



 
 
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