Most Americans fall far short of the intakes of fruits and vegetables advised by U.S. health agencies.
Although some evidence suggests that diets higher in fruits and vegetables reduce cancer risks, the jury remains out.
Instead, the USDA's “Five-A- Day” campaign and similar ones rest primarily on evidence linking diets high in fruits and vegetables to lower risk of cardiovascular disease.
The cardiovascular benefits of fruits and vegetables – and their presumed but less certain anti-cancer effects – flow from these foods' “antioxidant” polyphenol compounds … especially flavonoids.
Population (epidemiological) studies consistently associate higher fruit, vegetable, and vitamin C intake with reduced stroke risk.
Now the results of two studies – one clinical and one epidemiological – indicate cardiac benefits from foods rich in two sub-groups of flavonoids:
Flavanones (eriodictyol, hesperetin, naringenin) abound in all citrus fruits
Flavanols (catechins, epicatechins, proanthocyanidins) abound in tea, grapes, kiwi fruit, and raw, non-Dutched cocoa and in dark chocolate containing 60 percent or more raw cocoa solids.
In January of this year, scientists from the UK's University of East Anglia (UEA) reported that an antioxidant-enriched dark chocolate reduced cardiovascular risks among post-menopausal women with diabetes.
And last month, another UEA team reported that an epidemiological study linked diets high in flavanone-rich citrus fruits to a 19 percent drop in women's stroke risk.
Citrus linked to re lower stroke risk among women
The University of East Anglia team collaborated with Harvard's Eric Rimm, Sc.D., on a study in which they analyzed diet and health data collected from 69,622 women who took part in the 14-year-long Nurse's Health Study (Cassidy A et al. 2012).
The UEA-Harvard team looked for relationships between each of the six subclasses of flavonoids most abundant in western diets and risk of ischemic stroke (the most common kind by far, caused by blood clots), hemorrhagic stroke, and all strokes.
No significant associations were found between total flavonoid intake and stroke risk, probably because the physiological effects of the sub-classes differ.
However, the women who reported eating the diets richest in flavanones (mostly from citrus fruits) were 19 percent less likely to suffer an ischemic stroke, compared with those estimated to consume the least flavanones.
As the researchers wrote, “… [this finding] fits with existing data on the protective effect of citrus fruit consumption.” (Cassidy A et al. 2012)
Lead author Aedín Cassidy noted that flavonoids appear to stimulate or enhance several protective mechanisms, “… including improved blood vessel function and an anti-inflammatory effect.”
Dark chocolate deterred heart disease in diabetic women
A separate UEA team conducted a 12-month trial among 93 postmenopausal women with type 2 diabetes, whose ages ranged from 51 to 74 (Curtis PJ et al. 2012).
Postmenopausal women with diabetes were chosen for the trial because they are a very high risk group for heart disease, even if they take statin drugs. The study was funded by Diabetes UK.
The risk of death related to heart disease rises sharply after menopause, and having type 2 diabetes increases that risk by a whopping 350 percent (UEA 2012).
Prior studies indicate that dietary flavonoids reduce the risk factors for heart disease in healthy people.
This trial was the first long-term study to examine their effect on a medicated, high-risk group.
Half of the women ate two small bars of flavonoid-enriched chocolate daily, and half were given placebo chocolate bars.
Importantly, women who were taking diabetes or heart drugs continued taking these medications during the trial and 10 years of follow-up.
The chocolate bars used in the trial were enriched with more of the epicatechin-type flavanols naturally abundant in cocoa, and with certain of the isoflavone-class flavonoids found in soy beans.
The women in the test chocolate group were 3.4 percent less likely to suffer a heart attack in the next decade.
This may sound like a small impact, but it would be considered a very substantial preventive effect for any “dietary intervention”.
Better yet, their insulin resistance and cholesterol levels were significantly lower than the control (placebo chocolate) group.
As Dr. Cassidy said, “These results are significant from a public health perspective because they provide further concrete evidence that diet has a beneficial clinical effect over and above conventional drug treatment.” (UEA 2012)
Chocolate and flavanols: Study authors sowed semantic confusion
Although the authors said that the test bars had more flavonoids than are found in “commercially available” bars, that is not accurate.
The “test” chocolate bars given to half of the women contained 850mg of flavanols (including 90mg epicatechin) and 100mg of isoflavones (from soy).
It's not clear why the researchers chose to add isoflavones, and such a modest amount. Soy isoflavones do appear to benefit to arterial health, but cocoa flavanols have considerably more and better evidence in this regard. (Gil-Izquierdo A et al. 2011)
In other words, just one-quarter bar of our chocolate provides more than eight times as much epicatechin as each of the test bars used in this trial.
How can we explain this discrepancy between the authors' characterization of the test bars, and reality?
When the UEA team said “commercially available” chocolate, they probably meant milk chocolate (30% cocoa solids), which contains few flavanols.
Even bars labeled “dark chocolate” may contain only 55% cocoa solids, and would have many fewer flavanols than an 80% cocoa bar like ours.
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