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Key Points
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Clinical trial confirms that the antioxidants in berries end up in our blood.
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Findings support earlier clinical, cell, and animal studies showing that berries yield heart and brain benefits.
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Food-borne antioxidants deliver their benefits as much or more via their influence over our genes, versus their direct antioxidant effects.
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Articles about the antioxidants in fruits, tea, and chocolate usually focus on the amounts found in each food or beverage.
Or, they’ll focus on the antioxidant power a food displays in the test tube, usually expressed as a number on the “oxygen radical absorbance capacity” or ORAC scale.
However, a laboratory measure of a food’s antioxidant content or capacity only go so far toward predicting its health-enhancing potential.
In part, this is because a food’s rank on the ORAC or similar scales can’t tell us whether, or to what extent any of its antioxidants are absorbed by the body … the property known as “bioavailability”.
And it’s becoming increasingly clear that the apparent benefits of antioxidants in foods relate as much or more to their influence on various genes – an emerging science called nutrigenomics – as to their direct antioxidant effects.
For example, many polyphenols in plant foods reduce activation of Nf-kappaB: a “DNA transcription factor” protein complex, activation of which is linked to inflammatory diseases including cancer, atherosclerosis, diabetes, allergy, asthma, arthritis, Crohn’s disease, and Alzheimer's disease.
Absorption is critical to antioxidants' potential benefits
A food-borne antioxidant that’s shown health-enhancing promise in test tube or animal studies will be useless to people unless a significant proportion is absorbed into the blood and/or other body tissues.
We need much more evidence on the bioavailability of specific antioxidants in fruits, vegetables, nuts, seeds, grains, beans, tea, cocoa, and more.
Antioxidant tests like ORAC cannot distinguish among the many antioxidant compounds in a food, in terms of their bioavailability.
Nor do test tube measures like ORAC say anything about the absorption or health effects of the “metabolites” created when the body digests food-borne antioxidants.
(Considerable evidence indicates that some of the metabolites created during the body’s processing of food-borne antioxidants exert substantial beneficial effects.)
So it comes as welcome news that participants who ate berries in a controlled clinical trial enjoyed big boosts in their blood levels of several berry-borne antioxidants.
Finnish trial confirms absorption of berry-borne antioxidants
Researchers from the Finnish National Institute for Health and Welfare recruited 72 middle-aged people to participate in a placebo-controlled clinical trial (Koli R et al. 2010).
The volunteers were randomly assigned to receive either 160 grams (5.7 oz) of berries a day as a puree or juice, or placebo food or drink, for eight weeks. (The placebos included sugar water, sweet semolina or rice porridge, and jelly sweets.)
The daily berry snack provided about 837 mg of various types of polyphenols, which nearly doubled the estimated average intake among Finnish adults (about 860 mg per day).
Compared with the control group, the berry-fed group showed substantial increases in their blood levels of key polyphenol antioxidants.
(For example, levels of quercetin were up to 84 percent higher, p-coumaric acid levels were 40 percent higher, caffeic acid levels were 100 percent higher, vanillic acid levels were 31 percent higher, and propionic acid levels were up to 31 percent higher.)
These blood-level increases were accompanied by significant increases in the levels of various polyphenols in the berry groups’ urine, indicating that they had been absorbed before being excreted.
The study authors were clear about the meaning of their trial: “In conclusion, polyphenols are bioavailable from berries ...” (Koli R et al. 2010)
They also made a key point about the difference between a food’s antioxidant content and the impact on those compounds in the body:
“… due to … differences in the degree of uptake of different polyphenols, the polyphenol profile in plasma [blood] and urine differ greatly from the polyphenol profile in berries.” (Koli R et al. 2010)
As they wrote, “The potential health effects of these compounds, particularly the metabolites, should be explored further.” (Koli R et al. 2010)
They can say that again, given the pittance spent researching non-patentable food factors such as berry antioxidants, versus the billions lavished on patentable, hence highly profitable synthetic drugs … many of which produce adverse effects and ultimately prove only marginally effective.
Sources
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Erlund I, Freese R, Marniemi J, Hakala P, Alfthan G. Bioavailability of quercetin from berries and the diet. Nutr Cancer. 2006;54(1):13-7. Review.
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Erlund I, Koli R, Alfthan G, Marniemi J, Puukka P, Mustonen P, Mattila P, Jula A. Favorable effects of berry consumption on platelet function, blood pressure, and HDL cholesterol. Am J Clin Nutr. 2008 Feb;87(2):323-31.
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Erlund I, Marniemi J, Hakala P, Alfthan G, Meririnne E, Aro A. Consumption of black currants, lingonberries and bilberries increases serum quercetin concentrations. Eur J Clin Nutr. 2003 Jan;57(1):37-42.
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Koli R, Erlund I, Jula A, Marniemi J, Mattila P, Alfthan G. Bioavailability of Various Polyphenols from a Diet Containing Moderate Amounts of Berries. J Agric Food Chem. 2010 Jan 14. [Epub ahead of print]
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Marniemi J, Hakala P, Mäki J, Ahotupa M. Partial resistance of low density lipoprotein to oxidation in vivo after increased intake of berries. Nutr Metab Cardiovasc Dis. 2000 Dec;10(6):331-7.
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Törrönen R, Sarkkinen E, Tapola N, Hautaniemi E, Kilpi K, Niskanen L. Berries modify the postprandial plasma glucose response to sucrose in healthy subjects. Br J Nutr. 2009 Nov 24:1-4. [Epub ahead of print]
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