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Fruits Regain Antioxidant Crown After Brief Loss to Whole Grains
9/10/2009
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New findings put fruits back on top of the scale thanks to “hidden” polyphenols, and show that many of these fiber-bound, previously unmeasured antioxidants in fruits are absorbed

by Craig Weatherby


What a difference a month (or less) makes!


In a recent issue of Vital Choices, we reported that previously unknown levels of polyphenol-type antioxidants had been found in whole grains and whole grain products.


A polyphenol primer

While polyphenols are best known as antioxidants, they appear to enhance health in many other ways.


These include polyphenols’ ability to neutralize damaging free radicals, their anti-inflammatory influences on genetic switches in our cells, and their likely DNA-protective properties.


Polyphenols occur most abundantly in raw cocoa (the richest known source), spices, herbs, tea, colorful fruits and vegetables (e.g., berries and spinach), and in wild salmon, nuts, coffee, olives, and extra-virgin grade olive oil.


Polyphenols also serve as pigments that give fruits (and wild salmon) their bright hues.


The polyphenol family encompasses vitamin E, carotenes (including the astaxanthin that makes wild salmon red), the anthocyanins in fruits and veggies with red-blue-purple colors, and the potent tyrosol compounds unique to olives.

This unexpected finding seemed to crown whole grains as the kings of antioxidant content, above colorful fruits and vegetables (See “Whole Grain Foods Found High in Antioxidants”).


That apparent upset in the relative antioxidant-power rankings of whole grains vs. fruits and vegetables came about because many of the polyphenols in whole grains are bound up in fiber, and had not been measured previously.


We suspected that the victory of grains over fruits would prove fleeting, and it has.

Now, a joint Anglo-Spanish research team has reported finding that apples, peaches and nectarines contain up to five times more polyphenols than previously thought... findings that likely extend to other common fruits (Arranz S et al. 2009).


And another study, also published this summer, shows that very substantial amounts of these “hidden,” fiber-bound polyphenols get absorbed into the blood of fruit consumers (Pérez-Jiménez J et al. 2009).


Anglo-Spanish study boosts the antioxidant ranking of colorful fruits

In what seems like a counter-punch from colorful fruits, an international team has published the results of a study similar to the whole grain experiment (Arranz S et al. 2009).


Like the whole grain study, this one was designed to quantify any previously unmeasured, so-called “non-extractable” polyphenols imbedded in the fibrous parts of three common fruits.


(By “non-extractable” the researchers mean polyphenols that weren’t detected using the usual methods of isolating these compounds from foods… it would be more accurate to call them “previously non-extractable” polyphenols.)


Polyphenols found in fruit-fiber cells have largely been ignored because they cannot be broken down and measured in the lab as easily as polyphenols that have been easier to extract from fruit.


And many have assumedwrongly, as we shall seethat the body cannot extract and absorb most fiber-bound polyphenols during digestion.


Study co-author Sara Arranz of the Spanish Council for Scientific Research explained their method in a news release: “These [non-extractable] polyphenols need to be treated with acid to extract them from the cell walls of fruit in the lab” (IRF 2009).


She and her colleagues found that the amount of previously “non-extractable” polyphenols in apples, peaches and nectarines exceeded the amount of easily extractable polyphenols.


In other words, researchers have been seriously undercounting the levels of antioxidants occurring in fruits.


This finding puts fruits back on top above whole grains, whose moment in the antioxidant-champ sun was all too brief.


Arranz went on to make a key point: “If these [previously] non-extractable polyphenols are not considered, the levels of beneficial polyphenols, such as proanthocyanidins, ellagic acid and catechin are substantially underestimated” (IRF 2009).


And if these previously un-measured polyphenols are absorbed by the body, it would mean that, as Arranz said, “…they actually represent a major part of the effective [antioxidant] compounds in the human diet” (IRF 2009).


Earlier clinical study shows fiber-bound antioxidants get absorbed

The new findings from Britain suggest that fiber-bound polyphenols may constitute most of the polyphenols in plant foods.


If that’s true, we need to know whether the body can actually extract fiber-bound polyphenols from fruits and other plant foods.


Coincidentally, just two months before the new finding that fruits have loads of fiber-bound polyphenols, a team from Spain’s national Institute of Food Science, Technology and Nutrition undertook a clinical study designed to discover whether the antioxidants in plant foods actually get absorbed into the bloodstream (Pérez-Jiménez J et al. 2009).


The answer to this question was a resounding “yes”… people do absorb significant amounts of the fiber-bound polyphenols in plant foods, with significant positive impacts on the “antioxidant capacity” of their blood.


This matters because hundreds of studies link higher antioxidant capacity in the blood to a variety of beneficial effects on inflammation, artery health, and much more.


As the Spanish team noted, most studies on the “bio-availability” (i.e., the absorbability) of polyphenol-type antioxidants have involved low-fiber plant foods and beverages, whose polyphenols are easily extracted and absorbed during digestion.


In those studies, blood levels of polyphenols typically reach a peak one to two hours after a meal, showing that polyphenols are indeed absorbed.


But what about fibrous plant foods, more of whose polyphenols are bound up in harder-to-digest fibers?


To find out, they divided 34 volunteers into two groups. The test group consumed 15 grams (about one-half ounce) of a dietary fiber rich in polyphenols, while the control group did not consume the antioxidant-rich fiber.


They drew blood from both groups, and found that, eight hours after eating the test or control food, the antioxidant capacity of blood of people in the test group was significantly higher compared with the blood from the control group.


As the Spanish research team wrote, “This shows that phenolic antioxidants [polyphenols] associated with dietary fiber are at least partially bio-available in humans, although dietary fiber appears to delay their absorption” (Pérez-Jiménez J et al. 2009).


Following the short-term, eight-hour trial, all 34 subjects in the Spanish study continued to eat one-half ounce of polyphenol-rich fiber daily for four months.


In accordance with the findings of most prior studies, the antioxidant capacity of their blood did not remain higher than before the study.


However, if you’ll excuse the pun, this does not mean that eating polyphenol-rich foods frequently is a fruitless endeavor, as we'll explain.


Despite long-term finding, daily polyphenols are clearly beneficial

The Spanish researchers postulated that the body adjusts to higher intake of polyphenols or other plant-borne antioxidants by reducing production of some components of its internal “antioxidant network” (This network consists largely of vitamins C and E, alpha lipoic acid, melatonin, and antioxidant enzymes).


While we can’t be certain, it may be that by easing the body’s need to produce its own antioxidants, dietary antioxidants allow it to spend that energy on other needs.


And, more certainly and importantly, dozens of population studies link higher intake of polyphenol-rich foods to lower rates of major diseases, including certain cancers, heart disease, and Alzheimer’s.


This may be because polyphenols and other dietary antioxidants offer benefits beyond their ability to help control the cell-damaging, pro-inflammatory, pro-oxidant compounds known as free radicals, which drive premature aging and promote or exacerbate major chronic diseases.


In addition to acting as antioxidants, polyphenols also influence the genetic switches in our cellscalled nuclear transcription factorswhich can raise or lower inflammation levels and affect many other metabolic functions that impact overall health.


A next logical step for scientists is to measure the relative absorbability and antioxidant impact of non-extractable polyphenols found in various fruits and other plant foods, so that we can identify the ones with the highest levels of absorbable polyphenols.


Together, these two new studies affirm fruits as the top antioxidant sources, and seem to support the notion that eating ample amounts of antioxidant-rich plant foods is an easy, tasty way to promote general health and well-being.



Sources

  • Arranz S, Saura-Calixto F, Shaha F, Kroon PA. High contents of nonextractable polyphenols in fruits suggest that polyphenol contents of plant foods have been underestimated. Journal of Agricultural and Food Chemistry, August 2009, Volume 57, Issue 16, Pages 7298-7303.
  • Goñi I, Serrano J, Saura-Calixto F. Bioaccessibility of beta-carotene, lutein, and lycopene from fruits and vegetables. J Agric Food Chem. 2006 Jul 26;54(15):5382-7.
  • Goñi I, Serrano J, Saura-Calixto F. Bioaccessibility of beta-carotene, lutein, and lycopene from fruits and vegetables. J Agric Food Chem. 2006 Jul 26;54(15):5382-7.
  • Institute of Food Research (IRF). Fruit is even better for you than previously thought. August 9, 2009. Accessed September 8, 2009 at http://www.ifr.ac.uk/info/news-and events/NewsReleases/090826polyphenols.html. Fulgencio Saura-Calixto, José Serrano and Isabel Goñi. Intake and bio-accessibility of total polyphenols in a whole diet. Food Chemistry, Volume 101, Issue 2, 2007, Pages 492-501. Accessed at http://www.sciencedirect.com/
  • Pérez-Jiménez J, Serrano J, Tabernero M, Arranz S, Díaz-Rubio ME, García-Diz L, Goñi I, Saura-Calixto F. Bioavailability of phenolic antioxidants associated with dietary fiber: plasma antioxidant capacity after acute and long-term intake in humans. Plant Foods Hum Nutr. 2009 Jun;64(2):102-7.

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