Health effects of natural phenols and polyphenols
Because of the large structural diversity and extensive metabolism of dietary polyphenols, their fate in vivo and possible health effects remain undetermined as of the early 21st century. Although polyphenols are speculated to be part of the health-promoting effects of consuming fruits and vegetables, no evidence exists to date that dietary polyphenols actually provide health benefits.
Polyphenols have poor bioavailability, indicating that most of what are consumed are extensively metabolized and excreted. Gallic acid and isoflavones may show absorption of about 5%, with amounts of catechins (flavan-3-ols), flavanones, and quercetin glucosides even less. The least well-absorbed phenols are the proanthocyanidins, galloylated tea catechins, and anthocyanins.
A review published in 2013 found insufficient consensus for the hypothesis that the specific intake of food and drink containing flavonoids may play a meaningful role in reducing the risk of cardiovascular diseases. The reviewers stated that research to date had been of poor quality and that large and rigorous clinical trials are needed to define health benefits and to reveal adverse events from excessive polyphenol intake. Currently, lack of knowledge about safety suggests that polyphenol levels should not exceed the intake of a normal diet.
Preliminary research on the association of consuming polyphenol foods, such as olive oil, soy, and pomegranate products, with lower risk of cardiovascular diseases has been low in quality, with little evidence of any possible benefit.
As interpreted by the Linus Pauling Institute and the European Food Safety Authority (EFSA), dietary flavonoids have little or no direct antioxidant food value following digestion. Unlike controlled test tube conditions where antioxidant effects may result when high concentrations of flavonoids are used, the fate of ingested flavonoids in vivo shows they are poorly conserved (less than 5%), with most of what is absorbed existing as chemically-modified metabolites destined for rapid excretion.
- "Flavonoids". Linus Pauling Institute, Micronutrient Information Center, Oregon State University. 2015. Retrieved 8 June 2015.
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)2, 3 European Food Safety Authority (EFSA), Parma, Italy (2010). "Scientific Opinion on the substantiation of health claims related to various food(s)/food constituent(s) and protection of cells from premature aging, antioxidant activity, antioxidant content and antioxidant properties, and protection of DNA, proteins and lipids from oxidative damage pursuant to Article 13(1) of Regulation (EC) No 1924/20061". EFSA Journal. 8 (2): 1489. doi:10.2903/j.efsa.2010.1489.
- Del Rio D, Rodriguez-Mateos A, Spencer JP, Tognolini M, Borges G, Crozier A (May 2013). "Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases". Antioxidants & Redox Signaling. 18 (14): 1818–92. doi:10.1089/ars.2012.4581. PMC 3619154. PMID 22794138.
- Manach C, Williamson G, Morand C, Scalbert A, Rémésy C (January 2005). "Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies". The American Journal of Clinical Nutrition. 81 (1 Suppl): 230S–242S. doi:10.1093/ajcn/81.1.230S. PMID 15640486.
- Habauzit V, Morand C (March 2012). "Evidence for a protective effect of polyphenols-containing foods on cardiovascular health: an update for clinicians". Therapeutic Advances in Chronic Disease. 3 (2): 87–106. doi:10.1177/2040622311430006. PMC 3513903. PMID 23251771.
- Marx W, Kelly J, Marshall S, Nakos S, Campbell K, Itsiopoulos C (December 2017). "The Effect of Polyphenol-Rich Interventions on Cardiovascular Risk Factors in Haemodialysis: A Systematic Review and Meta-Analysis". Nutrients. 9 (12). doi:10.3390/nu9121345. PMC 5748795. PMID 29232891.
- George ES, Marshall S, Mayr HL, Trakman GL, Tatucu-Babet OA, Lassemillante AM, Bramley A, Reddy AJ, Forsyth A, Tierney AC, Thomas CJ, Itsiopoulos C, Marx W (April 2018). "The effect of high-polyphenol extra virgin olive oil on cardiovascular risk factors: a systematic review and meta-analysis". Critical Reviews in Food Science and Nutrition: 1–138. doi:10.1080/10408398.2018.1470491. PMID 29708409.
- Williams RJ, Spencer JP, Rice-Evans C (April 2004). "Flavonoids: antioxidants or signalling molecules?". Free Radical Biology & Medicine. 36 (7): 838–49. doi:10.1016/j.freeradbiomed.2004.01.001. PMID 15019969.