What’s So Powerful About Polyphenols?
By: Stephen T. Sinatra, M.D., F.A.C.C., F.A.C.N., C.N.S., C.B.T.
It is no secret that I’m a huge fan of olive oil. I love everything about it—the way it tastes, the way it smells, its versatility of it, and – most importantly – the fact that olive oil also happens to be incredibly good for you.
Olive oil’s many health benefits come courtesy of a unique combination of monounsaturated fat and antioxidants called polyphenols. Polyphenols are phytochemicals – natural compounds plants make to protect themselves from various stressors, including pathogens, environmental assaults, ultraviolet radiation, and even bugs and other pests. When we eat plants that are high in polyphenols, those same protective compounds also help safeguard our health.
Foods High In Polyphenols
Polyphenols are also what give plant foods their distinctive aromas and flavors. You can find polyphenols in many different types of fruits and vegetables—including grapes, olives, spinach, red onion, and berries – as well as in flaxseed and nuts. (Keep in mind, products with darker skin tend to have higher polyphenol content. So while all grapes contain polyphenols, red grapes are a richer source than green.) Dried herbs and spices like cloves, peppermint, and rosemary are especially high in polyphenols.
Polyphenols are also abundant in beverages made from plants, like black and green tea, coffee, and red wine (thanks to the dark red grapes used to make it). They’re even in cocoa, making a small square or two of low-sugar dark chocolate a relatively healthy choice when you want to indulge your sweet tooth!
There are thousands of different types of polyphenols, which can be further broken down into four specific classes: flavonoids, stilbenes, phenolic acids, and lignans. Many studies show that polyphenols as a whole can help reduce the risk of Alzheimer’s and other neurodegenerative diseases, type 2 diabetes, cancer, osteoporosis, and other chronic and debilitating conditions. Early research indicates that certain polyphenols can even help extend lifespan and improve healthspan (how vibrant, healthy, and disease-free you are in your later years).
But as a cardiologist, I’m most interested in polyphenols for their many heart benefits. While you can garner cardiovascular protection from many different polyphenols (such as resveratrol from red grapes and wine), there’s a reason I consider olive oil a “superfood.” Its protective powers come from its robust levels of phenolic compounds. In fact, olive oil has at least 30 phenolic compounds, including oleuropein and hydroxytyrosol.
Benefits of Phenolic Compounds in Olive Oil
As you know, olive oil is one of the foundations of the Mediterranean diet, as well as my own variation of this diet called the PAMM diet. And based on all the research, I’ve come to view olive oil, really, as the “secret sauce” of the Mediterranean diet. One of the most convincing studies for me was the 2013 PREDIMED study—the first large clinical trial to show that the Mediterranean diet can reduce the incidence of heart attacks and strokes, and thus provide primary cardiovascular protection (meaning it can stop initial cardiovascular events).
The study had nearly 7,500 participants. While none had cardiovascular disease, they did have either type 2 diabetes or major risk factors for disease, such as high blood pressure, elevated LDL cholesterol, low HDL (beneficial) cholesterol, obesity, or a family history of heart disease.
The participants were randomly assigned to one of three diets: a Mediterranean diet supplemented with four tablespoons per day of extra-virgin olive oil; a Mediterranean diet supplemented with nuts; or a control diet, which was a standard Western-style low-fat diet.
After nearly five years, researchers determined that those on the olive oil-enhanced diet had a rate of cardiovascular events approximately 30 percent less than those on the low-fat diet. Just as exciting: Those consuming the extra four tablespoons of olive oil every day were adding about 50 grams of extra fat to their diets. Yet nobody gained any weight as a result! (All of this flies in the face of the American Heart Association and other cardiology groups, which continue to recommend low-fat diets for heart disease prevention and weight loss.)
Earlier olive oil studies yielded similarly impressive results. In one, published in 2011, researchers investigated the link between fruit, vegetable, or olive oil consumption and the incidence of heart disease in nearly 30,000 women. After eight years, they found that the women who ate the most vegetables and olive oil had the strongest defense against heart disease.
In 2010, a Spanish study came out that got me really excited about olive oil – it showed that eating 40 ml (almost 3 Tbsp) of olive oil at breakfast, actually had a positive impact on the participants’ genes. That’s right – it impacted how their bodies expressed their God-given genes. Nearly a hundred genes related to diabetes, obesity, and blood lipids were affected in a healthy way by the phenolic compounds in olive oil, and some of the genes – ones that are intimately involved in the body’s inflammatory process – were actually repressed! This was such promising news for me, given that uncontrolled inflammation is the common denominator between most chronic degenerative diseases like heart disease.
To be fair, a lot of the cardiovascular benefits of olive oil are due to the monounsaturated fat content. A 2011 study looked at blood levels of oleic acid (a primarily monounsaturated fatty acid found in olive oil) and the incidence of stroke. Compared to those who never consumed olive oil (and therefore had low levels of oleic acid), those with higher blood levels had a 73 percent lower incidence of stroke.
But the more olive oil has been tested in recent years, the clearer it has become that the polyphenol/phenolic acid content is just as, if not more, powerful. According to a 2014 study published in the Journal of Translational Medicine:
“Initially, the richness of monounsaturated fatty acids (MUFA), and in particular oleic acid, was considered as the major healthful characteristic of [olive oil]. Later on, after the observation that other aliments rich in MUFA, such as rapeseeds, soybean, and sunflower, were not comparable with [olive oil] as a healthful food, the role of some ‘minor components’ has been taken into consideration…
Particular attention has been focused on the nutraceutical properties of those compounds provided with antioxidant activity…. Oleuropein (OL) and hydroxytyrosol (HT) represent molecules of major interest for their biological and pharmacological properties, and, with no doubt, are among the most investigated antioxidant natural compounds.”
Oleuropein and hydroxytyrosol not only serve as potent antioxidants, but they also exhibit antimicrobial and anti-inflammatory activity, promote healthy blood vessel dilation, and reduce the risk of dangerous blood clotting.
A 2010 study that looked specifically at oleuropein concluded that this phenolic compound prevents lipoprotein oxidation (which dramatically ups the risk of cardiovascular disease), protects against strokes and chemotherapy-induced heart issues, and naturally lowers cholesterol.
Hydroxytyrosol bestows equally remarkable benefits, including the prevention of plaque buildup in the arteries. In an animal study, rabbits given hydroxytyrosol for one month ended up with improved cholesterol profiles, elevated blood antioxidant status, and decreased size of atherosclerotic lesions in their arteries.
Most recently, in a 2017 study with mice, researchers found that extra virgin olive oil (EVOO) had a protective effect against Alzheimer's Disease (AD), and ultimately suggested that: “EVOO could be considered as a viable therapeutic opportunity for preventing or halting AD.” This promising clinical investigation helps support data from other studies (conducted on humans), that link olive oil consumption with the prevention of age-related cognitive decline. In a sub-study of PREDIMED, for example, researchers also noted that Mediterranean diet participants demonstrated better cognitive function than the folks on the Western (control) diet.
I could go on and on about olive oil and its polyphenol punch, but I think you get the idea. But before you run off to your local grocery store to stock up on it, there’s something you should know…
High-Quality Extra-Virgin Is the Way to Go
Polyphenol content in olive oil is determined by several factors, including climate, time of picking (unripe olives have more abundant polyphenols than ripe olives), and storage conditions (stainless steel or dark glass bottles are best). The variety of olives also matters.
If all this sounds confusing, there are really only a few simple things you need to be aware of when buying olive oil so that you end up with the best quality possible.
First, buy extra virgin or cold-pressed. Extra virgin olive oil is derived from the first pressing of the olives, making it more deeply hued, thicker, and tastier than refined olive oils. If you’re buying flavored olive oil, make sure it is cold-pressed (flavored olive oils cannot be called extra virgin because of the flavor addition). You want a minimally-processed oil because research shows up to 80 percent of the phenolic compounds are destroyed in the refining process. (As a side, be sure to use extra virgin olive oil for salad/vegetable garnishing or in marinades, not just for cooking. High heat can destroy polyphenols, and excessive heat can even result in dangerous compounds.)
Second, make sure it is sold in a dark glass bottle. If you’ve ever had the privilege of shopping at a gourmet olive oil store, you’ve probably seen that their oils are stored in big stainless steel vats. They’re able to pour the oil directly into dark glass bottles and seal them for you. Both measures ensure that the polyphenols and the overall freshness of the oil are protected.
An olive oil’s flavor can also tell you something about its polyphenol content. If the oil goes down smooth and without much flavor or “bite,” it is probably on the lower end. But if the taste is strong, bitter, even “spicy” or “peppery”—or if your throat feels a little tingly after you swallow—you’ve picked a good oil. These characteristics are all hallmarks of rich polyphenol content. The polyphenol bite may take some getting used to when you first try it. At an olive oil tasting in California, the peppery taste of olive oil had me coughing until I fully understood how to properly taste and evaluate it!
The moral here is, you cannot go wrong with adding high-quality extra virgin olive oil to your diet. Your heart (and every other part of your body) will thank you for it.
- Pérez-Jiménez J, et al. Identification of the 100 richest dietary sources of polyphenols: an application of the Phenol-Explorer database. Eur J. Clin Nutr. 2010 64, S112–S120. doi:10.1038/ejcn.2010.221
- Tuck KL and Hayball PJ. Major phenolic compounds in olive oil: metabolism and health effects. J Nutr Biochem. 2002 Nov;13(11):636–44. Last accessed Feb. 27, 2018.
- Mohamed Saleem TS and Darbar Basha S. Red wine: a drink to your heart. J Cardiovasc Dis Res. 2010 Oct–Dec;1(4):171–6. Last accessed Feb. 27, 2018.
- Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet (PREDIMED). N Engl J Med, 2013; 368:1279–90. Last accessed July 20, 2o2o.
- Bendinelli B, et al. Fruit, vegetables, and olive oil and risk of coronary heart disease in Italian women: the EPICOR study. Am J Clin Nutr. 2011 Feb;93(2):275–83. Last accessed March 2, 2018.
- Camargo A, et al. Gene expression changes in mononuclear cells in patients with metabolic syndrome after acute intake of phenol-rich virgin olive oil. BMC Genomics, 2010; 11:253.
- Samieri C, et al. Olive oil consumption, plasma oleic acid, and stroke incidence: the Three-City Study. Neurology. 2011 Aug 2;77(5):418–25. Last accessed March 2, 2018.
- Omar SH. Cardioprotective and neuroprotective roles of oleuropein in olive. Saudi Pharm J. 2010 Jul;18(3):111–21. Last accessed March 2, 2018.
- Zrelli H, et al. Hydroxytyrosol reduces intracellular reactive oxygen species levels in vascular endothelial cells by upregulating catalase expression through the AMPK-FOXO3a pathway. Eur J Pharmacol. 2011 Jun 25;660(2–3):275–82. Last accessed March 2, 2018.
- Gonzalez-Santiago M, et al. One-month administration of hydroxytyrosol, a phenolic antioxidant present in olive oil, to hyperlipidemic rabbits improves blood lipid profile, and antioxidant status and reduces atherosclerosis development. Atherosclerosis. 2006 Sep;188(1):35–42. Last accessed March 2, 2018.
- Lauretti, E., Iuliano, L. and Praticò, D. Extra-virgin olive oil ameliorates cognition and neuropathology of the 3xTg mice: role of autophagy. Ann Clin Transl Neurol. 2017 4: 564–574. doi:10.1002/acn3.431.
- Martínez-Lapiscina EH, Clavero P, Toledo E, et al. Mediterranean diet improves cognition: the PREDIMED-NAVARRA randomised trial. J Neurol Neurosurg Psychiatry. Published Online First: 13 May 2013. doi: 10.1136/jnnp-2012-304792.
- Owen RW, et al. Phenolic compounds and squalene in olive oils: the concentration and antioxidant potential of total phenols, simple phenols. Secoiridoids, lignans and squalene. Food Chem Toxicol. 2000 Aug;38(8):647–59. Last accessed March 2, 2018.