Olive Oil: The Good, the Bad & the Ugly

Dr. Sears and Olive Oil Blog

Olive oil can be considered the first nutrition supplement since its first use more than 6,000 years ago. We now know the reason: the polyphenols.

The Good – Olives Contain Unique Anti-Inflammatory Properties

Olives are a fruit, not a seed. As a result, it contains unique types of polyphenols not found in other fruits and vegetables. Tyrosol, hydroxytryrosol, oleocanthal and oleuropein each provide unique anti-inflammatory properties. This is why olive oil was so prized in the ancient world and remains an integral component of the Mediterranean diet. That’s the good.

The Bad – The Impact of Pesticides

Polyphenols are the reason that olive oil has health benefits for humans, but they have even greater health benefits to the olive fruit itself. It is polyphenols that protect plants from microbial attack. Once you start using pesticides to increase production, the plants generally decrease the product of polyphenols since it requires a lot of energy to produce them. This effect is more profound in fruits than vegetables.

However, not all conventionally grown fruits and vegetables have high levels of chemical residues. It really depends on how they are farmed. The following table outlines these varying levels of chemical residues in conventional fruits and vegetables.

Most Commonly ContaminatedModerate Commonly ContaminationLeast Commonly Contaminated
  • Apples
  • Celery
  • Strawberries
  • Peaches
  • Spinach
  • Nectarines
  • Grapes-Foreign
  • Sweet Bell Peppers
  • Potatoes
  • Blueberries
  • Lettuce
  • Kale/Collard Greens
  • Green Beans
  • Summer Squash
  • Peppers
  • Cucumbers
  • Raspberries
  • Grapes – Domestic
  • Plums
  • Oranges
  • Cauliflower
  • Tangerines
  • Bananas
  • Winter Squash
  • Cranberries
  • Onions
  • Sweet Corn
  • Pineapples
  • Avocado
  • Asparagus
  • Sweet Peas
  • Eggplant
  • Cantaloupe
  • Kiwi
  • Cabbage
  • Sweet Potato
  • Grapefruit
  • Mushrooms

What about olives?

Although many olive growers don’t use herbicides or pesticides, you never really know those who do. Finding certified organic extra-virgin olive oil is always your best bet for maximum polyphenol content. More importantly, the taste of organic olive oil is always significantly better than conventional olive oils.

The Really Ugly – Your Olive Oil May Be Faking It

Since olive oil is valuable, it is likely to be adulterated by adding other inferior substances. This was a problem in even ancient Roman times where containers were stamped with official seals to make it difficult to adulterate the oil.

Today, the problem is far more widespread with nearly 70% of extra-virgin oil olive being sold in the U.S. having been adulterated.

Harvesting Perfect Olives

What’s a consumer to do in a world of pesticides and adulterated olive oil?

It has to taste great (which it does) and be rich in polyphenols (that we analyze in every lot, because like Fox Mulder of the X-Files says: “we trust no one”).

I searched out the few organic cooperatives in Italy making high quality extra-virgin olive oil.  Then, we harvested in late fall, followed by processing over the winter. Then the various processed lots were tested for polyphenol content. Those lots that met our polyphenol requirements were bottled and brought to the U.S. under the Zone brand. We purchased the entire year’s production that met our quality standards. It wasn’t much, but those olives made about 190 cases worth of Dr. Sears’ Zone Extra Virgin Olive Oil. And we have it all.

Branding is crucial. With my Zone Extra-Virgin Olive Oil, you can have the ideal anti-inflammatory condiment for every meal – at least while it lasts. As of today, we have less than 100 cases of Dr. Sears’ Zone Extra Virgin Olive Oil remaining in stock. Order yours today.


  1. Faller ALK and Fialho E. “Polyphenol content and anti-oxidant capacity in organic and conventional plant foods.” J Food Composition and Analysis 23: 561-568 (2010).
  2. Muller T. Extra Virginity: The Sublime and Scandalous World of Olive Oil. W.W. Norton. New York, NY (2013).
  3. Blechman N. “Extra virgin suicide: The adulteration of Italian Olive Oil.

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About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 45 years to the study of lipids. He has published 40 scientific articles and holds 14 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 14 books, including the New York Times #1 best-seller, The Zone, which have sold more than 6 million copies in the U.S. and have been translated into 22 different languages.


  1. R.G

    Hello Dr Sears,

    I have been searching for the light to lead me out of nutrition darkness for years. Massive confusion and deception exists in the world of nutrition as well as supplements.Your honest and brilliant message has changed my life and I’m sure tens of thousands more who are smart enough to listen to your message. My massive inflammation and high ferritin levels are finally under control. Also my family and children will benefit from your wisdom. Thank you very much for all you have given the human race. God bless you.

  2. Dorothy Nyabiosi

    thank you for all insightful comments. Thanks for prompt response.

    Just wondering how the negatively charged ionized alkaline water plays part in the nutrition.

    • Dr. Sears

      Probably not as the alkaline water would be quickly neutralized by stomach acid. On the other hand, the release of oxygen from the red blood cell is optimal at a slightly alkaline pH (7.35 to be exact) in the blood. The best way to maintain a slightly alkaline pH of blood is to make sure you consume primarily fruits and vegetables and highly restrict grains and starches as carbohydrates sources since grains and starches generate acid responses. Although protein can produce a slight acidic effect during metabolism, as long as you are consuming more fruits and vegetables than protein, the appropriate alkalinity of the blood is maintained in addition to having better hormonal control.

  3. Cathy Goldstein


    Some tips on buying high quality extra virgin olive oil unadulterated with low end toxic oils: after selecting an organic extra virgin olive oil look on the back or bottom of the label. It should say made from 100% organic extra virgin olives. Seems obvious but onces you start looking it is amazing how many do not have this.

    • Dr. Sears

      Even if has an organic label, still give it taste taste for the buttery taste on the tip of tongue and peppery taste when you flip it to the back of the mouth.

  4. Daniel

    I am struggling with a high acid level in my blood. Will olives as well as the oil reduce the acid level?

    • Dr. Sears

      High levels of acid in the blood is usually the consequence of either (1) the excess consumption of excess grains and protein or (2) the under-consumption of fruits and vegetables. Once you balance your meals with the appropriate combinations of each as described on our Zone Diet site, you should solve your blood acid problems.

  5. BJ

    Dr. Sears,

    One other question: have you compared the phytochemical contents of olive oils from different regions? I ask because I’m in California, where olive estates abound. I’ve found that, taste-wise, Californian olive oil is not very flavorful (not to me), especially not compared to Italian oils, but as to nutrient composition I can’t say.

    • Dr. Sears

      I totally agree with your assessment of olive oil from California. It takes at least 50 years for an olive tree to mature and bear excellent fruit. I have not made an analysis on the total polyphenol content nor the actual individual breakdown of polyphenols in California olive oils, but I imagine they will not be as complex as Italian varieties because of the lack of maturation of the trees themselves. Unlike wine-making whether advances in technology can improve flavor, the production of olive oil depends primary on the quality of the tree and the care in the removal of the olives, not the technology to process the oil.

  6. BJ

    Hello Dr. Sears,

    Do you provide a quantification of the polyphenol content in your olive oil? If so, which polyphenols? Do you have a reference range for therapeutical doses of the different olive polyphenols? 20mg of oleuropein isn’t the same thing as 20mg of hydroxytyrosol.

    FYI, there’s another brand of olive oil on the market that claims to have 30 times the hydroxytyrosol content compared to “normal” olive oil. You can check it out here, if you’re curious: http://www.olivie.ma/en/olivie-plus.html

    I’ve tried it, and it is grassy in flavor (which I really don’t find palatable…I prefer buttery), and very bitter (which I assume is due to the hydroxytyrosol, so is a good thing) but without any pepperiness. As I understand it, pepperiness in olive oil is due to the oleocanthal, and is important since, among other things, it can inhibit the COX-2 enzyme. Most research that I’ve read indicates that polyphenols are more effective in combination than isolated (such as those found in the various products of the olive tree), so if the lack of pepperiness means little to no oleocanthal I’d say it’s not worth the cost.

    However, as far as oleocanthal, it appears that olive oil marketers may try to mask the true low quality nature of their product by adding synthetic oleocanthal: http://www.oliveoiltimes.com/olive-oil-health-news/patent-bid-showcases-oleocanthals-versatility/36195

    I know that I’ve been frustrated over the years at the difficulty of finding good extra virgin olive oil, especially on a consistent basis. I feel that a concentrated extract would be ideal (perhaps this is something you can pursue?). Most olive supplements on the market are extracts of the leaf and standardized for oleuropein, which isn’t nearly as powerful an antimicrobial or free radical scavanger as hydroxytyrosol (which is both bactericidal and fungicidal). There is one olive leaf extract standardized for hydroxytyrosol, but none of the other olive constituents: https://www.prohealth.com/shop/product.cfm/product__code/PH398

    For the time being, I consider high quality extra virgin olive oil to be one of the most versatile and important supplements one can take, with an emphasis on high quality. Since we can’t rely on the organoleptic properties of the oil to determine its value, it’s even more important that the quality (polyphenols, etc) be quantified. It will be more expensive but totally worthwhile (within reason).

    Thank you for your time.

    • Dr. Sears

      First these are excellent and insightful questions.

      The polyphenol content of our current lot of organic extra-virgin oil is 319 mg/kg. We have not done a complete analysis of the various polyphenol classes of this lot as it was the only one from the fall 2015 harvest from the cooperative that made our minimum polyphenol requirements.

      One can certainly fortify any olive product with additional ingredients like hydroxytrysol, but it would be still be considered adulterated since the added component is not naturally in the extracted olive oil and therefore has to labeled as a supplement, not a food. That’s why the adulterated extra-virgin olive oils do not have a buttery taste. Italy has developed a very extensive fatty acid testing establishment to protect their olive oil industry. In the U.S. we are nowhere as sophisticated (except perhaps for Zone Labs) in maintaining olive oil standards.

      Oleocanthal has a definitely pepper-like taste that can actually induce coughing, because it has anti-inflammatory properties as a weak non-specific inhibitor of COX enzymes (Beauchamp et al. Nature 437: 45 (2005). There is some indication that it may also inhibit mTOR activity (Khanfar et al Phototherapy Research 29:1776 (2015). However I believe it is the unique combination of polyphenols found in authentic extra-virgin olive oil that is truly the key to its health benefits.

      On the other hand, we have put great efforts in producing polyphenol extracts from the maqui berry and chocolate (MaquRx and CocacoRx (coming soon)) that are approved as GRAS status food additives that have removed heavy metal contaminants (such as cadmium) and have been tested clinically. The levels of polyphenols in these extracts is 40-50% of the total weight of the extract as compared to the 0.03% polyphenol content in extra-virgin olive oil.

      I believe it will be the combination of natural polyphenol sources such as organic extra-virgin olive oil coupled with highly purified polyphenol extracts (especially incorporated into unique food products) that will provide maximum health benefits. In the final analysis, it is the polyphenol dose that delivers the health benefits.

  7. Lloyd

    I know the answer to this is in one of your books but please describe what really high quality olive oil should taste like.

    • Dr. Sears

      Take a teaspoon of extra virgin oil and put it on the front tip of your tongue. It should taste like high-quality butter. Then flip the olive oil to the back of your throat with the tongue and you should experience a pepper-like sensation if not outright coughing. That comes from the polyphenols. You need both qualities for it to be considered a high-quality extra virgin olive oil.

  8. John

    The time between harvesting and consumption is also important, the fresher the better. When was this oil harvested/processed?

    • Dr. Sears

      The harvesting is done in late fall followed by processing the winter. Then the various processed lots have to be tested for polyphenol content. We only take those lots that meet our polyphenol requirements prior to bottling. Therefore all the olive oil was harvested in the fall in 2015. This means once these bottles are gone, the extra availability will be the harvest of 2016 ready for shipment in early 2017.

  9. lowell tyler

    regardless of adulterated or not, here is a little known fact about olive oil, which, is a very ‘healthy’ oil to consume, with this one important exception…olive oil reaching superheated temperatures–ie., if it starts emitting smoke at any stage of cooking, converts many of its good oils to carcinogens. in fact, overheated olive oil is more carcinogenic than most any other cooking oil. my wife loves to put it on chicken, beef, potatoes before grilling. not for me anymore. been through colon cancer once, gonna avoid any possible issues i can.

  10. margot

    Most corn in the USA is GMO…you should include GMOS on your list as well…since they were created with pesticides built in…Most informed people stay away form corn in the USA due to this unless they grow it themselves…several others on your list are GMO contaminated as well….PLEASE ADD THIS! Thanks!

    • Dr. Sears

      I was only focusing the listing in the table to different levels of herbicide and pesticide used in different non-organic ally grown fruits and vegetables. I would be more concerned about kale than corn.

    • Margaret Ringsred

      Margot, can you relay more info about how “pesticides are built into GMO” seeds? I had never heard this and wish to know more. Thank you, and in fact, if you can tell me how to make sure the corn I buy at the store is not GMO, I would appreciate that as well. I know GMOs are growing fast to takeover the universe of ag, but surely there must still be some large farming ops that have opted out? Thank you anyone who has good info on this.


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