September 09, 2006
Many consumers worried about their health tend to want to deconstruct a healthy diet and ask what single components can be taken as an extract or pill. The heart healthy Mediterranean diet has been found to be high in antioxidant B vitamins. But a recent study showed that just taking B vitamins does not have the same effect. Adding vitamins actually increased the risk of a heart attack. The foods must be consumed whole to get the beneficial effect of the vitamins.
An article in the September 2006 issue of the Annals of Internal Medicine asked a similar question; are some of the benefits of eating a Mediterranean diet due to the oleic acid in olive oil or must you eat a whole food product such as a virgin oil which has its many accompanying antioxidants? The conclusions put any controversy about that to bed: "Olive oil is more than a monounsaturated fat. Its phenolic content can also provide benefits for plasma lipid levels and oxidative damage." The more phenols the oil had, the more healthful it seemed to be.
The Study; How is was done
The study involved 6 research centers from 5 European countries ; the Eurolive study group. The study was a randomized, crossover, controlled trial; statistically the strongest type of study to confirm the findings. Three oils were prepared. A virgin olive oil was picked which had a high concentration of polyphenols (366 mg/kg). Refined olive oil was then made from the same olives. The refining essentially removed all the polyphenols (2.7mg/kg). This oil was then adjusted to have the same vitamin E, vitamin C, beta carotene, saturated and polyunsaturated content. An oil with medium concentration of polyphenols (164 mg/kg) was made by mixing the first two.
The participants consumed 25ml per day of one of the three oils in replacement of other raw fats for 3 weeks. Urine samples were tested for substances in olive oil to see if the olive oil was actually consumed. Blood levels of glucose, cholesterol and a variety of biomarkers of oxidative damage from lipids (can you say 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride?) were measured. The study subjects ate no olive oil for two weeks then repeated the cycle with another of the study oils.
The conclusions
A daily 25ml dose of all three olive oils (the U.S. Food and Drug Administration recommendation) improved the ratio of good cholesterol to bad and improved triglyceride levels.
The higher the phenol content of the oil, the higher the HDL "good" cholesterol and the higher the level of antioxidants in the blood. The antioxidants prevent damage to LDL "bad" cholesterol and lowers the likelihood of clots in the blood vessels which can lead to heart disease.
Why this study is important
The study had good statistical power, it is not merely anecdotal. It was performed on humans, not lab animals or cell cultures. Virgin olive oil lowered known cardiovascular risk factors but because of the short time of the intervention, the study could not prove that people who eat olive oil have fewer heart attacks, strokes and other cardiovascular diseases.
Which olive oils have high polyphenols?
The health conscious will want to know which olive oil has the highest polyphenols. Phenol content is determined by olive variety, time of picking, olive condition and processing method, whether the oil is refined and the length of time the oil has been stored.
Variety - Specific types of olives, such as the Tuscan varieties (Frantoio, Coratina, Lucca, Pendolino), will have higher polyphenol values. These oils are valuable in that when blended with a low polyphenol oil they will extend the shelf life by preventing rancidity.
Time of picking - Most olives picked earlier in the year will have more polyphenols. Olives picked later in the winter have fewer polyphenols and a more mellow taste. Polyphenol concentrations increase with fruit growth until the olives begin to turn purple then begins to decrease. Years ago farmers valued the more mellow taste and tried to wait to pick their olives but risked freezing or loss to the elements. Now the strong earlier harvest taste has become popular.
Olive Condition - Picked olives which sit for more than 24 hours before processing start to lose antioxidants. Bruised olives or olives damaged by the olive fly will have higher acidity and lower antioxidants.
Processing method - Much is made of how the type of olive oil machinery will affect the flavor of extra virgin oil but in reality if used properly it has only a small influence. Extra virgin olive oil is made the same way with the same machinery in the US as in Italy. Mixing the olive paste in the presence of the oxygen in air will lower the polyphenols. For that reason stone mills, with their large surface area, can reduce polyphenol levels. Newer malaxation tanks that mix under a cover, a vacuum, or a blanket of inert gas claim to slightly raise polyphenols.
Most of the olive oil consumed in the US comes from Spain and Italy, and is usually refined. These mass market oils are much lower in phenols.
Refining takes olive oil which has already been made but which is old, rancid, was made from diseased olives or has some other sort of defect and makes it palatable. This is done by filtering, charcoal treatment, heating, and chemical treatment to adjust acidity. Refined oils are lower in tyrosol and other phenols. According to Wayne Emmons at Intertech, Extra Virgin Olive oil typically has 50-80 ppm polyphenols while refined oil has only 5 ppm.
Storage - As oil sits in storage tanks or the bottle, the polyphenols will slowly be oxidized and used up. This process speeds up when the oil is heated or exposed to light. If you want an oil with more polyphenols, buy one that displays a date guaranteeing that it is fresh and that has been stored properly.
Hydroxytyrosol and other phenols are not used in any legal definition so you can only make generalizations to how many there are in various types of oil. Oils labeled as "lite" or "light" refer to flavor, not caloric content, as all vegetable oils have the same amount of calories. Theoretically "light" could refer to an excellent extra virgin oil made from olives picked late in the year but usually it signifies a flavorless low quality (refined) oil from Italy or Spain.
If you want an oil high in polyphenols, pick one that is guaranteed to be extra virgin (has the COOC seal if produced in the US), is from the current harvest season and that has been properly stored. Some varieties have high polyphenols; Frantoio, Lucca, etc. Look for US oils made from these varieties or look in a quality store or deli for a high quality extra virgin oil made with care and well labeled.
Polyphenols in different olive oils - bragging rights.
As polyphenols become a household word, they are being seen on labels and websites. Apollo olive oil in Oregon House, California claims on the front page of their website up to 750mg/liter of polyphenols. That is about 675mg/kg, twice what the study used as its high polyphenol oil. To stay competitive more producers will start to brag about their polyphenol content. Oils which are higher in polyphenols tend to be harsher, more bitter and stronger flavored. Many consumers prefer a mellower oil made from olives which just don't have the same polyphenols. It would be a pity if the industry felt compelled to move toward these stronger oils for the polyphenol hype value.
Polyphenols in other foods.
One must look at the larger picture and examine the contribution of each food in the diet to polyphenols. If the oil in the study had 366mg/kg = 330mg/liter of polyphenols, then the 25cc recommended daily allotment adds just 8.25 mg of polyphenols to the diet.
Vegetables, legumes, fruits, tea, coffee, nuts, chocolate, wine and beer all add polyphenols. Comparing their values makes the debate a bit clearer.
Polyphenols in various foods:
500 mg in a tiny 40-g (about 1 oz.) square of dark chocolate
500 mg in two small cups of green tea
500 mg in a bowl of grapes
300 mg in a glass of red wine
Other foods producers are hip to the marketing potential of antioxidants. A box of Lipton tea now comes with a new line of bold text across the top: "175mg protective antioxidants naturally per serving"; more antioxidants in one cup of tea than a whole liter of an average extra virgin olive oil. There's even a new proprietary antioxidant logo that Unilever, owner of the brand, has created.
Other Antioxidants
Polyphenols are antioxidants common in oils but there are many water soluble antioxidants. The Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant contents in different foods. According to the FDA's Administrator Floyd P. Horn. "If these findings are borne out in further research, young and middle-aged people may be able to reduce risk of diseases of aging--including senility--simply by adding high-ORAC foods to their diets.
In the studies, eating plenty of high-ORAC foods:
- Raised the antioxidant power of human blood 10 to 25 percent
- Prevented some loss of long-term memory and learning ability in middle-aged rats
- Maintained the ability of brain cells in middle-aged rats to respond to a chemical stimulus--a function that normally decreases with age
- Protected rats' tiny blood vessels--capillaries--against oxygen damage" more
According to a recent Wikipedia entry, "a number of health food companies have capitalized on the ORAC rating, with dozens selling concentrated supplements that they claim to be "the number one ORAC product", some purporting that their supplements have a value of more than 25,000 ORAC units per 100 gram serving. It is not known whether such values are accurate or if such concentrated antioxidants can be absorbed by the human body as effectively as those found in natural foods."
Measuring Polyphenols Antioxidants
Olive oil has not traditionally been labeled with polyphenol content. The California Olive Oil Council requires testing for acidity and peroxide and an Ultra Violet Absorbency test. Most labs which test for acidity will also test for polyphenols. Several California mills have equipment to test polyphenols. As antioxidants become more of a marketing factor, producers may need to pay more attention to factors which enhance them. Having one's own electronic tester allows for some interesting experimentation. Producers can test the effect of olive variety, ripeness, harvest method, time to milling, milling method and pest infestation. Different oil batches could be blended to optimize antioxidants. Planting decisions could be changed depending on results. See testing equipment for prices on a typical setup.
Conclusion:
Producers of olive oil should be proud of their healthful product and may want to promote antioxidants. There are probably many other healthy components of olive oil and the Mediterranean diet which we have not discovered. By buying a whole food such as virgin olive oil you will probably be getting at least 100 times more polyphenols than pure or refined olive oil or most seed oils. Buying one which has the right type of olives may double your polyphenols from there, but you may not like the flavor of a Tuscan variety or early harvest oil. Olive oil is just one food in the diet - remember what your mother told you, eat your fruits and vegetables (and have a cup of green tea and a bit of chocolate for dessert).
Annals of Internal Medicine p 333 volume 145 number 5 September 5 2006