by Craig Weatherby
In a recent article on the Huffington Post, nutritionist Linda Bergersen reported the results of a study testing the blood chemistry and blood flow effects of various fats.
Ms. Bergersen characterized the small, 10-year-old study as “recent” …having apparently missed or misread its November 1, 2000 publication date.
And she exaggerated the meaning of its key outcome… namely, that two different meals featuring extra virgin olive oil reduced blood flow after a meal by 10 and 31 percent respectively.
First, this drop was not a stark contrast to a flow reduction of 10 percent following a meal featuring canola oil.
And this difference means much less than it seems in the context of ample clinical evidence documented substantial artery-health benefits from extra virgin grade olive oil.
Ms. Bergersen’s error in calling the 2000 study “recent” may be no big deal in itself.
However, she failed to mention the many clinical findings showing positive artery-health effects from EV olive oil… all published during the intervening decade.
These include a three-year-old clinical study in diabetics, in which blood flow did not drop significantly after a meal rich in monounsaturated fatty acids (MUFA) from olive oil, but did decline significantly after a meal rich in saturated fat (Tentolouris N et al. 2008).
Decade-old study found EV olive oil reduced blood flow more than canola or salmon
Here’s a quick summary of the tiny clinical study Ms. Bergersen reported, and our analysis of its meaning.
The researchers fed 10 healthy subjects five different meals, each containing 900 calories and 50 grams of fat.
Canola oil (50 g) and whole grain bread (120 g)
Canned sockeye salmon (420 g) and crackers (30 g)
Extra-virgin olive oil (50 g) and whole grain bread (120 g)
Extra-virgin olive oil (50 g), whole-grain bread (120 g), and vitamins C (1 g) and E (800 IU)
Extra-virgin olive oil (50 g), whole-grain bread (120 g), balsamic vinegar (100 ml), and a salad with romaine lettuce, carrot and tomato.
Before each meal, and again three hours after it, the researchers measured the participants’ blood levels of sugar, cholesterol, and fat (triglycerides)… as well as a measure of blood flow called brachial artery flow-mediated vasodilation (FMD).
All five meals raised blood triglycerides significantly—probably due in part to the bread and crackers—but did not change cholesterol or sugar levels much.
The olive oil + bread meal reduced FMD 31 percent, while the olive oil + vinegar/salad meals and canola oil + bread meals both reduced FMD by 10 percent (The salmon + crackers meal reduced FMD by just 2.3 percent).
The authors’ conclusions are basically sound:
“In terms of their postprandial [after-meal] effect on endothelial [artery] function, the beneficial components of the Mediterranean and Lyon Diet Heart Study diets appear to be antioxidant-rich foods, including vegetables, fruits, and their derivatives such as vinegar, and omega-3-rich fish and canola oils.
But one outstanding error in their statement is to lump fish and canola oils together as “omega-3-rich.”
Fatty fish such as salmon are indeed very rich in the long-chain omega-3s (EPA and DHA) our cells actually absorb and use functionally – which are the only kind associated with serious heart health benefits.
In contrast, canola oil contains modest amounts of the short-chain omega-3 called ALA, only about five percent of which the body converts into EPA and DHA.
More importantly, there’s abundant lab and clinical evidence that extra virgin olive oil benefits artery health in ways likely to help deter cardiovascular disease.
Many studies show artery benefits from EV olive oil’s antioxidants
For a fuller picture of the heart benefits of extra virgin grade olive oil see the “Olive Oil & Other Oils” section of our news archive.
(Why put “antioxidant” between quotes? Polyphenols’ many apparent health benefits in humans appear to flow from their “nutrigenomic” effects on gene expression, rather than the direct antioxidant effects seen in test tube experiments.)
A team in Barcelona tested the effects of olive oil phenols on three key risk factors in disease among 549 healthy men from five European countries:
- blood levels of triglycerides
- blood levels of cholesterol, and 3) damage to blood lipids (cholesterol oxidation) and arterial tissues from free radicals… so-called “oxidative stress.”
They divided the volunteers into three groups, each of which was instructed to replace their usual cooking oils (e.g., canola, soy, corn) and condiment fats (e.g., butter, margarine) with just under one ounce per day (25 mL) per day of one of three olive oils.
Each group’s olive oil contained a different level of phenolic antioxidants, measured as milligrams per kilogram (mg/kg)
Low phenol level (2.7 mg/kg, as in a cheap, refined “pure” grade oil)
Medium phenol level (164 mg/kg, as in a “virgin” grade oil)
High phenol level (366 mg/kg, as in an “extra virgin” grade oil)
After the first three weeks, each group switched to one of the other oils for another three weeks. (To eliminate any possible effects from prior consumption of olive oil, each of the two oil-consuming periods in this “crossover” trial was preceded by two weeks of abstinence from olive oil.)
The researchers checked adherence with the regimen by testing the participants’ urine for signs of the main phenols in olive oil (tyrosol and hydroxytyrosol), and found compliance good across the board.
In the end, the results were clear, with two out of three of the observed beneficial effects linked closely to the widely divergent phenol contents of the different grades of olive oil consumed by each of the three test groups:
The high-phenol (i.e., extra virgin) olive oil outperformed the other two oils (virgin and pure grade) when it came to enhancing three factors helpful to cardiovascular health:
Healthiest cholesterol ratios (i.e., lowest total cholesterol in relation to “good” HDL cholesterol).
Biggest rise in “good” HDL cholesterol
Biggest drop in levels of oxidized LDL cholesterol
All three oils reduced subjects’ triglyceride levels
The monounsaturated fat (oleic acid) in olive oil tends to reduce LDL oxidation, and may have been partly responsible for that effect. And the drop in triglycerides seen with all three grades suggests that monounsaturated oleic acid—found at equal levels in all olive oils—is largely responsible for that effect.
As the Barcelona team concluded, “Olive oil is more than a monounsaturated fat. Its phenolic content can also provide benefits for plasma [blood] lipid [triglyceride/cholesterol] levels and oxidative damage.”
So we welcome Ms. Bergersen’s timing error because it gave us a chance to clarify the situation, and set the record straighter!
Bergersen LL. Report Questions Health Benefits of Olive Oil. February 1, 2011. Accessed at http://www.huffingtonpost.com/linda-larrowe-bergersen/olive-oil-health_b_816011.html
Covas MI, de la Torre K, Farre-Albaladejo M, Kaikkonen J, Fito M, Lopez-Sabater C, Pujadas-Bastardes MA, Joglar J, Weinbrenner T, Lamuela-Raventos RM, de la Torre R. Postprandial LDL phenolic content and LDL oxidation are modulated by olive oil phenolic compounds in humans. Free Radic Biol Med. 2006 Feb 15;40(4):608-16. Epub 2005 Oct 18.
Covas MI, Nyyssonen K, Poulsen HE, Kaikkonen J, Zunft HJ, Kiesewetter H, Gaddi A, de la Torre R, Mursu J, Baumler H, Nascetti S, Salonen JT, Fito M, Virtanen J, Marrugat J, EUROLIVE Study Group. The effect of polyphenols in olive oil on heart disease risk factors: a randomized trial. Ann Intern Med. 2006 Sep 5;145(5):333-41.
Karatzi K, Papamichael C, Karatzis E, Papaioannou TG, Voidonikola PT, Vamvakou GD, Lekakis J, Zampelas A. Postprandial improvement of endothelial function by red wine and olive oil antioxidants: a synergistic effect of components of the Mediterranean diet. J Am Coll Nutr. 2008 Aug;27(4):448-53.
Marrugat J, Covas MI, Fito M, Schroder H, Miro-Casas E, Gimeno E, Lopez-Sabater MC, de la Torre R, Farre M; SOLOS Investigators. Effects of differing phenolic content in dietary olive oils on lipids and LDL oxidation--a randomized controlled trial. Eur J Nutr. 2004 Jun;43(3):140-7. Epub 2004 Jan 6.
Tentolouris N, Arapostathi C, Perrea D, Kyriaki D, Revenas C, Katsilambros N. Differential effects of two isoenergetic meals rich in saturated or monounsaturated fat on endothelial function in subjects with type 2 diabetes. Diabetes Care. 2008 Dec;31(12):2276-8. Epub 2008 Oct 3.
Vogel RA, Corretti MC, Plotnick GD. The postprandial effect of components of the Mediterranean diet on endothelial function. J Am Coll Cardiol. 2000 Nov 1;36(5):1455-60.
Weinbrenner T, Fito M, de la Torre R, Saez GT, Rijken P, Tormos C, Coolen S, Albaladejo MF, Abanades S, Schroder H, Marrugat J, Covas MI. Olive oils high in phenolic compounds modulate oxidative/antioxidative status in men. J Nutr. 2004 Sep;134(9):2314-21.
Weinbrenner T, Fito M, Farre Albaladejo M, Saez GT, Rijken P, Tormos C, Coolen S, De La Torre R, Covas MI. Bioavailability of phenolic compounds from olive oil and oxidative/antioxidant status at postprandial state in healthy humans. Drugs Exp Clin Res. 2004;30(5-6):207-12.
Vázquez-Velasco M, Esperanza Díaz L, Lucas R, Gómez-Martínez S, Bastida S, Marcos A, Sánchez-Muniz FJ. Effects of hydroxytyrosol-enriched sunflower oil consumption on CVD risk factors. Br J Nutr. 2010 Dec 8:1-5. [Epub ahead of print]