Olive Oil, a Health & Longevity Food | Plus: Frying With the Right Oils, Quickly + Discontinuously not Half as Hazardous for Your Heart, Pancreas & Waist as Previously Thought

If the frying time is short (2-5 min) and the heat not extreme, it's no problem to fry with virgin olive oil. If that's not the case there are better options.

You will probably remember my Facebook post about olive oil having recently become the first food that may officially call itself heart healthy in the European union. As María-Isabel Covas et al. point out in their latest paper, this leave a key question for the consumer unanswered: Which olive oil is the for you and your health? And how strong is the evidence it's actually going to make a sign. health difference (Buckland. 2015)?

In today's SuppVersity article I am going to answer these question and then turn to another, related issue: The alleged health-hazards of cooking and frying with vegetable oils as they were reviewed by Carmen Sayon-Orea (2015) and Carmen Dobarganes (2015):

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• Does it have to be virgin olive oil and how significant are the health benefits? The data from the EUROLIVE longterm study (Cicero. 2005) is unquestionably one of the more convincing arguments in favor extra virgin vs. regular olive oil (VOO). In said study 200 individuals from five European countries were randomly assigned to receive 25 ml/d of three similar olive oils, but with differences in their phenolic content (from 2.7 to 366 mg/kg of olive oil). The oil was administered in intervention periods of 3 weeks preceded by 2-week washout periods and the differential effects on important health markers were compared.
  
  What the authors found was that all olive oils increased HDL-cholesterol and the ratio between the reduced and oxidised forms of glutathione, but only the consumption of medium- and high-phenolic content olive oil (as you would buy it as "virgin olive oil" and "extra virgin olive oil" on the market) decreased lipid oxidative damage biomarkers such as plasma oxidised LDL, un-induced conjugated dienes and hydroxy fatty acids, without changes in F2-isoprostanes.
  

  

  Figure 1: Reduction in oxidized LDL in the PREDIMED study on Traditional Mediterranean Diet (TMD) with either virgin olive oil or nuts as one of the dietary sources of fat vs. recommended low fat diet (Fito. 2014).

  As Covas et al. (2015) point out, the scientists who conducted this larg-scale trial also found that the increases in HDL-cholesterol and the decrease in the lipid oxidative damage were linearly linked to the phenolic content of the olive oil the subjects consumed" (Covas. 2015)
  

  

  Table 1: Randomised, controlled studies on the effect of VOO on inflammatory markers (Covas. 2015)

  Even if we didn't have all the "Mediterranean diet studies" and the host of studies confirming the potent anti-inflammatory effects of virgin olive oil (see Table 1), the result of this well-controlled large-scale intervention alone would be quite convincing. In conjunction with the more recent PREDIMED study (Martínez-González. 2014; Fitó. 2014), however, the argument in favor of "virginity" (for olive oils ;-) becomes even stronger. An analysis of the PREDIMED study revealed that the beneficial effects of a Mediterranean style diet on LDL oxidation are most pronounced if extra virgin olive oil (with a high phenolic content of 316 mg/kg). With the EVOO version neither the "nutty" Mediterranean diet nor the still recommend low fat diet could compete (see Figure 1).
  

  

  Figure 2: The association between olive oil consumption (quartiles (Q) and per 10 g/d) and (a) overall mortality and cause-specific mortality ((b) CVD mortality, (c) cancer mortality and (d) other causes of mortality) in the European Prospective Investigation into Cancer and Nutrition Spanish cohort study (Buckland. 2015).

  The question you may still want to ask, though, is probably: "Are these markers actually relevant for my health?" Well, I guess we can hardly tell for sure what it is that mechanistically reduces the risk that you will die before your time, but the existing epidemiological data in Figure 2 leaves little doubt that the health benefits of consuming virgin olive oil can make the difference between life and death.
  
  So again, which oil do you use? The "extra virgin" among the olive oils, obviously. After all, EVOO has shown to promote additional benefits to those provided by regular olive oil and the few alternative vegetable oils. Effects of which Covas et al. point out that they are mediated by EVOO induced increases in the antioxidant content of LDL, nutrigenomic effects, and the modulation of atherosclerosis-related genes towards a protective mode.
• Does cooking and frying with vegetable oils kill? I have been addressing this issue shortly in my articles on the problems that arise with cooking with lard and tallow (read it) and my article about the "best" cooking oils (read it), but since we are already talking "oils" - in this case "olive oils" - it may be worth taking a look at two recent papers by Dobarganes et al. (2015) and Sayon-Orea et al. (2015).
  

  

  Table 2: Overview of the various substrates of vegetable oil and their effects in different experimental models as summarized by Dobarganes and Márquez-Ruiz (2015).

  In their latest review Dobarganes and Márquez-Ruiz list a whole host of processes and scientific evidence that (a) proves that there can be health hazardous compounds that form when you cook thermally unstable vegetable, that (b) these compounds are readily absorbed by mouse and man and that (c) even the relatively "small" amount that is found in industrially produced fried foods can be a threat to our health if we consume them in excell (see Table 2).
  
  

  

  Figure 3: Odds and hazar ratios and 95 % CI for the fully adjusted model in the studies included in Sayon-Orea's 2015 systematic review. * Fried food consumption as exposure. † Olive oil consumption as exposure. ‡ Sunflower oil consumption as exposure. § Palm oil consumption as exposure.

  This does not mean, though, that you will drop dead from the occasional serving of French fries - and that despite the existing evidence that some compounds that form during frying can impair the nutritional value of food or be potentially harmful. If you look closely at the time and heat it takes for the bad byproducts of cooking and frying to arise, it is evident that it's not you, but rather the food industry and restaurants with their high temperatures and cooking times that are to blame for the problems. They are the ones using the "discontinuous frying process" of which Dobarganes and Márquez-Ruiz say that only they allow frying oils to reach "degradation levels much higher than that established for human consumption" (Dobarganes. 2015).
  
  It is thus hardly surprising that Sayon-Orea et al.'s systematic review disproves the myth "that frying foods is generally associated with a higher risk of CVD" (Sayon-Orea. 2015 | my emphasis). Furthermore the authors analysis of the existing evidence indicates that cooking and frying with the previously praised virgin olive oil, in particular, is actually with a significantly reduced risk of CVD clinical events (see Figure 3).
  
  At this point it may be worth pointing out that this review has a small selection bias. If you look at the correlates in studies that are not as specifically interested in fried foods as the one reviewed by Sayon-Orea, but rather at food choices in CVD patients or diabetics there are positive correlations, correlations with "junk food", if you will. Therefore we can assume that any association between fried food consumption and cardiovascular disease (CVD) risk is probably mediated by the potentially obesogenic effect of certain types fried foods. Foods that are usually of overall low nutritive, but high caloric value - specifically if they are produced industrially or by fast food restaurants.
  
  If you are frying your foods at home, use oils with high amounts of unsaturated fast like virgin olive oil (or alternatives for longer frying durations and higher temperatures) and don't start frying snickers or ice-cream (as seen on TV ;-), frying your foods may actually be way less hazardous than many of you probably thought.

So what did you learn today? The health benefits of olive oil are not only, but largely dependent on its polyphenol content. From previous SuppVersity articles, you will know that those can be damaged by cooking and frying, but low cooking temperatures and short frying times minimize the risk of (a) missing out on all the polyphenol action in virgin olive oil and (b) allowing too many of the health hazardous metabolites of high PUFA oils - don't forget that olive oil still contains relatively high amounts of omega-6s - to rise.

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Thus, unless you're a weak-willed victim of the food industry, your risk of dying from frying induced... ah, I mean from fried-food related heart disease is minimal. The same goes for your risk of obesity and diabetes... and let's be honest: Can you imagine a "Mediterranean Diet" (MeD) without tons (and I mean "tons") of fried foods? I can't. What I can imagine, though, is that the use of heat stable (virgin olive) oils, discontinuous frying to ensure overall short frying times, as well as frying healthy not junk food (mostly unbreaded meats and veggies) make the health-relevant difference between the effect of fried foods in the MeD and those from the Standard American Diet, which are usually fried discontinuously in less heat stable oils  | Comment! 

References:

• Buckland, Genevieve and Carlos A. Gonzalez. "The role of olive oil in disease prevention: a focus on the recent epidemiological evidence from cohort studies and dietary intervention trials." British Journal of Nutrition 113 (2015): pp S94-S101. 
• Cicero, Arrigo FG, et al. "Changes in LDL fatty acid composition as a response to olive oil treatment are inversely related to lipid oxidative damage: The EUROLIVE study." Journal of the American College of Nutrition 27.2 (2008): 314-320.
• Covas, María-Isabel, Rafael de la Torre and Montserrat Fitó "Virgin olive oil: a key food for cardiovascular risk protection." British Journal of Nutrition 113 (2015): pp S19-S28. 
• Dobarganes, Carmen and Gloria Márquez-Ruiz "Possible adverse effects of frying with vegetable oils." British Journal of Nutrition 113 (2015): pp S49-S57. 
• Fitó, Montserrat, et al. "Effect of the Mediterranean diet on heart failure biomarkers: a randomized sample from the PREDIMED trial." European journal of heart failure 16.5 (2014): 543-550.
• Martínez-González, Miguel Á., et al. "Extra-virgin olive oil consumption reduces risk of atrial fibrillation: the PREDIMED trial." Circulation (2014): CIRCULATIONAHA-113.
• Sayon-Orea, Carmen, Silvia Carlos and Miguel A. Martínez-Gonzalez "Does cooking with vegetable oils increase the risk of chronic diseases?: a systematic review." British Journal of Nutrition 113 (2015): pp S36-S48.