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