The Quest for the Optimal Cooking Oil: Heat Stable, Low PUFA & Cholesterol Free - High MUFA Sunflower / Canola, Olive, Coconut & Avocado Oil Qualify for the TOP5

The oil is not he only thing that's damaged, when you're frying foods; and acrylamide is only the most prominent of these nasty compounds.

Alright, it's about time to acquit myself of a longstanding promise: the promise to finally write the unofficial second part to my article on cooking oils & fats from February 2014 that busted the myth of the "healthy" saturated cooking oils and fats (read more). It's an "unofficial" part II, because the previous article was actually intended to be "just" a rebuttal to the unwarranted craze about using butter, lard & co to fry in order to protect yourself from developing heart disease and other nasty ailments.
Before we delve deeper into the discussion lets briefly recap what exactly we are looking for in the "optimal" frying oil: The optimal frying oil should...

• ... either contain a low amount of readily oxidizable PUFAs or contain significant amounts of antioxidants that protect these important, but sensitive fatty acids from being oxidized,
• ... be cholesterol-free, because dietary cholesterol can be a problem, if it's consumed in large amounts in its pro-atherogenic (=tending to promote the formation of fatty deposits in the arteries) oxidized form,
• ... have a high smoke point, i.e. can be heated to very high temperatures before enough volatile compounds such as water, free fatty acids, and short-chain degradation products of oxidation emerge from the oil that a bluish smoke becomes clearly visible.

All three suppositions are important because, the consumption of oxidized PUFAs, oxidized cholesterol (Valenzuela. 2003) and other volatile compounds from "burnt" oils and fats have consistently been associated with negative health effects.

• Figure 1: The consumption of soy bean oil that was heated for 3h is associated with an increase in body fat that is independent of an increased intake of food (Penumetcha. 2013)

  The consumption of oxidized PUFAs has been associated with an increased cardiovascular disease risk and increases in body fat, of which recent studies indicate that it is not caused by an increase in food intake (Penumetcha. 2013).
  
  Some scientists in fact believe that the association between the consumption of high amounts of (high omega-6) seed oil is associated with heart disease & co not due to the fatty acid composition of these oils per se, but rather due to extensive use of these products in highly processed (convenient) foods, which in turn contain high amounts of oxidized polyunsaturated fatty acids and will thus drive the development of heart disease, diabetes & co.
• Oxidized cholesterol as it occurs at relatively high amounts un highly processed foods, has the potential cytotoxic, mutagenic, atherogenic, and possibly carcinogenic effects (Peng. 1985; Kumar. 1991; Valenzuela. 2003; Orczewska-Dudek. 2012). In that it's important to point out that not all heated animal products (e.g. eggs) will contain significant amounts of oxysterols, because the formation of these potentially unhealthy byproducts of the heating process depend on (a) temperature, (b) heating time and (c) storage & packaging.
  
  Against that background, soft-boiled eggs are healthier than hard-boiled eggs or fried eggs and a hot chocolate milk is less of a problem than repeatedly heated and extensively processed eggs, meats & co.
  

  Figure 2: Overview of the effects of storage, processing and heating on the levels of oxidized cholesterol in various food items (various sources).

  Why? Easy: They contain significantly lower amounts of the potentially unhealthy oxidized cholesterol - a dietary ingredient that can become a serious problem only if you consume high quantities on a regular basis, though.

• Figure 3: Changes occurring during deep fat frying (Fritsch. 1982).

  Oxidized fatty acids and cholesterol are actually part of the volatile compounds that arise, when a cooking / frying oil starts to "smoke". In his 1981 paper in the Journal of the American Oil Chemists’ Society, Fritsch published a neat graphical illustration of what happens during the frying process (see Figure 3).
  
  As you can see, it's a complex series of changes and reactions that produce numerous decomposition products. As Fritsch points out, "the functional, sensory and nutritional quality of frying fats are changed and may reach a point where high quality foods can no longer be prepared," as these reactions proceed. In the end, the oil will be unpalatable.
  
  Unfortunately, the negative effects on your health will occur way before you will be able to detect the changes in viscosity, color or taste (specifically if the oils are used in processed products, where any off tastes would be covered by (artificial) flavorings, anyways) or see the smoke. That's also why the smoke point of a given fat  / oil is not exactly the best criterion to judge its suitability as "optimal frying oil".

Now that you're aware that checking it's not enough to look at the "Smoke Point" in the unreferenced Wikipedia article, let's get to the question that's been praying on your minds ever since I posted my article on cooking oils & fats on February 2014 (read more): Which oil, if not the allegedly superior animal fats, shall I use for cooking and frying?

Q: What's the optimal frying oil, now? A: It depends!

Now that we know that we want an oil that's relatively low in PUFAs, high in (natural) antioxidants, cholesterol-free and has a high smoking point, a few candidates come to mind:

• High oleic acid canola (or rapeseed) or high oleic acid sunflower oil - Both contain a low amount of PUFAs, no cholesterol, and have relatively high a smoking points of 194°C  and 200°C, respectively.
  

  Table 1: Ranking of the oils tested by Bertrand Matthäus; 1 indicates rank #1 = first place, 4 indicates rank #4 = last place (Matthäus. 2006).

  Accordingly, it's not surprising that high oleic acid rapeseed and sunflower oils come out on top of a comparison by Betrand Matthäus, in which the researcher compared the formation of  oligomer triacylglycerols, polar compounds and free fatty acids, as well as the results of a sensory evaluation of the oil itself and the French fries that were fried with high oleic acid rapeseed (HORO), high oleic acid sunflower (HOSO), partially hydrogenated rapeseed oil (PHRO) and, the worst choice, palm olein (PO).
  
  If you compare the high oleic acid varieties of sunflower and rapeseed oil that are made from seeds with a low PUFA and high MUFA content, you will yet realize that the the often derided sunflower oil is actually the most stable one. The rapeseed oil, on the other hand, produced the tastiest fries (according to the full text of the study). Since "only small differences in the chemical parameters of all oils were found" and "[o]nly the total result of the assessment of PO was significantly worse than the results of the other oils (p < 0.01)" (Matthäus. 2006), the rapeseed oil comes out on top of this comparison.

• Now, being resistant to oxidation is one thing. Having overall beneficial effects on one's health, however, is a totally different thing. A "thing" that was tested in a 2005 study, by Allman-Farinelli et al. in which the researchers were able to show that replacing saturated fats in the diet with high-oleic-acid oils like sunflower oil will favorably alter the low-density lipoprotein cholesterol, triglycerides, and factor VII coagulant activity" of healthy men and women and thus present "another useful source of MUFA for diets aimed at prevention of heart disease"(Allman-Farinelli. 2005).
  

  Figure 4: Evidence of the effect of canola oil on health-related risk factors.

  In a similar vein, canola aka eruchic acid free rapeseed oil, which is also available as high oleic acid cooking oil, has been shown to reduce TC concentrations in healthy or hypercholesterolemic individuals, compared with high-SFA or typical Western diets. Studies also indicate that it "may potentially promote immune and cardiovascular health through its antithrombic and antioxidative effect" (Lin. 2013). For the other benefits listed in the overview in Figure 4, the results are sometimes less equivocal. Overall, Lin et al. whose review of literature was obviously funded by the canola industry still claims that "canola oil can now be regarded as one of the healthiest edible vegetable oils in terms of its biological functions and its ability to aid in reducing disease-related risk factors and improving health" (Lin. 2013) - a claim that sounds a bit hyperbolic, in spite of the fact that their review of the literature supports many of the claims.
  
  Against that background I would stick to using canola, or if you live in Europe or can acquire it overseas rapeseed oil only in its high oleic acid variety and specifically for frying foods at high temperature, when you cannot live with the taste they would acquire if you used extra virgin olive oil, instead.
• The coconut miracle not ideal for frying!? -There is little doubt that virgin coconut oil belongs to the "healthy oils" - despite, or rather due to its low PUFA content. The question is: Is it also ideal for frying? If we go through our checklist, as prevoiusly said...
  
  • it contains only 1.7% PUFAs, 85.2% saturated and 6.6% monounsaturated fats, which means it's more or less PUFA free and thus not prone to heat induced oxidation
  • it's cholesterol free, so the problem with oxidized cholesterols that is rampant in fats from animal products is not a problem,
  • it's smoke point is relatively, low though, at only 163°C even the deodorized, bleeched coconut oil will form enough volatile compounds for the ugly bluish smoke to rise from your pan (Man. 1998).
  The question we have to answer is thus: Is the comparatively low smoke point reason enough to abstain from using coconut oil as a frying oil? For virgin coconut oil, the answer may be yes, for the refined, bleached, and deodorized version of coconut oil, however, the peroxide levels remains stable within the relatively narrow time window (smaller than 1h) you would use when you fry foods (see Figure 5).
  

  Figure 5: After a 30 hours of frying (not shown) the US' favorite health killer, soybean oil, has peroxide values that exceed the measuring capacity of the assay, Yuki & Ishikawa used in their 1979 study (Yuki. 1979)

  As you can see in Figure 5 this is in stark contrast to soybean oil, of which you probably know that it is heavily abused as frying oil in the US.
  
  Unfortunately, its comparatively low peroxide values don't tell you the full truth about the usefulness of coconut oil. Compared to similarly bleached and deodorized palm oil, coconut oil will have higher %FFA levels, which are indicative of an increased oxditation & hydrolysis of fatty acids and are responsible for the "soapy" flavor that made the test product in a 1998 study by Man, et al. hardly palatable. From a product quality perspective, frying with palm oil would thus be (and for most companies is) the preferable choice. From a mere health perspective, though, frying with coconut oil - especially at lower heats that do not exceed the smoke point of 163°C (vs. 229° for palm oil), is yet a good and tasty choice.
• Avocado oil, the exotic alternative - There is unfortunately little research on the long-term health effects of using avocado oil for frying.
  

  Table 2: The fatty acid composition of cold-pressed and refined avocado oil does not differ (Haiyan. 2007)

  As you can see in Table 2, avocado oil, irrespective of whether it is refined or cold-pressed ("virgin"), has a high omega-9 fatty acid content. In conjunction with the similarly oxidation resistant saturated fatty acids, it makes up roughly 84.7% of the fatty acids.
  
  

  Table 3: Comparison of selected properties, like baseline FFA and peroxide value (PV | both indicative of the presence of unwanted byproducts of storage or processing induced oxidation), antioxidant content,  persticides & co in avocado oil and olive oil (Reed. 2001)

  The risk of consuming exuberant amounts of oxidized fatty acids is thus relatively low, despite the 12.6% of fatty acids with a higher susceptibility to oxidation (note: lard contains 13.6% or more of those highly volatile fatty acids | Enig. 1983).
  
  There is no cholesterol in avocado oil, so oxidized cholesterols are not an issue. Compared to olive oil, avocado oil contains an increased amount of beneficial antioxidant, is naturally lower in peroxides and free fatty acids (this does not mean that there will be necessarily less after processing) and is usually, just as olive oil, pesticide free (Reed. 2001).
  
  Against that background it's worth taking a look at the results of a 2012 study from the University of Navarra in Spain, which found that ...

  "Avocado oil was richer than olive oil in total phytosterols at time 0 h (339.64; 228.27 mg/100 g) and at 9 h (270.44; 210.30 mg/100 g) of heating. TBARs was higher in olive oil after 3 h, reaching the maximum values in both oils at 6 h of heating treatment. Vitamin E was higher in olive oil (35.52 vs. 24.5 mg/100 g) and it disappeared earlier in avocado oil (at 4 vs. 5 h). The stability of avocado oil was similar to that of olive oil." (Berasategi. 2012 | my emphasis)

  Since no regular consumer will fry his foods for more than 3h, the previously presented evidence clearly indicates that avocado oil is an allegedly more expensive, albeit slightly superior alternative to olive oil, the last oil on our list (see below).
• Olive oil, refined or, even better, extra virgin - If it was not for the price and the taste, the whole world would probably long have switched over to olive oil as their go-to oil for everything. I am not going to (re-)cite the plethora of epidemiological evidence in favor of its beneficial health effects, here. Instead I will briefly go through our three items from the initially presented list.
  
  Olive oil has a relatively low omega-6 and virtually no omega-3 fatty acids (10.5g PUFA total per 100g). It's fatty acid profile, alone, does therefore tell us that it could be a suitable candidate for the "optimal" frying oil.
  

  Figure 6: Effect of air, light and deep-frying on p-AV of olive, corn and soybean oil (Naz. 2004). Please not that improper storage will also increase the oxidative damage to your cooking oils.

  Olive oil is cholesterol free, so the oxidation of cholesterol during the frying process is not an issue, either; and when it is heated it turns out to produce a relatively low amount of unwanted peroxidation products (see Figure 6). This would render olive oil or, as I examined previously, extra virgin olive oil (read more | see red box in particular) the perfect cooking oil, if it was not for its taste, which is not compatible with every dish you may be cooking.

References:

• Allman-Farinelli, Margaret A., et al. "A diet rich in high-oleic-acid sunflower oil favorably alters low-density lipoprotein cholesterol, triglycerides, and factor VII coagulant activity." Journal of the American Dietetic Association 105.7 (2005): 1071-1079. 
• Berasategi, Izaskun, et al. "Stability of avocado oil during heating: Comparative study to olive oil." Food Chemistry 132.1 (2012): 439-446.
• Chan, Shu-Hui, et al. "Cholesterol oxidation in whole milk powders as influenced by processing and packaging." Food chemistry 47.4 (1993): 321-328. 
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