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I am considering switching to beef tallow for my high heat cooking, as it has a high smoke point and is a saturated fat (which means, that it does not oxidize easily). Also recent randomized control trials suggest, that saturated fat on its own is not causally linked to heart disease problems.

From what I have learned, is that unsaturated fats, even those with high smoke points, oxidize easily, because of their chemical property of being unsaturated, which means, that they have "space" for other electrons and react easily. From the unsaturated fats, the polyunsaturated fats have twice as much potential for reaction and oxidization as the monounsaturated fats, because they have two "arms".

With beef tallow for example, it seems to be the other way around: It has a high smoke point, but even more important: It's a saturated fat and it doesn't make new bonds easily, because it has all its electrons.

Now, my question is, how are trans fats being created? Are they the product of oxidized polyunsaturated oils? Where do trans fats come from? Or are companies intentionally putting them in food for economic reasons?

I am aware, that trans fats are banned in the US, but they are not banned in EU yet.

  • " Eating foods containing saturated and trans fats causes your body to produce even more LDL, raising the level of “bad” cholesterol in your blood." - AHA – paulj Oct 15 at 11:55
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First, a little chemistry primer on what unsaturated fatty acids look like (this is petroselinic acid):

Strukturformel von Petroselinicacid
By Yikrazuul (talk) - Own work, Public domain, Link

You can see the double bond near the "middle" of the molecule. The "rest" of the molecule is attached to the same side of the double bond axis on both ends, making this a "cis" fatty acid. Rotation around double bonds requires a relatively high amount of activation energy, so this "cis" configuration is stable, at least at low-ish temperatures.

An example of a "trans" fatty acid would be elaidic acid:

Strukturformel von Elaidinsäure
By Benjah-bmm27 - Own work, Public domain, Link

Here you can see that the molecule continues on opposite sides of the double bond axis ("trans"). At higher (e.g. frying pan) temperatures, unsaturated fatty acids more readily isomerize between cis and trans, and since trans is energetically favorable, more unsaturated fatty acids will be in their trans configuration after being heated to a high temperature.

So to answer the question(s): No, trans fatty acids are not generated by oxidation, but the same conditions that favor oxidation (high temperature) also favor the generation of trans fats from cis fats. Also, the bacteria in the digestive tracts of ruminants (cattle, sheep, but also deer etc.) produce a significant proportion of trans fatty acids. In addition, the simplest (and cheapest) industrial processes to saturate ("harden") unsaturated fats produce a relatively high amount of trans fats. So yes, not adopting other processes can be economical, if this can be considered "intentional"...your call.

A more extensive explanation can also be found in the accepted answer to this question: Does preparation of food change the nutritional content with respect to fat type?

  • So smoke point has nothing to do with it? Olive oil and avocado oil have both the same potential for forming trans fats? – user1721135 Oct 15 at 13:59
  • The more unsaturated the oil "is", the more potential it has for forming trans fats (just by sheer numbers, and there seems to be a preference for polyunsaturated fatty acids to isomerize to trans). According to my research, the smoke point also does not directly relate to the propensity to oxidize, but more to the content of free fatty acids and other more volatile components. – Matthias Brandl Oct 15 at 14:08
  • So which oil is best for high heat cooking? Not avocado oil despite its high smoke point? – user1721135 Oct 15 at 14:17
  • Personally I would choose the one whose taste I think fits best with the dish, but then again I think one has to die of something in the end...but your reasoning with beef tallow containing few unsaturated fatty acids seems sound to me. – Matthias Brandl Oct 15 at 14:21

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