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Over the years, eggs have been vilified, then given a reprieve with regard to cholesterol, but when reading Srinivasan & Rose (2014), there is mention of lipid oxidation which can supposedly cause heart disease.

During the cooking process, the fat in eggs can be oxidized through a process called lipid oxidation, which can cause serious health problems including heart disease and can destroy essential fatty acids and vitamins in eggs

[...]

The results supported the hypothesis and showed that heat oxidizes the fat in eggs. We found that the amount of fat in an egg is inversely proportional to the amount of heat applied to it. This information can raise awareness of harmful health consequences of consuming eggs exposed to high temperatures during cooking and encourage consumers to cook eggs using methods that do not require the egg to be heated to very high temperatures.

Maybe I am confused, as fat is fat (oxidised or not) and being that they found that the amount of fat in an egg is "inversely proportional to the amount of heat applied to it" that indicates less fat after cooking at high heat compared to low heat.

Total fat content and heart disease risks aside, does cooking eggs at high temperatures oxidise more fats than low temperatures?

References

Srinivasan, A. & Rose, B. (2014). The Effect of Cooking Method on the Amount of Fat in an Egg. Journal of Emerging Investigators https://emerginginvestigators.org/articles/the-effect-of-cooking-method-on-the-amount-of-fat-in-an-egg

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    "The Journal of Emerging Investigators is a science journal and mentorship program publishing research by middle and high school scientists." "We accept submissions on a rolling basis. This means that as manuscripts are accepted for publication they will be immediately formatted by the editors and published online." "JEI Learning Center offers a prestigious, financially rewarding, and personally fulfilling franchise opportunity."
    – philipxy
    Commented Dec 12, 2022 at 5:12
  • There is a fairly fundamental problem with identifying temperature as a variable in cooking eggs. Boiling an egg (at least if you do it at sea level) has a constant temperature. The only way to vary temperature is to use a different cooking method entirely, like frying. but cooking methods vary in many factors other than temperature, so you can't assign the differences to temperature.
    – matt_black
    Commented Dec 15, 2022 at 12:25

1 Answer 1

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The "confusion" is caused by the bad wording of the abstract.

Page 2 more properly says:

The amount of fat extracted from the egg yolks was inversely proportional to the amount of heat applied.

The solvent removed non-oxidized fat, and since "fat is fat", that means that this is also a measure of the amount of oxidized fat.

So the experiment (which itself has a few problems) led to the conclusion that higher temperatures oxidize more of the fat.

That isn't an unexpected conclusion, so there is no obvious need to be skeptical about it.


On the other hand, the experiment itself isn't very good, and the conclusion as stated is unwarranted.

The different results were caused by the temperatures that the yolks experienced, not by the cooking temperatures. I suspect that the boiled eggs were very hard boiled with very solid yolks, and that the fried eggs were cooked more gently and cooled more quickly, and so ended up with softer yolks.

(And consider that frying fat is normally a higher temperature than boiling water, not lower, which contradicts their thesis about "cooking temperatures".)

Even worse, the experimenters filled their report with interjections about heart-disease. If this were a proper experiment, that aspect would be totally omitted as being irrelevant, or it would be mentioned as "of possible significance" in one small section at the end.

A much better experiment would have been to vary only one factor. For instance, compare eggs that have been boiled for different lengths of time, allowing their yolks to come to different temperatures.

Or better yet, work with only yolks, gradually raise their temperature, and take test samples throughout the process. And then repeat the experiment at faster and slower heating rates to account for possible effects of cooking time.

The authors don't seem to be able to stick to one simple factor at a time, nor do they stick to one simply concept at a time (e.g. the editorializing about heart-disease).

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  • So the takeaway with this is that soft yolks have little to no oxidised fats, and hard yolks have much more? Commented Dec 12, 2022 at 3:05
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    @ChrisRogers, that would be my conclusion based on their not very rigorous experiment. (As for whether oxidized fats are bad for the heart, that's a completely different question.) Commented Dec 12, 2022 at 3:19
  • After re-reading the abstract I would conclude the same as they were trying to test "the hypothesis that hard-boiled eggs will contain the least amount of extracted fat (indicating the most oxidized fat) compared to raw and fried eggs." Commented Dec 12, 2022 at 3:28
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    @ChrisRogers, but I suspect that comparing a soft-boiled egg against a hard-fried egg would produce the opposite result. Their experiment has many variables (bad design), and they unjustifiably chose to attribute the different results to only one of them (bad science). Commented Dec 12, 2022 at 4:32
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    Probably worth mentioning that the most likely reason the authors didn't produce a professional academic paper is because they were attending Pittsburgh Science and Technology Academy at the time, which has enrolments for Grade 6-12.
    – Oddthinking
    Commented Dec 12, 2022 at 14:06

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