My brother Doug is funny – the youngest of my three older brothers. He often emails me from the other side of the world with nutrition questions. He’s a world traveler/backpacker who’s been in Shenzhen, China for 8 months or so. Lately all of his friends are PUFA guzzling rice eaters (no offense of course, they’re still great people) and he’s worried about them.
He’s pretty sure that eating tons of rice ain’t good and he’s pretty sure that stir frying with peanut oil on high heat ain’t good either but he’s not entirely sure why. So, with his not legally changed but Facebook changed name he asks:
Tuesday
Dug McJones
so, what happens to all of those things [oils] when they get too hot? i mean, why does it matter that the fats get destroyed or not? and how hot is too hot? which ones are the best for cooking really hot?
i need this info as you see it, to tell to my friend who just got a huge ass bottle of peanut oil, and cooks with high heat. i told him that’s bad, but without some sort of reason why behind that statement, he doesn’t really believe it… also, next time i try to tell people why it’s so bad, if i could say more than “because my sister says so”, it would be a bit more convincing.
Yesterday
Peggy Emch
There are four groups of fatty acids in dietary fats: saturated (butter, lard, coconut oil, bacon grease), monounsaturated (olive oil, macadamia and avocado oil), polyunsaturated (omega 3s: fish and flax oils. Omega 6s: peanut, sunflower, sesame, soy, corn oils), and trans (shortening, crisco and other fats which are chemically hydrogenated).
The fatty acid molecules differ in structure. They all consist of chains of carbon atoms bonded to either carbon atoms or hydrogen atoms. The types of bonds and length vary. Saturated fats are saturated with hydrogen atoms attached to their carbon atoms. Think of a long string of carbon atoms each with a hydrogen atom attached. Monounsaturated fats have some hydrogen atoms missing and polyunsaturated fats have even more hydrogen atoms missing. Instead of the carbon atoms linking to hydrogen atoms they form a double bond between themselves. This is what makes them liquid at room temp. But this also means that the molecules are more unstable and vulnerable to damage. It’s like the hydrogen atoms protect the carbon atoms so they are stronger.
Heat, light, and oxygen all can damage the delicate polyunsaturated oils. This is called rancidity. You know how bad old peanut oil smells and you know you’re not supposed to eat it, right? That’s because it’s rancid. Well, when you cook the oils the same thing happens. They become rancid and consequently are poisonous to your body. Eating rancid oils is like eating a spoonful of oxidation. And oxidation causes inflammation. And inflammation is responsible for, well, just about everything bad that happens to a body.
So, that’s why you want to be careful when cooking with delicate oils – if you cook with them at all. BUT you also need to watch your ratio of omega 3:6. Omega 3 oils are essential – meaning that your body cannot make them all by itself. Just like vitamin C and B12 are essential – you cannot make them, you MUST eat them. Same goes for omega 3 fats. They are not present in any amount in most modern diets. Hence, most people are totally deficient in them and this is really bad because they are essential – your body needs them. You can get omega 3s from grass fed dairy and only when it’s grass fed. You can get lots of them from fish. And any wild animal meat will have them.
Omega 6 oils are kind of the opposite. They are in everything. Your body cannot make them either but you really don’t need to worry about it because of their ubiquity. And, since too much of them is inflammatory, you should watch you intake.
So, your friend (and most Asians) is not only doing himself a disservice by cooking peanut oil at high heat but by eating so much of it in any form. However, if he balances out his high omega 6 consumption with plenty of omega 3s from fish, he’ll be fine – unless it’s super excessive.
The easy way to explain all this technical shit is by remembering that pressed vegetable oils in large quantities is not found in the natural world. Hunter gatherers did not use bottles of peanut oil. They used peanuts. Any primitive people eats whole foods, and only small amounts of traditionally prepared processed foods. Hawaiians and some Asians found a way to ferment the oil out of the coconut and used that for millenia in cooking but coconut is saturated and so it keeps much longer, plus that natural fermentation process does not damage the fats in the way that high heat can.
20 hours ago
Dug McJones
wow. that’s awesome. thanks a lot for that. so the saturated fats keep the longest. right? then the monounsaturated fats. then the polyunsaturated? and by the same token, the saturated fats do better at higher heat ranges than the monounsaturated, and the mono, better than the poly. correct? (though i still cook everything at low heat) and the healthiest thing to cook with is saturated fats, regardless of the temperature. right?
and, how does extra virgin olive oil differ from regular olive oil?
17 hours ago
Peggy Emch
You got it dude! Olive oils – and all oils – can be refined to varying degrees and with various methods. Just plain olive oil is more refined, usually by using heat or chemicals to extract the oil from the olive. EVOO has been cold pressed so as not to damage the oils.
Another thing to consider s how many pressing the olives underwent. “First press” means that the olives were pressed once. Then they press them again and again to extract all of the oil. BUT when they do this you lose lots of nutrients like Vitamin E and other anti-oxidants. So first press EVOO is the best.
8 hours ago
Dug McJones
one last thing: does EVOO mean first press, or is there a “first press extra virgin olive oil”?
about an hour ago
Peggy Emch
EVOO does not mean first press. That is something additional you will find labeled on the bottle. The number of pressings will likely only be on there if it is first press. They don’t advertise for lesser pressings.
Later I found this cool article at the WellnessMama about vegetable oil processing and consumption if you’re intersted in further reading.
April 19, 2012 at 5:15 pm
I’m confused about something: Does the level of saturation actually affect the smoke point? It seems like a lot of mostly-PUFA oils (safflower, sunflower, soybean) have pretty high smoking points. Or is that because of the polyphenols and such that Mark talked about in his latest post on heating olive oil that make them more stable?
Bleh.
April 19, 2012 at 6:42 pm
Tyler, here’s what Wikipedia has to say about smoke point:
April 20, 2012 at 4:26 am
All so interesting! I learned a few things thank you
April 20, 2012 at 4:41 am
One minor quibble: Omega-6 fatty acids are essential. The problem is that they are ubiquitous, so nobody is likely to be deficient in them except, perhaps, Eskimos (who eat shed-loads of omega-3 fatty acids).
Smoke point is irrelevant. Flax-seed oil oxidises to varnish at room temperature without producing any visible smoke.
My rule of thumb: Don’t heat oils high in polyunsaturates to temperatures >100°C. See also Real-Time Monitoring of Thermally Induced Trans Fats in Corn Oil Using the FatIR™ Oil Analysis System.
Oils high in saturates & monounsaturates are stable enough for high-heat cooking.
April 20, 2012 at 7:22 am
Ooh, good catch. Essential to the body yes, necessary to worry about no.
April 20, 2012 at 4:49 am
Wow! That was a great explanation & I learned something I can now share. Thank you!
April 20, 2012 at 6:24 am
For folks wanting to find out smoke points and time taken for a fat to oxidise (and become “bad”), use the word “rancimat” in your searches.
The Rancimat Analysis is a method of establishing the oxidative stability (or otherwise) of fat.
Needless to say, animal fats come out tops, some oils from palm and coconut, particularly, up next, then down the chain until we get to industrial vegetable oils, which are very poor in comparison.
Personally, I do not like to cook at all with pressed fruit oils, like olive or avocado. These have excellent flavours of their own which work nicely sloshed over cold food.
Animal fats cook well. For me, beef dripping is tops. Ghee is very useful, which is butter with all but the fat removed through a long, slow cooking process. It is still sound in terms of oxidisation and has a high smoke point.
April 24, 2012 at 8:22 am
Grain-fed cows are usually grass-fed until the last few months of their lives, so shouldn’t they have traces of Omega-3 fats remaining in their meat? I realize that the O-3 decreases the longer a cow is grain-fed, however, no cows are grain fed their entire lives. The Omega 3 content should be on a scale from grass-fed>grain-finished>”grain fed”(grain finished for a longer time)
April 24, 2012 at 12:53 pm
Marisa, you’re right about how long cows spend in feed lots. According to beefusa.org,
Ewe gross huh? Anyway, a lot of things change in the meat of the animal fattened up on the slop that they feed cows in feedlots. Cows don’t have a whole lot of omega-3s in their flesh to begin with, compared with some other animals. Mark Sisson reviewed a study on this topic here.
June 21, 2012 at 1:12 pm
Along those lines… Grass fed cattle will provide Vitamin K2 which is vital for proper use of calcium within the body.
April 24, 2012 at 12:01 pm
Thanks for this great piece, those are all the same questions about oil that I has as well. This site is fantastic, keep up the great posts!
I hope your pregnancy is going well!
April 28, 2012 at 3:13 am
Wow, this is really helpful! I love the format (email conversation) and it made the reading even more enjoyable. I did not know that about rancidity and how it essentially meant “oxidation” but I love that line about how basically it is the cause of everything bad!
Your blog seriously kicks ass.
April 29, 2012 at 3:33 pm
Thanks Fox! Glad to hear you liked the format.
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