This is a bonus article: I usually update on Tuesdays. I’ve got something astoundingly excellent lined up for this next Tuesday, so subscribe to my RSS feed to remind yourself!
Tireless media coverage, and government-mandated nutritional labeling, has convinced everyone that trans fats are bad for us.
Fortunately, unlike most dietary scares of the past 50 years, the government and the ADA appear to have got this one mostly right: trans fats are indeed toxic. According to this data (yes, it’s a prospective study and therefore contaminated by associational confounders), consuming just 2% of your calories from trans fat doubles your risk of heart disease! They’re also associated with obesity, Alzheimer’s, and infertility in women, and they may interfere with liver function.
What’s a Trans Fat? (You can skip this if you’re not interested in chemistry)
Oleic acid, a cis-fatty acid (Source: Wikipedia)
“Hydrogenation” means that a hydrogen atom is forced into the space where a double bond once was, making it into a single bond. For instance, hydrogenating a monounsaturated fat makes a saturated fat.
Dietary fats are either saturated, monounsaturated, or polyunsaturated. “Saturated” means that there are no double bonds in the molecular structure, and no hydrogens can be added. “Monounsaturated” means one double bond, and “polyunsaturated” means…well, more than one.
The interesting part is that double bonds can be cis- or trans-…basically the chemical equivalent of right- or left-handed. It turns out that fats created (or hydrogenated) by enzymes, in mammal bodies, are all cis-handed. But chemical hydrogenation creates a mixture of cis- and trans- fats that actually favors the unnatural trans- configuration 2:1. And the resulting trans- molecules have a dramatically different shape!
Eliadic acid, the same fat in trans- form
This is why trans fats wreak havoc in your body: they’re the wrong shape, and your body simply doesn’t know what to do with them. It’s like putting brake fluid in your engine oil, or antifreeze in your gasoline.
(The alert observer will note that it is impossible to create a saturated trans fat.)
Hidden Trans Fats: They’re Everywhere
So you think “I’ll only buy products with 0g of trans fat on the nutrition label. Then I’ll be safe.” Right?
Does it contain trans fat? This won't tell you.
No.
Trans fat hides in plain sight.
Trans Fat: Hiding on the Nutrition Label
Here’s the first place it hides: on the nutrition label. If a ‘serving’ of food has 0.5 grams or less of trans fat, the label can say “0 grams”. But how many ‘servings’ are you eating? If a ‘serving’ is 50 calories, you can easily eat eight servings at a sitting—or four grams of trans fat!
How can you tell? Look on the ingredient list. If you see the words “hydrogenated” or “vegetable shortening”, you can guarantee the presence of trans fats—no matter what the nutrition label says.
Trans Fat: Hiding in ‘Heart-Healthy’ Seed Oils
Of course, we should be eating those ‘heart-healthy’ polyunsaturated seed oils instead, right? Like ‘canola’ (rapeseed) oil?
Well, aside from the fact that seed oils contain mostly pro-inflammatory n-6 (“omega-6”) polyunsaturated fats, both n-6 and n-3 polyunsaturated fats are less chemically stable than saturated fats. It turns out that the process of extracting and deodorizing them (which requires both hexane, a poisonous industrial solvent, and high heat) turns some quantity of them into…trans fats!
SEAN. O’KEEFE, SARA. GASKINS-WRIGHT, VIRGINIA. WILEY, I-CHEN. CHEN. LEVELS OF TRANS GEOMETRICAL ISOMERS OF ESSENTIAL FATTY ACIDS IN SOME UNHYDROGENATED U. S. VEGETABLE OILS. J Food Lipids Vol 1 #3 pp.165-176 Sept. 1994
Concentrations of trans isomers of 18:2w6 and 18:3w3 were measured in soybean and canola oils purchased in the U. S. […] The degree of isomerizations of 18:2w6 and 18:3w3 ranged from 0.3% to 3.3% and 6.6% to 37.1%, respectively. The trans contents were between 0.56% and 4.2% of the total fatty acids.
Vegetable oil solvent extraction plant, China.
Yes, that’s the ‘heart-healthy’ canola oil that they put in everything nowadays because it has ALA in it (the least useful omega-3). Yet the average canola oil contains over 2% trans fat! (Remember: 2% of calories = doubling of heart disease risk.) And if extraction under carefully-controlled conditions creates that much trans fat, how much more does the uncontrolled heat of cooking and frying create?
(We don’t know—but we do know that n-3 fats are less chemically stable than n-6 fats, and generally get hydrogenated first. So all those “Omega-3 Enriched!” oils become “Trans-Fat Enriched!” when you cook with them. For evidence of this, we move to the next section…)
Trans Fats: Hiding In The Deep Fryer
The third place trans fats hide is in the deep-fryer. Canola oil is the most common frying oil, because everyone knows canola is ‘heart-healthy’…right?
If you can run a city bus on it, it's not food.
Unfortunately, since polyunsaturated oils are unstable under the continuous heat of the deep fryer, canola oil is hydrogenated so it’ll last longer. (This is why we fried everything in saturated fats, like beef tallow, before the now-discredited “Lipid Hypothesis” took over American nutrition theory: saturated fats can’t hydrogenate by definition, and they don’t degrade nearly as much or as quickly under heat.)
How much?
Industrial canola oil for deep-fat frying contains 27% trans fat. (Source.)
Still want that order of French fries?
Live in freedom, live in beauty.
JS
(Did you enjoy this article? Share it with your friends! For more articles about fat, try “Why Humans Crave Fat” or “Fat and Glycemic Index: The Myth of ‘Complex Carbohydrates’“.)
Postscript: What Should I Use Instead?
Use saturated fats, which don’t hydrogenate—and monounsaturated fats, which hydrogenate to saturated fats, not trans fats. Butter, beef tallow, and coconut oil each contain only a tiny fraction of polyunsaturated fats…and if you buy grass-fed beef or butter, that fraction contains more healthy n-3 fats and less unhealthy n-6 fats.
And since a surprising number of people still believe that saturated fat is bad for you: no, it isn’t.
Patty W Siri-Tarino, Qi Sun, Frank B Hu, and Ronald M Krauss. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr Jan 2010
“A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD.”And here’s the layman’s version, from Scientific American: “Carbs Against Cardio: More Evidence that Refined Carbohydrates, not Fats, Threaten the Heart“, Scientific American, May 2010
Regarding “What Should I Use Instead,” hear, hear! I routinely save the fats from whatever meats I cook. I am a big proponent of keeping a big jar of bacon fat in the fridge to cook with, for example. Bacony goodness. Works great for sauteing veggies. Oh, and mushrooms, those wonderful little sponges that just love to soak up flavor. Put a bunch of sliced mushrooms in a pan with bacon fat and a lot of fresh minced garlic and a touch of oregano, then serve them over steak. Absolute heaven.
And to me it is the height of silliness to skim the fat from the drippings of whatever I cooked, and then replace it with butter to make gravy. Turkey gravy tastes a lot more like turkey if you use the turkey fat, for instance, and butter is expensive. The fat from the critter is free, but most people just throw it out. And, whenever I can get to my butcher, I get pork fat to render into lard for deep frying. That stuff you get in tubs in the grocery store is not real lard. I also make schmaltz, for when chickeny goodness is better.
I find it terribly sad that so many of us have been conditioned to say “Eww, fat!” The funny thing is that my relatives, although most of them believe in the low fat thing, still love to come to my house for holiday meals. As long as they don’t see how much fat I use, they don’t care. My stuff has flavor🙂
People only say “Eww, fat!” when they see it. The reaction when they eat it is always “Mmmmm, fat!”
Do you render your fat wet or dry? What is your technique?
JS
I do most of my cooking using pastured ghee in a cast-iron skillet. I’m curious what you think about what happens with the omega-3 content of the grass fed butter both in the process of converting it to ghee and in the process of using the ghee to sautee food in cast-iron.
According to this post on seasoning cast iron iron catalyzes radical polymerization of omga-3 fatty acids. She claims that the best way to season cast iron pans is using flax oil to maximize the creation of a polymerized fatty acid coating — which is the same process that happens in when the linseed oil in oil-based paint or varnish “dries”.
The question is: when cooking with ghee in the cast iron pan, to what extent would the radical polymerization happen at sauteeing temperatures, and to the extent it happens to what extent would the damaged PUFA be safely sequestered away from the food by adding it to the surface of the cast iron vs. leaving damaged fats in your food (either polymerized, trans-isomerized, oxidized)? I do notice that habitual use of ghee does lead to a consistently happy non-stick surface in that skillet!
Thanks,
Anne
Anne:
That's a very interesting post on seasoning cast iron…essentially you're making your own non-stick coating out of varnish. (My post about flaxseed/linseed oil makes the same point.)
Since ghee is mostly saturated, I suspect that cooking with it leaves your cast-iron clean because it's not polymerizing. As the seasoning article states, it's difficult to get an even varnish on the pan, and it requires controlled heat and thickness of application. Simply burning a big puddle of unsaturated fats on it (i.e. cooking at or near smoke point with high-PUFA oils) would probably mess up the finish and leave it mottled/uneven/patchy over time.
Unfortunately I've looked before for data on what sort of heat and time is required to damage PUFA, particularly n-3 PUFA, and I've been unable to find any hard data beyond what's in the article.
Recall that there are multiple mechanisms of damage: one is partial hydrogenation, which generally results in trans fats, and is what the paper I cite above is discussing. Another is oxidative damage, which results in rancidity (or 'drying' if you're using the oil as varnish), which is what 'seasoning' a skillet apparently does as per the article you linked.
Thinking out loud: oxidative damage is obviously dependent on the presence of oxygen (and aided by the presence of catalysts), which is why flaxseed/linseed oil must be stored in an airtight container. PUFA in tallow, used for cooking, is mixed in with a whole bunch of very stable saturated fats, so it's harder to oxidize than flaxseed/linseed oil, which is over 70% PUFA. Even lard, which is higher in polyunsaturates than tallow, doesn't go rancid nearly as quickly as flaxseed oil, even at room temperature. So my guess is that the PUFA in tallow is far more stable than the PUFA in seed oils…but I would love to have some real data on this.
In closing, this is a long way of saying “I don't really know, but would love to find out”. Please leave a comment if you find anything, and I'll update if I find anything. Maybe I should take up a collection to have two analyses run: one on fresh tallow, one on tallow that's been used through a bunch of deep-fryer cycles!
JS
I’d be very interested in that experiment, since I do re-use my tallow. I’ve kind of gone with the idea that, since it’s mostly saturated, my metabolism can probably handle what damage occurs from multiple uses, but it’d be nice to have something on which to base the idea (or refute it, as the case may be).
[…] always been told that canola oil is healthy, hell I’ve told patients the same thing, but as this post indicates, canola oil contains trans fats! Regardless of the quantity of trans, I am now avoiding canola and opting for canola, avocado or […]
Source?
Hitssquad:
It's impossible to make a trans fat from a monounsaturated fat by hydrogenation: I thought that was clear from the context.
I'm sure there's some way to do it chemically by desaturating it — but AFAIK that's not something that happens either during cooking or in our bodies.
JS
It was clear from the context. You were then asked for a source for that claim. You responded by repeating the claim, again without giving a source. Does simply making a claim make it true?
Let’s see what Google says:
Chris:
Here's the situation as I understand it.
It is indeed impossible to chemically hydrogenate a monounsaturated fat and turn it into a trans fat, because the only double bond becomes a single bond. Oleic acid, for instance, becomes stearic acid when hydrogenated.
However, in practice, it is possible for a half-hydrogenated intermediate to dissociate from the catalyst, at which point it may isomerize either positionally and geometrically as it returns to a stable configuration. Though I don't have access to the fulltext of your references (except the first), this is most likely what they are referring to. (Further explanation here.)
The difference here is whether we are speaking of hydrogenation, defined as the addition of two hydrogen atoms to replace a C=C bond — or the physical production of partially hydrogenated oils. In the first case, I'm correct, because that's the definition: in the second case, you're correct, because that's the physical process.
Since the second case is more relevant to the situation at hand (which I believe to be your point), I'll change the wording to reflect that.
JS
PS: I welcome your corrections, and those of all my readers: I want to keep gnolls.org as factual as I can. However, while I'm sure you mean well, it feels like you're trying to bait me into an argument instead of simply offering a correction.
For instance, you could have simply said “It is indeed possible for the physical process of hydrogenation to make trans fats from monounsaturated fats via the dissociation of intermediate reaction products from the catalyst, if the process is stopped before full hydrogenation”, and you would have saved both of us quite a bit of time.
That being said, please continue to let me know if you find anything you believe to be inaccurate.
[…] they don’t oxidize or polymerize during cooking the way that seed oilsdo, they don’t contain hidden trans fats, and they have low to zero omega-6 fat content. I discourage lard unless it’s from pastured […]
[…] always been told that canola oil is healthy, hell I’ve told patients the same thing, but as this post indicates, canola oil contains trans fats! Regardless of the quantity of trans, I am now avoiding canola and opting for olive, avocado or […]
Canola oil and soy oil, besides containing trans-fatty acids, is 85% to 90% GMO, so it is most likely contaminated with glysophate (the herbicide Round-up) which is mutagenic and even in the natural environment degrades very slowly.
Kenneth:
That's an interesting point about glyphosate. I wonder how much of it survives the refining process? It's water-soluble, so it might tend to end up in the protein and sugar fractions, rather than the fats — but I don't know for sure.
Either way, it's good to avoid consuming soy and canola products. Even if the glyphosate doesn't end up in our bodies, it damages the soil by binding mineral nutrients in addition to its other toxic effects.
JS
Is sunflower oil safe to use as frying/deep-frying oil for home use in the pan and casting it after only one use.
It's full of Omega 6 which you don't want to overload on. I use either Ghee(clarified butter) or Coconut Oil for frying.
Aenohe:
What Jen W said. Sunflower oil is a seed oil, which I don't recommend using for any reason because it's very high in omega-6 PUFA — and it's chemically extracted using the same hexane-based process as soy and canola oils, so they're likely to contain the same fraction of trans-fats seen in the article I cited.
I use only beef tallow, coconut oil, and ghee or clarified butter for frying. I use only beef tallow or coconut oil for deep-frying…and the smoke point of coconut oil is a bit low, so I only recommend that with a good thermometer or a fryer with a thermostat you can turn down to 340 degrees or so.
JS
[…] they don’t oxidize or polymerize during cooking the way that seed oilsdo, they don’t contain hidden trans fats, and they have low to zero omega-6 fat content. I discourage lard unless it’s from pastured […]
Wow! Michael Pollan was right once again. In a lecture I attended, he predicted that omega-6 would be the next “bad fat” of fad, which is rather bizarre considering that it is an essential fat.
It's not that it's not essential, it's that there's way too much of it in seed oils, which leads to an imbalanced omega 6: omega 3 ratio if one consumes a lot of seed oils.
Orhan:
Linoleic acid is indeed “essential” — but in such minute quantities (milligrams) that it's basically impossible to not get enough by eating food. Even the lowest of low-fat diets (e.g. McDougall, Ornish) get you to about 10% fat just from the intrinsic fat content of grains, beans, fruits, and veggies.
It was only discovered that it was possible to become deficient in linoleic acid once hospital patients started being fed intravenously with zero-fat diets of purified “nutrients”.
I'm not sure if you're properly representing Michael Pollan, but if so, he's wrong in this case. There is extensive research on omega-6 intake, and eicosanoid biochemistry is relatively well understood: the idea of consuming less omega-6 and more omega-3 in order to decrease systemic inflammation is a fact, not a “fad”.
JS
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[…] IS A PICTURE OF PROOF (source: http://www.gnolls.org/1240/eat-more-heart-healthy-trans-fats-we-hid-them-in-plain-sight/ […]
I’d like to point out a few things here.
First, the 2% doubling your risk for heart disease was based on your total caloric intake. That means that if you ate nothing but canola oil, which is 1-3% trans fats, your chance for heart disease would double.
The percentage of trans fats you get from canola oil is actually the percentage of trans fats in canola oil multiplied by the percentage of calories in your diet you get from canola oil.
So if Canola oil makes up 5% of the calories you get for the day, your level of trans fats would be (.05*.02)=.001=0.1%, which is considerably lower than the 2% that doubles your risk of heart disease. It’s still a factor, but it’s an order of magnitude smaller one than what you indicated.
Second, I’ve worked at two different fast-food restaurants, and the oil for the fryers in both places were carried in plastic jugs in liquid form. That means the oil is not partially-hydrogenated, because if it was it would probably be transported in solid form due to the longer shelf life of partially hydrogenated oils.
Brendan:
Yes, now that the dangers of trans fats are more well-known and labeling is legally required, many places don't deep-fry in hydrogenated oils anymore. Of course this means the oil oxidizes and goes rancid much more quickly, which isn't healthy either!
Unfortunately, most Americans get a lot more than 5% of their calories from “vegetable oils”, most of which are much higher in linoleic acid than canola. LA provides close to 10% of energy in the American diet, if I recall correctly, due to the prevalence of corn, soybean, sunflower, and safflower oils. And since that's an average, trans fats become a meaningful percentage for many.
JS
I actually expected this article to be about rumenic acid, lol…
Indirectly, I guess it was about rumenic acid:
“What Should I Use Instead?… Butter, beef tallow…”
🙂
Me:
I wrote that article, too! (About rumenic acid and the various isomers of CLA.) Link: “Trans Fat Is Good For You, But Only If It's From Meat And Butter.”
JS
Hi,
I’m curious about high oleic sunflower oil. I have been using it to make mayo.
Sandra:
That's a good question! High-oleic sunflower oil will contain less hidden trans-fat than regular sunflower oil, because it's got less linoleic acid to begin with (less than 20%, versus 50-75%).
I still don't like using processed seed oils for other reasons, including high linoleic acid content. Personally, I tend to use light olive oil for my own mayonnaise, hollandaise, etc. — and I've started mixing it with MCT oil to make it even lighter on linoleic acid and heavier on MCTs (which have their own health benefits).
Careful with the MCTs, however…too much tends to flush out the system, if you know what I mean.
JS
[…] always been told that canola oil is healthy, hell I’ve told patients the same thing, but as this post indicates, canola oil contains trans fats! Regardless of the quantity of trans, I am now avoiding canola and opting for olive, avocado or […]
MCT oil? I’m guessing Coconut oil, yes? Also, you don’t say a whole lot about olive oil, but based on the other comments I would have to assume that since it’s a seed oil then I shouldn’t fry or saute with it. Correct?
Cook with animal fats, coconut oil and palm oil. Fruit oils, like olive oil and avocado oil are best sloshed over salads and not cooked with.
It comes down to the stability of oil at heat and it should be noted that some animal fats also become unstable at high heats such as roasting in the oven. “Smoke point” is a useful ballpark figure but for a more thorough look at oxidative stability of fats, check out “Rancimat analysis”.
Gene:
Olives are fruits, not seeds, and their oil is fine in non-pathological quantities. “Light” olive oil is suitable for cooking, but not frying or sauteeing (I use coconut oil or clarified butter). Extra-virgin olive oil should not be cooked with. As Paul said, it's a matter of stability at heat.
MCT oil is made of Medium-Chain Triglycerides, and they're extracted from coconut oil. I use it occasionally when I need a fat that's liquid but completely tasteless: the problem with butter, tallow, and coconut oil is that they're solid at room temperature, and are therefore unsuitable for salad dressing or other cold dishes. And some things just don't taste right when made with olive oil…
JS
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The Jan 2010 article seemed to indicate that the ratio of saturated to polyunsaturated fats was a health issue. Does the paleo diet easily accomodate this finding?
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