This page is YOUR resource list of all things pertaining to edible fats and oils, please bookmark if you are interested in this topic.
If there’s something YOU want to know about good fats versus bad, please post a question for me in the comments section.
No questions about your personal medical history, please. (Those are not appropriate here and will have to be deleted, sorry!)
Bad Fats: NEVER eat these!
REFINED PUFA-Rich seed OILS a.k.a. “Vegetable oil”
Canola, Corn, Cottonseed, Soy, Sunflower, Safflower, Grapeseed, Rice bran.
ALSO TOXIC: Refined Palm oil. (It’s not very high in PUFAs, but the refining is often more intense).
PLUS: Anything that says hydrogenated because it’s going to start with one of the above and process it further to generate trans fats.
Vegetable oil is an industry term that sometimes includes olive oil, peanut and coconut. However, when you see the word vegetable oil on the ingredients, it’s not going to be olive, peanut or coconut. It will be one of the cheap, refined PUFA-rich, seed oils listed above.
Good Fats: Eat THESE instead!
UNREFINED LOW-PUFA FATS and OILS
Avocado oil, Butter, Coconut Oil, Duck Fat, Ghee, Lard, Olive oil, Peanut oil, Tallow, Sesame oil, Flax seed oil, Walnut oil, Almond oil, Macadamia nut oil
Also: Anything that says cold pressed and unrefined. It must say unrefined! If it says cold pressed but is refined, it’s no good.
USE THESE FOR COOKING:
Almond oil, Avocado oil, Butter, Coconut, Duck Fat, Ghee, Lard, Macadamia nut oil, Peanut oil, Tallow
DON’T COOK THESE
Flax, Sesame, Walnut (Exception: Sesame plus peanut or other more stable oil, see below)
“Limited Use” Defined.
These oils have been refined, but because of their fatty acid profile they can handle the refining process without generating significant levels of mutated fatty acids and are therefore not going to be particularly toxic. However the refining also strips them of significant amounts of minerals and/or antioxidants so they are not as nutritious as their more expensive, higher-quality equivalents. You can think of them as the empty calories of the fat world. If you can afford to, get the better stuff. If you can’t, these are still far better than the high-PUFA oils. You’ll just need to be sure that the rest of your diet supplies plenty of antioxidants (lots of fresh greens and herbs, for example).
Everything you need to know about dietary fats and oils, summarized in one place.
WHY VEGETABLE OILS ARE TOXIC
(The short version)
The refining process damages the polyunsaturated fats, mutating the molecules into toxins with long names like 4-hydroxynonanal and 4-hydroxyhexanol, aldehydes, and others. These molecules promote free-radical reactions that damage our cellular machinery including mitochondria, enzymes, hormone receptors, and DNA.
More information on the refining below.
For everything else you need to know about these oils, please read Chapters 7 and 8 of the 2017 edition of Deep Nutrition: Why Your Genes Need Traditional Food)
IT’s NOT THE OMEGA-6
Our diets do contain too much omega-6, yes. But a common misperception is that vegetable oils are toxic because they contain omega-6, and omega-6 is pro-inflammatory. There are two points about this misperception I want to bring to your attention.
- Vegetable oils are toxic because the fats they contain are oxidized. And it’s the double bonds that make PUFAs susceptible to oxidation. But omega-3 fats have more double bonds than omega-6, generally speaking, and so seeds with a high omega-3 content, like canola, actually lead to more toxic degradation products than seeds with a high omega-6, like soy (all else being equal).
- Our brains need omega-6. Our brains are made out equal parts omega-6 and omega-3, so we need both in roughly equal amounts.
The fact that we get too much omega-6 now is a result of two major consequences of industrial food making:
- Soy is the most commonly used vegetable oil in processed foods and restaurants by a factor of nearly twice over Canola, the second most common.
- The animals we eat are fed soy and corn, which contain lots of omega-6, and the feed is often supplemented with other vegetable oils such as cottonseed that are also high in omega-6. The animals do not burn these fats for energy (neither do we), so they are stored in the adipose tissue. This means, for example, bacon from industrially produced pigs contains a lot of omega-6.
How much vegetable oil is too much?
That’s a little like asking how many cigarettes should a 4 year old smoke. More than none is too much. However because these oils are now added to spice mixes that are added to many otherwise healthy foods, it has become almost impossible to avoid entirely. Other than spice mixes, products with vegetable oil are best avoided whenever possible.
FATS v OIL
Fats are solid at room temperature and oils are liquid. Saturated fats are stiff, so highly saturated fat. (Figure below)
FATTY ACIDS v FATS
Fatty acid refers to a molecule composed of a several carbons linked together, generally anywhere from 4 to 26 carbon atoms, with a special group at the end called a carboxyl. The chain of carbon atoms may be linked together with single bonds, and be saturated, or contain one double bond, and be mono unsaturated, or contain two or more double bonds, and be polyunsaturated. Our bodies cell membranes are composed of all three types of fatty acids. We cannot make certain fatty acids, those have to come from food, these we call essential fatty acids and they come in two types: omega-3 and omega-6.
Fats Most fats and oils we eat are composed of three fatty acids bound to glycerol to form a structure called a triglyceride. Triglycerides are very large molecules and the general idea is a little like three keys dangling off a keychain. When we eat any fat or oil, our digestive system breaks down the triglyceride into free fatty acids and glycerol so that the molecules can get into our intestinal cells, then the intestinal cell reassembles them back into triglyceride and ships them out in the bloodstream as chylomicrons, a kind of lipoprotein. When we eat too much, we store the extra as fat under our skin, all in the form of triglyceride.
THE MYTH OF EXPELLER PRESSED
If my oil says expeller pressed does that mean its okay?
No. Here’s why:
Bottles of organic oil often state “expeller pressed” as a selling point, to suggest that it has been gently treated, in an extra-virgin sort of way. But that couldn’t be farther from the truth. Firstly, expeller pressed simply means that the first step of the extraction was mechanical. The second step was probably the standard, solvent extraction using hexane.
But once the expeller-pressed oil has been extracted, it’s generally also refined, bleached and deodorized. These three additional treatments guarantee that the polyunsaturated fatty acid molecules will be oxidized in ways that generate toxins like 4-hydroxyhexanal, 4-hydroxynonanol, aldehydes and more. These compounds aren’t just hard to pronounce, they’re hard for our cells to tolerate and lead to mitochondrial uncoupling, DNA damage, free radical cascades and other cell-damaging events that accelerate the aging process and contribute to disabling disease. Don’t be fooled. (For more information, please read chapters 7 and 8 of the 2017 edition of Deep Nutrition: Why Your Genes Need Traditional Food)
COOKING TIPS FOR HIGH HEAT:
The higher the heat, the more you need to be stirring unless you’re going for a specific effect, like char flavor or crispy skin.
HEALTHY OIL COMBINATIONS:
BUTTER+OLIVE: Add a pat of butter to olive oil when cooking at high heat, the saturated fat in the butter protects the olive oil and the antioxidants in the olive oil protect the protein in the butter that might otherwise burn.
SESAME+PEANUT: Add sesame to peanut oil for Asian dishes. The ratio should be roughly 4-8:1 Peanut:Sesame. Sesame is high in PUFA, but it has powerful antioxidants that, when added to low PUFA peanut oil, protect all the PUFAs.
Should I make sure to use a high smoke point oil for pan frying, wok cooking or other high-heat applications?
No. Here’s why:
Smoke point is a sciencey sounding selling point that vegetable oil salesmen use to ooze their way into busy restaurants. If you’ve read about smoke points, you’ve probably read something like this “Refined oils have higher smoke points and typically a more neutral flavor than unrefined oils, which makes them better for sautéing, frying or even deep-frying.” I think the concept of smoke point is bunk. First of all, what chef is going to literally wait for food on the stove to start smoking before stirring it? Have you ever seen that on a cooking show? Secondly, and this is the more important point, the molecular degradation that occurs in these high smoke point oils both during their manufacture and then again when they’re exposed to high heat during cooking invisibly degrades the oil, generating molecules that are dangerous to our health.
If the food you order has black char on it, you’ll probably realize someone in the kitchen wasn’t paying attention to your dish, and send it back. The higher smoke point oils enable chefs to stir less often and in so doing to overheat your food without leaving any evidence.
I’m not saying theres no such thing as smoke point. Of course there is. But the myth is that the product is somehow superior because it has a high smoke point. You can increase the smoke point of any fat by removing proteins, antioxidants, and free fatty acids. For example, ghee has a higher smoke point than butter because the clarification process reduces the protein content.
I recommend using high-quality oils and fats like butter, lard or tallow, and yes, even EVOO, for stovetop frying. But be sure to stir! It should go without saying that overcooking your dishes not a healthy practice. Who needs high smoke points? Just eat properly cooked food.
HOW IT’S MADE: EDIBLE OILS
STEP 1) EXTRACT CRUDE OIL FROM THE SEED
Manufactures produce a crude oil by extracting it in one of three ways:
- Mechanical extraction, either cold pressed (always below 120 degrees) or expeller pressed (the pressure is higher, which increases the temperature). This is the best. But it leaves a lot of oil behind in the seed or fruit, roughly half for expeller pressing, or more for cold pressing, so it’s typically done only by small batch, artisanal producers. Extra virgin olive oil is produced by mechanical extraction, as are other high-quality oils. The highest quality oils do not need to be refined and so the bottles may contain some cloudy-appearing material that’s actually very good for you. (The video below of Figone’s Olive Oil Pressing at Factory is a good example of what today’s mechanical, expeller pressing system looks like on a relatively small scale.)
- Double extraction. This is probably how most “expeller pressed” oil is actually produced. The manufacturer will mechanically press it first, obtaining about half of the oil they will ultimately be able to extract from the seed. This produces oil and an oil-rich seed cake. To remove the other half of the oil from the seed cake, they process with hexane, as below, making for a more “cost effective” product. Unfortunately, from a consumer choice standpoint, its not clear that oils produced this way won’t be called cold pressed or expeller pressed, even though that’s only part one of the process. It appears there’s simply no way to distinguish oils that have been only mechanically pressed from these “double extraction” oils, where half has been mechanically extracted and half has been processed by solvent extraction, as below.
- Solvent extraction, using hexane (also in your gasoline tank). This is the worst. They do remove as much of the hexane as they can, using bleaches or distillation, and it’s not quite as damaging to the polyunsaturated oil molecules as the refining process.
The highest quality cold pressed oils do not require any further steps and are sold unfiltered and unrefined. These are the most nutritious oils.
STEP 2) DEGUMMING
After the double extraction and solvent extraction, a sticky soapy sludge develops on top of the oil as a result of churning the phosphatides (when you work soap into a lather, your churning the phosphatides with water creating the foam). These phosphatides must be removed before refining, and so manufacturers use a “wash” of sodium hydroxide and water to accomplish this.
Cold pressed oils do not generally require degumming
STEP 3) REFINE the CRUDE OIL
Step one and, if it’s needed, step two produce what’s called a “crude oil.” Other than cold pressed oils, the crude oils all contain numerous contaminants you would not want to eat. So the manufacturer cleans it up in three more very harsh steps that damage the PUFAs: refining, bleaching and deodorizing.
Refining: This is performed to remove the free fatty acids, which would contribute to a rancid taste. This is accomplished with either an acid or bleaching agent. In the latter case, the since bleaching has been performed the process skips ahead to deodorizing.
Bleaching: This is performed to remove chlorophyll, the chemical in plants that imparts the green color. Chlorophyll must be removed from these high PUFA seed oils because it promotes rapid oxidation of the PUFA fatty acids and would lead to a very sludgy, sticky oil that wouldn’t pour out of the bottle very well. While bleaching improves its pour-ability, it also generates partially oxidized PUFAs compounds. These are the highly toxic compounds that promote oxidative stress in our bodies and can damage our DNA.
Deodorizing: This is performed to remove flavor components, which would come from chemicals originally present in the seed (such as antioxidant phytonutrients) as well as byproducts of the above steps. This is performed by heating the oil again to 510 F/ 265 c and forcing steam through it to try to capture the volatile materials.
The refined oil can be further treated to raise the melting point to create the desired, more solid texture. One method is hydrogenation, which creates a partially hydrogenated, solid fat. Another is inter-esterification, which rearrange the fatty acid locations on glycerol and also solidifies the fat. Both of these lead to generation of different forms of toxins than the above. Hydrogenation leads to the generation of fatty acids with a single trans bond, which block our body’s enzymes. Interesterification leads to the formation of triglycerides with unusual configurations and has been found to lead to elevated blood glucose levels.
WHY GOOD FATS GO BAD: THE TWO CAUSES OF RANCID TASTE
Nature does not make bad fats, factories do. By mass producing oils, we can damage them in two different ways that can lead to rancid taste.
- ENZYMES. When oils and fats are too old, they can break apart into free fatty acids, which taste bad and are one of the major causes of rancidity. Mishandling of the raw material before factory processing also promotes enzyme action. The enzymes that release free fatty acids are called lipases, and this kind of rancidity is called lipolytic rancidity. Rancid dairy is especially gross because it has a high portion of the short chain fatty acids that are powerfully bad tasting and are, in fact, partially responsible for the disgtuisting flavor and smell of vomit.
- OXIDATION. Another cause of rancidity occurs due to ultraviolet light or heat or metals and other chemicals contaminating the fat or oil. These cause oxidation reactions, and they affect the PUFA fatty acids first. The off flavor results from the fact that oxidation reactions can release free fatty acids from the triglyceride, just as enzymes can, however the freed fatty acids are also damaged chemically and can be very toxic. Rancidity resulting from oxidative release of fatty acids is called oxidative rancidity. Fish is very high in PUFA fats and both oxidative and lipolytic rancidity play a role in generating the rotten smells of old fish.
Is eating rancid food unhealthy?
Yes, in general.
If it were just enzymatic rancidity at play releasing otherwise normal fatty acids, the answer would be no. In fact, animal like vultures that seek out already killed prey seem to enjoy the released free fatty acids we find disgusting. But these animals are generally eating carcasses that are only a few days old at most and generally the parts they eat at this stage contain mostly oxidation resistant saturated fatty acids.
We don’t eat rotting meat, unless we’re living with a native Greenlander and enjoying Kiviaq (made of auks fermented in a seal skin). So when we are hungry enough to consider downing something rancid its generally going to old nuts or seeds that are high in polyunsaturated fats. Because these PUFA fats oxidize easily, if you’re getting an off flavor from nuts or seeds its unhealthy and best avoided.
BEWARE OF “NEUTRAL” FLAVOR
Some of the most toxic fats have no flavor at all, and thus we can’t rely on taste to warn us that an oil contains toxic, oxidized fats. In fact, Canola, Soy and the other RBD oils are marketed to restaurants based on their lack of flavor, meaning the chef can use the same oil regardless of the spices and other flavor profiles.
Harvard Gets It Wrong
If you care about your health, ignore Harvard and Yale–at least for now. While many leading MDs are waking up to how wrong we were to insist that saturated fat was unhealthy, these two schools are digging their heels deep in the 1950s-era dogma. Their recommendations is to avoid saturated fat as much as possible, and get roughly 25% of daily calories from polyunsaturated fat-rich foods like vegetable oils. The only evidence that supports this position is statistical (they do not offer a plausible physiologic mechanism), and their statistical work is seriously flawed by wrong assumptions and confounding variables.
In 2015, scientists at the NIH analyzed autopsy slides that were made as part of a study done in the 1970s. The study compared two diets, one rich in liquid vegetable oils (high polyunsaturated fats) and the other rich in hydrogenated vegetable oil (high in trans and saturated fats). Believe it or not, they found the folks on the hydrogenated vegetable oils had fewer heart attacks and strokes than the people on the liquid vegetable oils.
Walter Willet, the Dean of the School of Public Health, dismissed this finding as “a historical footnote.”
What Made Me Realize Harvard Gets it Wrong
I read a PhD dissertation that explained how polyunsaturated fatty acids (PUFAs) can ignite free radical reactions in our bodies. Free radical reactions are really bad. After reading more about oil processing and PUFA oxidation, I realized everything I’d learned about fats in medical school was wrong, and that it was necessary to reverse my earlier position on good fats and bad. As a practicing doctor, making this shift has not been easy, because it goes against what most of my colleagues still believe.
This section defines some common scientific terms for those interested in more of the chemistry.
BEST METHOD OF DETERMINING OXIDATIVE STABILITY: Activated Oxygen Method or AOM, I think it’s heating to 100C with peroxide, and the longer it takes to get to a certain point, the more it resists oxidation.
RANCIDITY=any off flavor. Two reasons: free fatty acids released from trigylceride, producing an off flavor. And Partial oxidation of the fatty acids.
FREE FATTY ACID FLAVOR (from vegetable oil manual I downloaded):
The liberated free fatty acids have a distinct flavor and odor which are more disagreeable when the fatty acid chain length is shorter than 14 carbons
OXIDIZED FATTY ACID FLAVOR (From veg oil manual)
Hydroperoxides themselves have no flavor or odor but break down rapidly to form aldehydes, many of which have a strong, disagreeable flavor and odor.
“Hydrolytic rancidity, also called hydrolysis or enzymatic oxidation, occurs in the absence of air, but with moisture present. This normally is accomplished through enzymatic peroxidation, where enzymes found naturally in plant oils (i.e., lipoxygenase, cyclooxygenase) and animal fats (i.e., lipase) can catalyze reactions between water and oil.
Another degradation process is microbial rancidity, in which micro-organisms such as bacteria, molds and yeast use their enzymes to break down chemical structures in the oil, producing unwanted odors and flavors. Water needs to be present for microbial growth to occur.”
OXIDATION: Double bonds in the fatty acid reacting with oxygen.
OXIDIZED: Double bonds in the fatty acid that have reacted with oxygen to generate reaction products, usually with toxic e
IODINE VALUE: How many double bonds are present on average in the triglycerides in the oil. Does not distinguish between mono and poly. Higher value represents more double bonds.
PEROXIDE VALUE: Peroxide determination is the most widely accepted method for oil flavor quality determination. Peroxides are the major initial products of lipid oxidation and are measured by techniques based on their ability to liberate iodine from potassium iodide or to oxidize ferrous to ferric iron. Their content usually is expressed as milliequivalents of oxygen per kilogram of fat. Peroxide values of 0.5 meq/kg or less generally are necessary for a high flavor score. Because of the transitory nature or instability of peroxides, the level of peroxides may not serve as a true indicator of the actual state of oxidative rancidity of the fat or oil. During the course of oxidation, peroxide values reach a peak, then decline
Interesterification leads to elevated glucose: https://dx.doi.org/10.1186%2F1743-7075-4-3
Refining Steps: http://canola.okstate.edu/canola-info/canolaoilmeal/oilprocessing.pdf