It’s become fairly common knowledge that olive oil and other unprocessed oils are better for you than regular vegetable oils, but most people don’t think of vegetable oil as BAD for you. Plus, vegetable oil is cheap, readily available, in practically every packaged food you can find, and extremely convenient when cooking. But if you read my Diet Dogma, you’ll know that it is one of the only things on my “NEVER EAT” list!
Lucky for me and my health, my mom switched to primarily olive oil for cooking when I was a small child, after the Mediterranean Diet became popular. As a result, I used vegetable oil sparingly as an adult, though I still used it in baking, frying, and to make certain salad dressings. I thought that the high smoke point and neutral flavor of the oil was invaluable for certain applications, because that’s what some of the cooking websites said (note: It’s really not invaluable. It’s completely replaceable and the replacements usually work better).
The Research That Changed Everything
But in my senior year of college, back when I thought I was going to go to grad school to become a dietitian, I was researching cooking oil. In one of my classes, we had talked about the American Heart Association’s endorsement of vegetable oil and about how saturated fats were terrible…but I had trouble believing that. People have used butter for a bazillion years, and we didn’t have heart disease until recently. In fact, my mom switched from margarine to butter when I was a little kid, and I recalled that both parents actually lost weight as a result.
I decided to investigate these claims myself by really delving into the research. I had already had several years of research experience, so I was quite familiar with reading research papers. As project manager of my research office, I also had paid access to a variety of medical journals through my work computer. One night, when most of my non-working college student peers were home on spring break, I stayed late at the office to dig into some vegetable oil research.
My findings were disturbing.
The best resource I found was a book by Dr. Cate Shanahan called Deep Nutrition. I was fortunate to have access to an electronic version of this book for free through my university library, but I actually purchased a copy to have on hand for reference. Dr. Shanahan is a consultant for several athletic teams and achieved wide-spread recognition for the nutrition plan she designed for the LA Lakers. She is also an experienced medical doctor, with impressive credentials. You can check out her website here.
My favorite thing about her book is that every bit of information about vegetable oil is linked to a scientific study, referenced in the back on the book. I was able to look through the studies myself, and could confirm that the information she presented was accurate and based on real, solid research. Furthermore, I examined a few studies that the American Heart Association brandishes as evidence for vegetable oil being good for you and found massive flaws with each one that I looked at.
But unless you’re a science person, you might not want to read a whole book, much less a bunch of scientific journal articles. What’s the summary? What makes vegetable oil so bad?
How Vegetable Oil Is Made
There’s nothing inherently problematic about oil, whether it’s made from plants or not. Traditionally, oil was made by from olives, coconuts, and peanuts, depending on what part of the world you’re talking about. These oils are still perfectly safe to use – in the right conditions. But modern technology now allows manufacturers to use extreme heat, pressure, bleaching agents, and chemical extraction methods to get oil out of things that our ancestors never would have been able to extract oil from. The problem with vegetable oil is that these insanely complex chemical processes damage the oil, making it unhealthy. More on that in a second.
Some oils are mechanically pressed, just like “back in the day”, but with better equipment. On the label, this is called “cold-pressed” or “expeller-pressed” oil. These oils tend to be a bit more expensive, but it’s easy to find cold-pressed olive oil – a staple in my cooking. These oils are perfectly safe to eat.
However, most vegetable oil is extracted with chemical solvents.
Here’s a breakdown of the process:
- Seeds are cleaned. The is usually a mechanical process, where they separate the hull and/or lint bits from the seeds. So far, no problems.
- Seeds are ground. They are typically ground under high heat. Some oil is harvested.
- Seeds are pressed. The pressure gets as high as 20,6850 kilopascals. More oil is harvested.
- Hexane (or another hydrocarbon) is shoved through the seed material. This chemical dissolves the remaining oil, separating it from the other organic material. Most of the hexane evaporates, where is collected and re-used.
- Remaining hexane is removed by boiling the oil and collecting the hexane that rises to the surface. At this point, the vegetable oil is fully harvested but it is not suitable for human consumption, because it’s smelly and bad tasting.
- The oil is “cleaned” with soap. Seriously. An alkaline solution of sodium hydroxide or sodium carbonate is added to the oil, where it makes soap with bits of the oil that are undesirable. The mixture is then washed and centrifuged to separate the oil from the soap.
- Oil is “degummed.” Basically, it’s either heated up or treated with an acid to remove more ickiness.
- Bleaching agents remove dark coloring and ugly bits from the oil.
- Oil is steamed with vapor between 440-485 degrees Fahrenheit. This distills it and gets rid of the bad odors.
- Oil is sold in supermarkets.
No oil that goes through this process is safe to eat.
It is damaged by the heat and pressure.
How the Fats Get Damaged
The oil manufacturing process damages the polyunsaturated fatty acids (PUFAs) that are found in most vegetables oils.
In the human body, the shape of various particles and chemicals is critical for processing – you have little goofy enzyme doohickeys floating around in your cells that specifically bind to particles that are a specific shape – it’s kind of like really complicated Legos. Because of this, shape is incredibly important when your body is digesting food. If the shape of a food particle is screwed up, you won’t be able to process it properly because it won’t fit correctly. Imagine a Lego with some of the nubs misshapen – it wouldn’t attach to other Legos very well, right?
The heat and pressure oxidize the PUFA particles, so then your body can’t grab them and process them. Instead, they sit around in your blood…eventually leading to plaque that causes clogged arteries and heart problems….not to mention spurs inflammatory processes leading to the weight gain and retention.
To make matters worse, these damaged PUFAs can damage other enzymes and things in your body. Basically, they cause what is known in science as an “oxidative cascade” where a bunch of junk gets oxidized.
That’s because oxidation is this really obnoxious process that screws up the shape of the doohickeys and gives you problems – like cancer, inflammation, weight gain (unrelated to calories in/calories out), diabetes, and other issues.
Antioxidants & Vegetable Oil
You’ve heard people say you should eat blueberries because they have antioxidants, right? That’s because lots of fruits and veggies contain compounds that help stop oxidation. In a normal, healthy body there is a certain amount of oxidation going on, but you should be getting enough antioxidants in your diet to counteract that. The amount of oxidative stress (science term defined here) caused by vegetable oil is very high, however, and many people with chronic disease have oxidative stress that far outweighs all the blueberries they could eat.
The damaged fats in vegetable oil actually tie up a lot of the antioxidants in your body, preventing them from doing their job.
Basically? You don’t want oxidized PUFAs hanging out in your body, and you REALLY don’t want them running around oxidizing other stuff.
The science is more complicated than that, of course, but that’s the gist of it. If you’re interested in that, I’d recommend reading Deep Nutrition.
Long story short…
It looks like the PUFAs, though fine (and healthy!) normally, change shape and undergo crazy amounts of oxidation when heated. After they oxidize, they also help oxidize other stuff. It’s kind of like a game of group tag, where whenever a person is tagged they become an additional tagger. Except instead of ‘tag’ it’s ‘disease-causing-oxidation’.
Essentially, the refining process heats the oils up way past their smoke points, damaging the PUFAs in the vegetable oil, and making them crazy bad for you (this link too!). Unrefined oils are another story…but unless you have lots of money, you probably can’t afford those. Plus, many of the things typically made into vegetable oil – like cottonseed – can’t be eaten WITHOUT the processing because they are naturally foul-tasting, stinky sludge (literally).
So What Do I Use?
Instead of using vegetable oils, I’d recommend using more animal fats – like butter – and high-smoke-point oils that are lower in PUFAs and higher in saturated or monounsaturated fats (coconut, avocado, olive, etc).
Just be careful – you need to use the right oil for the right job, because even healthier oils (like olive oil) can become unhealthy when heated past their smoke point. Any PUFAs in the oil will oxidize and do the same thing as vegetable oil.
Avocado Oil, peanut oil, and animal fats (lard, tallow, etc) are probably your best best for high-heat cooking, like stir-frys. You can also even fry things in refined peanut oil. Refined peanut oil isn’t great for you because it still goes through a nasty refining process, but it contains WAY less PUFAs than regular vegetable oil, so there’s not a lot that is damaged.
Basically? You can probably get away with just using olive oil, butter, and avocado oil for most applications. If you’re really into cooking, you may want to experiment with some of the other varieties.
But PLEASE, for the sake of your health…stop eating vegetable oil!
Need some help? Check out my practical guide to avoiding vegetable oil, here.