CHAPTER 9:
SEED OILS
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“I suffered my very last migraine right before I went on the Whole30 program. This change is totally amazing for me, because I’ve been getting migraines three to four times a year, for a week or more at a time, for the past eight years. I would be totally incapacitated—unable to do anything except just lie there in pain. Now I feel fairly confident that I can look forward to a migraine-free future. Thanks, Whole30, for changing my life!”
—Laura R.
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Industrial seed oils or vegetable oils are extracted from the seeds of various plants. While these oils come from a variety of sources (peanuts, soybeans, sunflower seeds), they all share two common denominators—a high proportion of polyunsaturated fat (PUFA) and a large amount of omega-6 fatty acids. Diets high in these types of fats—specifically when derived from seed oils— have been shown to directly promote systemic inflammation, thereby violating our fourth Good Food standard.
Can we just leave it at that? Be our guest and skip the rest of the chapter if you’ll take our word for it. If you’d like the background, read on.
PUFA OVERLOAD
Polyunsaturated fats (PUFA) are one of three general categories of fats. There are many different types of PUFAs, but we’re going to focus on omega-6 and omega-3 fatty acids. These are both considered essential fatty acids, necessary for human health but unable to be manufactured in the body—which means that the only source of these fats is our food.
AN OMEGA-3, OMEGA-6 PRIMER
Omega-3 fatty acids have important structural and metabolic functions in the brain, influencing memory and performance, and are important for retinal health. Two types of omega-3, EPA and DHA, have also been shown to reduce inflammation and may help lower risk of chronic health conditions, such as heart disease, cancer, and arthritis. Omega-6 fatty acids are also critical for healthy brain function, metabolism, growth, and development—but if we eat too many, they can promote inflammation in the body.
We need some PUFA in our diet to be healthy—but too much causes problems, especially if it’s too much omega-6. The trouble is, seed oils contain a lot of omega-6, and a modern diet includes a lot of seed oils, because seed oils are in everything.
Almost every restaurant cooks with them, whether they’re fast-food joints, chain restaurants or fine-dining establishments. They’re found in most processed foods as well—everything from tortilla chips to soups, salad dressings to fruit snacks. The estimated consumption of soybean oil alone in the United States increased more than a thousandfold (!) between 1909 and 1999; the National Institutes of Health estimates that soybeans, usually in the form of oil, now account for an astonishing 10 percent of total calories in the United States.
Ten percent of total calories is a lot.
These seed oils are ubiquitous because they’re cheap—but they are not healthy.
Scientists believe our growing PUFA intake from industrial seed oils has played a significant role in the increase of inflammation-related conditions like obesity, insulin resistance, type 2 diabetes, and cancer over the past few decades. And it’s quite likely that most of the diseases of modern civilization * are linked to the radical shift in the composition of fats in our foods.
FIRST VIOLATION: OXIDATION ON THE OUTSIDE
The first concern with PUFAs in seed oils has to do with their stability when exposed to external stressors like air, light, and heat. Exposure to these stressors can cause molecules in these oils to react with oxygen in the air and form free radicals, a process called oxidation, or “going rancid.”
FREE RADICALS
Free radicals are naturally occurring, highly reactive molecules that play an essential role in many biological functions, like immunity and cellular repair. Having some in the body is good, but having too many is not. Balance is critical, because an excess of free radicals can damage cells (and your DNA). An overabundance of free radicals has been implicated in Alzheimer’s disease, high blood pressure, and even cancer … and has a severe inflammatory effect in the body.
Mother Nature gave all oily seeds a built-in defense mechanism to protect their fats from oxidation. These compounds (appropriately termed antioxidants) inhibit the oxidation process, delaying rancidity.* We want our dietary oils to contain these healthy antioxidants—but seed oils contain few (if any).
Industrially-produced seed oils have been refined, bleached, and deodorized—usually using nasty chemical solvents—to remove their natural flavor and aroma, making them easy to blend undetected into any food product. The trouble is, the refinement process also removes a large percentage of the health-promoting antioxidants. (Some manufacturers try to combat this by adding artificial antioxidants back into their seed oils, but numerous studies have shown that supplemented antioxidants don’t work in the same protective fashion as naturally occurring antioxidants.)
Even before processing, PUFAs are the least stable kind of fat, but with their natural antioxidants largely removed, seed oils are even more vulnerable to rancidity.
OILS GONE BAD
These PUFA-rich seed oils are so vulnerable that even at room temperature and in indirect light (like the kind you find in the grocery store), oxidation occurs inside the bottle—especially as these oils are often packaged in clear plastic. That means the seed oil in your cart may be partly rancid before you even bring it home from the store!
We then cook with these seed oils, exposing them to yet more air, heat, and light. During the cooking process, the antioxidants that survived the refining process “sacrifice” themselves in a futile effort to prevent further oxidation. Once oxidation starts, it’s hard to stop—“auto-oxidation” occurs at an increasing rate, like a free radical chain reaction.
Does eating rancid oils sound like a terrible idea to you too?
Studies show that some of these oxidized fats are transformed into toxic substances that can create damage in the liver, which means ingesting oxidized PUFAs puts your health at risk.
But that’s just strike one.
SECOND VIOLATION: OXIDATION ON THE INSIDE
One of fat’s jobs is to help build and maintain our cell membranes. This means that the type of fat we eat is reflected in the makeup of our cell walls. If we eat too many PUFAs, some will probably have oxidized in the bottle (and our frying pan), leading to toxic byproducts when ingested. The rest—which hasn’t oxidized—is then built into our cell walls. But just as seed oils are the least stable on the shelf and in the frying pan, they are also the least stable in the body.
Polyunsaturated fat is the most likely type of fat to oxidize inside our bodies.
When we eat too much PUFA-rich seed oil, it makes up a larger and larger proportion of our cell membranes, which in turn makes our cells themselves more vulnerable. (It’s like building a house with termite-ridden wood. The more termite-damaged wood you use, the more unstable the house.) The PUFAs in our cell walls can be oxidized by free radicals, creating toxic byproducts and setting off a cascade of equally destructive chain reactions. These reactions cause all sorts of damage, and provoke (you guessed it!) systemic inflammation.
Strike two.
THIRD VIOLATION: TOO MUCH OMEGA-6
Remember when we said seed oils are in everything, and so we eat a lot of them? It’s not just about the amount of PUFA we consume—it’s also about how much of that PUFA comes from omega-6 fatty acids. Seed oils contain an abundance of omega-6, while providing us with virtually no omega-3s. While some omega-6 fatty acid in our diet is essential for good health, too much throws our body’s fatty acids out of balance. And if the amount of omega-6 in our bodies is disproportionately high compared with the amount of omega-3, that spells trouble—specifically, more pro-inflammatory compounds in the body, and less anti-inflammatory activity. Which is the long way of saying:
Consuming seed oils with high levels of omega-6 promotes systemic inflammation.
Strike three, they’re out. For these three reasons, industrially-processed seed oils violate our fourth Good Food standard.
HIGH-OLEIC OILS
Manufacturers are catching on to the whole omega-6 problem and are starting to modify safflower and sunflower seeds into “high oleic” versions rich in oleic acid, a form of monounsaturated fat. These modified seed oils have fat profiles similar to that of olive oil, which we say is a very healthy choice, and may be confusing to consumers trying to make smart oil choices. Don’t be fooled. Unlike extra-virgin olive oil (which is always pressed without the use of high heat, solvents or extraction chemicals), most of these high-oleic oils are still highly refined—processed using unhealthy chemicals and heat. In addition, you can’t always trust these new forms of “cold pressed” oils, as the use of the phrase is often nothing more than a marketing technique. The smartest choice is to avoid all seed oils and rely on the stable, health-promoting oils we’ll outline in Chapter 15 for cooking, sauces, and dressings.
Common seed oils and vegetable oils to avoid
canola (rapeseed) palm kernel
chia peanut
corn rice bran
cottonseed safflower
flax (linseed) sesame
grapeseed soybean
hemp sunflower
Even though seed oils violate only one of our four Good Food standards, that’s a good enough reason for you to clean out your cupboard and throw them all away. Besides, with all the healthy alternatives we’re going to give you in the next section, there’s not going to be room for them—in your diet or in your pantry.