Are Vegetable and Seed Oils Bad for You?


Fats are good for you: if you pay any attention to the keto and low-carb dieting world, you’ll know that this is a pretty reliable rule of thumb. Keto authorities and diet gurus speak lovingly of butter and bacon fat and marbled ribeye steaks, fat sources that for decades we had been warned against. As for fats that are generally recognized by everyone as very healthy –olive oil, avocados, rich nuts, seafood packed with Omega-3’s – they get no less love in the keto community.

But there’s one grand exception to this general guideline: keto dieters are taught to avoid vegetable oils, especially industrial seed oils, like the plague. You may have seen advocates say things like “these oils are making you sick” and even “vegetable oils are killing you.”

Vegetable oils are just fats – they have no carbs, and they prompt no immediate blood sugar or insulin surge, issues of particular importance both to keto dieters and people with diabetes. And many mainstream health authorities, such as the American Heart Association, tout veggie oils as healthy options. So, what’s the big deal?


Defining Industrial Seed Oil

“Vegetable oil” is a broad category, too broad for our purposes – any oil extracted from a plant can be technically considered a vegetable oil, from corn oil to cocoa butter.

What we’re really talking about are vegetable oils that are extracted from seeds using modern processes on an industrial scale. For the most part, that’s soybean, canola, and corn oil: those three alone make up some 75% of the added fats market, and constitute an enormous percentage of America’s calorie intake. Some other less common oils, such as safflower and cottonseed oil, fall into the same category.


The Rise of “Salad and Cooking Oils”

Mistrust of vegetable oils starts with a simple correlation: over the past several decades, as diabetes and obesity have spiraled out of control, we’ve been eating more and more of these oils. Take a look at this chart from the Pew Research Center:

Modern American Diet Over Time - PEW RESEARCH

Americans are eating more than ever, and the gain is almost entirely concentrated in two food groups: grains and fats. That grains have contributed to the obesity epidemic will be no surprise to most ASweetLife readers. The contribution of fats might be a little bit more intriguing. The entirety of that increase was concentrated in the “salad and cooking oils” category. According to the USDA, in 1970 there were about 15 pounds of salad and cooking oils bought and consumed for every consumer; by 2010 that number had increased to over 50 pounds, and is only expected to keep increasing. Meanwhile, the use of all other cooking fats under consideration – butter, lard, shortening and so on – actually declined by about 10 pounds per year, or 33%.

The massive increase in salad and cooking oil consumption is probably the single most dramatic dietary change for Americans since the dawn of the obesity epidemic. (While a small percentage of this increase represents the increasing popularity of olive oil, the rise is almost entirely the doing of the usual suspects, soybean, canola, corn and friends.) Levels of meat, vegetable, dairy, fruit and even sugar consumption have stayed mostly steady, with some changes within categories (eg more chicken, less beef; more cheese, less milk). Correlation is not causation, and therefore this is no smoking gun, but it’s been enough to provoke widespread mistrust of this particular nutritional change.

Putting the Industry in Industrial

There is also a deep skepticism regarding the history and manner of seed oil production. These oils are largely extracted using advanced processes and many chemicals, all to produce an ingredient that our more metabolically-healthy ancestors would never have recognized.

Consider, if you will, canola oil. Canola oil is extracted from a variety of the rapeseed plant, an unfortunately-named relative of nutritional superstars like broccoli and mustard. So far, so good, right?

Rapeseed oil has been cultivated almost from time immemorial, but for its first several thousand years, it wasn’t very popular as a food. The rapeseed is naturally very high in erucic acid, a substance that is toxic in large doses and gives the oil a distinct flavor that must have never caught on. It found its greatest popularity after the invention of the steam engine, when it was found to be a superb engine lubricant.

In the 60’s Canadian scientists began to breed rapeseeds to reduce the toxin levels and emphasize other desirable characteristics. By 1978 they had hit on a winning genetic combination, and trademarked the name “Canola.” It was not sold in the US until 1985, when the FDA declared that it could be classified as a Generally Recognized as Safe. Soon thereafter its popularity skyrocketed, and it won many awards from health and nutrition societies. Pesticide-resistant GMO varieties soon followed, and now dominate the market.

How is canola oil made? The seeds are cooked, flaked, then cooked again. Some oil may be extracted the traditional way, with a press, but the rest is harvested through the use of a solvent named Hexane, a byproduct of crude oil production. More refining steps follow: the crude canola oil is subjected to multiple additional processes to result in a clean, colorless, odor-free and shelf-stable product.

These oils are modern marvels of science, but all this processing and refining raises suspicions. Are we really supposed to eat something like this, that our ancestors never did? A 2018 study found that “the refining processes destroy its nutritional values.”

Canola oil also has many industrial applications: the Manitoba Canola Growers proudly boast of non-edible uses such as “softening agent for applying plastic casings on window panes” and “mold releaser in metal fabrication.”

Omega 6:3 Ratio

You’ve probably heard that Omega-3 fatty acids are very good for you. Less well-known are Omega-6 fatty acids, which are … complicated. Omega-6 fatty acids aren’t necessarily unhealthy, and many healthy whole foods contain good amounts of them, including eggs, nuts, and seeds. Too much, though, looks like a bad idea.

Many experts have focused on the ratio of Omega-6 to Omega-3 fatty acids in our diet as a convenient way to analyze the healthiness of our fat intake. Anthropological estimates suggest that for most of our long evolutionary history, humans consumed a ratio of Omega-6 to Omega-3 of about 1:1. Today, that ratio is badly out of whack: a 2002 study found that it had grown to at least 16:1.

Our Omega-6 consumption is so out of whack largely because of the huge amount of industrial seed oils in our diet. Corn oil is the most flagrant offender here: its ratio is something like 50:1. Soybean, cottonseed, palm and many other oils also tip the scales at 15:1 or worse. (Canola oil is actually an exception, with a ratio of 2:1). Animal fat sources, which used to make up a much larger percentage of America’s fat consumption, tend to have Omega-6 to Omega-3 ratios of close to 2:1.

Many theorize that this imbalance has grave health consequences. Researchers have argued that the excess of Omega-6 fatty acids “promotes the pathogenesis of many diseases, including cardiovascular disease, cancer, osteoporosis, and inflammatory and autoimmune diseases” and that that inflammation caused by these acids contribute to “numerous chronic diseases such as rheumatoid arthritis, atherosclerosis, dyslipidaemia, diabetes, obesity and heart failure.”


Insulin Resistance

Most of those bad health outcomes are still subject of study and debate, and we cannot declare definitively that industrial seed oils are linked with these diseases. But one of the strongest links, and one of particular interest to readers with diabetes, appears to be between seed oils, obesity, and insulin resistance.

Some of this data comes from animal studies. For instance, a high corn oil diet induced insulin resistance in mice (and made them measurably lazier too!), and that a diet high in soybean oil “is more detrimental to metabolic health than a diet high in fructose or coconut oil.” It’s not just mice, of course: even maternal Omega-6 intake is associated with excessive infant weight gain.

This 2016 review summarizes for us: “A high omega-6 fatty acid intake and a high omega-6/omega-3 ratio are associated with weight gain in both animal and human studies… High omega-6 fatty acids increase leptin resistance and insulin resistance… A balanced omega-6/omega-3 ratio 1–2/1 is one of the most important dietary factors in the prevention of obesity.”


Industrial Seed Oils are Hiding Everywhere

It doesn’t take too much effort to go to your pantry and toss out any canola, corn or soybean oil you find, and replace them with avocado, coconut or olive oils. And it’s not too tough to stay away from fried foods. Those are good first steps, but unfortunately they don’t address the truly insidious nature of veggie oil in our modern society. The reason consumption has skyrocketed is not so much that we’ve been cooking with more industrial seed oils, but rather that so much has been injected into our foods without our realizing it. Vegetable oil is almost omnipresent in packaged and processed foods, and not just in obvious places like salad dressings or frozen hash browns – grab the nearest box of crackers or granola bars and you’ll see.

Although the science of industrial seed oils is largely unsettled, there is very little debate that processed and highly processed foods, the foods that are hiding massive amounts of industrial seed oils, are best avoided. The good news is that if you’re following a low-carb or ketogenic diet, you’re likely already emphasizing vegetables and protein and healthy fats, and cooking with raw ingredients.

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