Nutrition Science Marissa Olsen Nutrition Science Marissa Olsen

​​Seed Oils: The Underlying Cause of Obesity and Disease 

Seed oil started out as industrial machinery lubricant, and now the government is telling us it’s the healthiest food for the human body.

There is a hidden ingredient in our food that is causing obesity and common chronic diseases like diabetes and heart disease.

Although bacon cheeseburgers, carbohydrates, and sugar have traditionally been blamed for rampant obesity and metabolic disease, they are not actually the root cause. The hidden ingredient in our food—especially in almost all restaurant and processed food—doing the real damage to the human body is vegetable oil, more accurately called “seed oils.”

Seed oils are known scientifically under many names: linoleic acid, omega-6 fatty acids, and polyunsaturated fatty acids (PUFAs). Dr. Cate Shanahan, long-time nutritionist for the LA Lakers and author of Deep Nutrition, calls these oils the “Hateful Eight”—including soybean, corn, canola (rapeseed), safflower, sunflower, cottonseed, grapeseed, and rice bran oil.

None of these seed oils were historically part of the human diet. Our ancestors didn’t press oil out of soybeans or corn in the wild—in fact, humans didn’t eat grains or beans at all until relatively recently. Historically, our ancestors were hunter-gatherers who ate mostly meat and fruit. They primarily hunted large game (ruminant animals) and gathered eggs and ripe fruit. The traditional human fat sources included animal fat as well as fat from fruits like olives, avocados, and coconuts.

There are three basic types of fat: saturated, monounsaturated, and polyunsaturated. Saturated fat comes mostly from animal fats and coconut oil. Monounsaturated fats are found in fatty fruits like avocado and olive. Polyunsaturated fats are primarily found in seeds.

The 3 main kinds of dietary fat.

Saturated fat is solid at room temperature (think beef tallow and butter) because it is fully “saturated” with hydrogen, meaning it has no double bonds—so it resists bonding with oxygen and oxidizing. This allows the fat molecules to stack neatly, making them stable and solid. In contrast, mono- and polyunsaturated fats have one or more double bonds, creating “bends” in the chain that prevent them from stacking and make them liquid at room temperature.

If a fat is not fully saturated with hydrogen, oxygen can attach to those double bonds. Monounsaturated fats (with one bend) and polyunsaturated fats (with many) are therefore prone to oxidation. Oxidized fats go rancid and contribute to inflammation and disease in the human body.

The fats we eat get incorporated into our tissues. Every cell in the body has a phospholipid membrane—meaning the cell’s outer wall is made of fat. When those membranes are built from unstable polyunsaturated and monounsaturated fats, they become weak and prone to damage. This can lead to metabolic disease, including diabetes, obesity, heart disease, stroke, and cancer.

graph from optimisingnutrition.com

About a century ago, polyunsaturated fats were introduced into the food supply. It started with Crisco, a company that chemically processed cottonseed oil to market it as a “heart healthy” alternative to tallow, lard, and butter. Prior to WWI, cottonseed oil had been used to lubricate machinery. After the war, the surplus was sold to Americans as food.

Not only were seed oils introduced into human food, but they were also used in animal feed. Monogastric animals (like chickens and pigs) store the fats they eat without converting them. So, when they’re fed seed oils, we consume those stored PUFAs when we eat chicken skin or bacon.

Cows, on the other hand, are polygastric (with four stomachs) and have gut bacteria that convert even corn and seed oils into saturated fat. So, corn-fed beef still produces saturated fat–rich tallow and butter. This makes ruminant fat (from cows, lamb, bison, etc.) the safest and most stable fat for humans. In the carnivore community, we say: “Cows are king.”

Even grass-fed cows contain a small amount of PUFA—red meat has ~3% PUFA in grass-fed and ~6% in corn-fed beef, or about 3 grams in a pound of 70% lean beef. Eggs also contain around 0.5g PUFA each unless the hens are corn- and soy-free. Since red meat and eggs are some of the best foods for humans, a small amount of PUFA is unavoidable—but the goal is to keep it under 10g/day.

Unfortunately, there is rampant misinformation in the U.S. about seed oils. Many doctors and nutritionists recommend high PUFA intake based on the idea that it lowers LDL cholesterol, which they associate with heart disease. But newer, more accurate studies show that lowering cholesterol does not prevent heart disease—and can even increase the risk.

Some researchers suggest that what matters is the ratio of omega-6 (PUFA) to omega-3 fats. But this is misleading. While omega-3s (like in fish oil) are technically PUFAs too, they’re not as harmful and may have some benefits. But focusing on the ratio is a distraction. The total amount of omega-6 fats is what matters most—and that number needs to be as low as possible. These fats are toxic, bioaccumulative, and extremely slow to detox.

The half-life of linoleic acid (the primary omega-6 in seed oils) is 680 days—meaning it takes nearly two years to clear just half of what’s stored in your body. It takes 4–7 years to fully detox from decades of seed oil consumption. Since this toxin is linked to obesity, diabetes, cancer, and other diseases, we need to avoid it like the plague.

So, how do we do that?

At home, it’s simple. Throw out all vegetable oils (they’re all seed oils), and use only beef tallow, butter, coconut oil, and high-quality olive oil. Avoid the fat from chicken and pork, but you can still enjoy the protein from boneless, skinless chicken breasts, fat-free ham, or lean pork loin.

Avoid all seeds, beans, grains, and nuts—they’re packed with seed oil and other plant defense chemicals.

The harder part is restaurants. Studies show up to 40% of the calories in a typical restaurant meal come from seed oils. Everything fried, sautéed, or dressed in sauce is usually cooked in them. French fries, ranch dressing, stir-fries, sautéed onions, chicken wings—it’s all seed oil.

However, a few restaurants use beef tallow fryers (e.g., some Buffalo Wild Wings locations) or butter-based cooking. Your safest bets are steak and burgers (no bun or mayo), since those are usually grilled without added oil. Ask for butter packets or bring your own. For salads, ask for oil and vinegar and add your own dressing. Call restaurants in advance when they’re slow and kindly ask about their cooking fats.

Even some “butters” in restaurants are 50% seed oil blends. Fast food burgers, surprisingly, are often 100% beef and free from seed oils—just add tomato, pickles, onions, and mustard if you like.

In France and Italy, traditional cuisine avoids seed oils. This is part of the “French paradox”—they eat lots of fat and carbs but don’t get fat or sick like Americans. Authentic European restaurants are more likely to use real butter and animal fats, but in the U.S., always confirm.

What happens when you stop eating seed oils?

After removing seed oils and keeping PUFA intake below 10g/day, I noticed rapid improvements. Within three months, I could eat moderate carbs without gaining weight or triggering intense cravings. I felt stable and normal again—like when I was a kid.

Another benefit? No more sunburn. Many people in the carnivore and pro-metabolic communities report that eliminating seed oils makes them more resistant to sun damage*. This makes sense—our ancestors lived near the equator and were exposed to lots of sun without sunscreen or clothing. It’s not the sun causing sunburns; it’s the unstable oils in our tissues and the chemical sunscreens damaging our skin.

What should you eat instead?

The best way to heal is to eat what our ancestors ate: meat, fruit, and eggs. Fruits (technically the sweet part of the plant that holds seeds) include not just apples and oranges, but also avocado, olives, cucumbers, squash, and coconuts. Some people also tolerate cooked root vegetables like carrots and sweet potatoes. Meat and fruit don’t contain plant toxins or seed oils—and they’re what our bodies are designed to thrive on.

Beans, grains, and nuts? These are seeds, and they’re full of both PUFAs and plant toxins (gluten, lectins, oxalates, phytates, saponins, etc.). Humans aren’t designed to digest seeds—and our ancestors rarely ate them unless they were fermented or sprouted to reduce toxicity.

Even olive oil and avocado oil, while monounsaturated and lower in PUFA, are prone to oxidation if not cold-pressed and stored in dark bottles. Plus, studies show 80% of these oils on the U.S. market are adulterated with seed oils*. Thankfully, Costco’s Kirkland Signature olive oil and Chosen Foods avocado oil are among the few verified pure brands.

The food industry is not protecting you. From replacing tallow with canola in the ‘80s to allowing mislabeled oils today, there is massive fraud and corruption. But you can take back control of your health.

Start today. Throw out your seed oils. Choose beef, butter, eggs, and fruit. Bring your own butter to restaurants. Call ahead and ask about ingredients. Support restaurants that use real fats. Share this knowledge.

The benefits? You’ll lose weight, burn fat, stop sunburning, reduce cravings, and heal long-standing health issues. You’ll feel stable, energized, and in control again.

Even if you cheat and eat junk food—never eat seed oils. Just remember: it takes 680 days to clear out half.

Within 3 months of reducing PUFA to under 10g/day, I started healing and losing weight. You can too.

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