Why Seed Oils Are Bad: What You Need to Know

Written By Jason Merrill

Update: A peer-reviewed research study from Weill Cornell Medicine, published March 14, 2015 in Science, has linked an ingredient found in common cooking oils (seed oils) to an aggressive form of breast cancer.

Introduction

Seed oils are everywhere. They’re in salad dressings, mayonnaise, chips, crackers, restaurant fryers, and even so-called “health foods.” But a growing number of doctors and nutrition experts are sounding the alarm: seed oils may be one of the most harmful ingredients in the modern diet. If you’re wondering why, this article will break it down in simple terms—no chemistry degree required.

What Are Seed Oils?

Seed oils are oils extracted from the seeds of certain plants, not from the fruit or flesh. The most common seed oils in our food supply are: Rice bran oil, Cottonseed oil, Corn oil, Grapeseed oil, Canola oil, Sunflower oil, Safflower oil and Soybean oil (often called the “Hateful Eight” because of their negative health effects).

The primary difference between seed oils vs. olive and avocado oils (aside from the fact that olives and avocados are fruits) is that the oils from olives and avocados are extracted by expeller-pressing the pulp of the fruit, not the seed.

The method in which seed oils are produced is a highly industrialized, chemically treated process that includes the following stages:

Stages Description
1. Cleaning/Preparation Seeds cleaned, dehulled, ground/flaked
2. Mechanical Pressing Initial oil extraction via screw/expeller press
3. Solvent Extraction Remaining oil extracted using hexane or similar solvents
4. Solvent Removal Oil/solvent mixture heated to remove and recover solvent using hexane
5. Refining Degumming, neutralization, bleaching, deodorization, sometimes winterization
6. Packaging Final refined oil is packaged for sale

How Did Seed Oils Take Over Our Food?

A century ago, most people cooked with butter, lard, tallow, or olive oil. But as food companies looked for cheaper, longer-lasting alternatives, they turned to seed oils. These oils are inexpensive to produce in massive quantities, and they don’t spoil as quickly as natural fats. Today, the average American gets up to 80% of their fat calories from these eight seed oils.

Why Are Seed Oils Bad for You?

1. Unstable Fats That Turn Toxic

Seed oils are loaded with a type of fat called polyunsaturated fatty acids (PUFAs). While a small amount of PUFA is necessary for health, the problem is that these fats are very unstable. When exposed to heat, light, or even just air, they break down and form toxic byproducts. This happens:

  • During the factory refining process

  • When you cook with them (especially frying)

  • Even when the bottle sits open in your kitchen

These toxic byproducts can damage your cells, promote inflammation, and contribute to a wide range of health problems.

2. Factory Processing Strips Away Nutrients

Nature protects the fragile fats in seeds with antioxidants and nutrients. But to extract oil from seeds, factories use harsh methods—high heat, pressure, and chemicals. This not only removes the natural nutrients but also creates more toxins in the process.

Even some “expeller-pressed” or “organic” seed oils can go through these damaging steps. The end result is a product that’s stripped of nutrition and full of unstable fats.

3. Seed Oils Promote Inflammation

When you eat seed oils, the unstable fats get built into your body’s cells and stored in your body fat. Over time, this can lead to chronic inflammation—a root cause of many modern diseases, including:

  • Heart disease

  • Diabetes

  • Obesity

  • Autoimmune conditions

  • Even some cancers

Inflammation is your body’s way of fighting off threats, but when it’s always “on,” it starts to damage healthy tissues. Seed oils are a major driver of this hidden inflammation.

4. They Disrupt Your Metabolism

Your metabolism is how your body turns food into energy. Seed oils can disrupt this process in several ways:

  • They make it harder for your body to burn fat for energy, leading to weight gain and fatigue.

  • They can make you crave more sugar and carbs, fueling a cycle of overeating.

  • They may even contribute to insulin resistance, a key factor in diabetes and metabolic syndrome.

Many people who cut out seed oils report more energy, easier weight loss, and fewer cravings.

5. They Weaken Your Immune System

A healthy immune system depends on a healthy metabolism. When your body fat is loaded with seed oil fats, your immune system is more likely to overreact, causing excessive inflammation. This can make infections more dangerous and recovery slower.

During the COVID-19 pandemic, doctors noticed that people with “metabolic problems” (often linked to high seed oil intake) were more likely to have severe outcomes.

6. They’re in Almost Everything

Seed oils are cheap, so food manufacturers use them in nearly all processed foods. Even foods labeled “organic” or “natural” often contain one or more of the Hateful Eight. Restaurant foods, especially fried items, are almost always cooked in seed oils.

Common Myths About Seed Oils

“Aren’t Seed Oils Heart-Healthy?”

For decades, organizations like the American Heart Association have promoted seed oils as “heart-healthy” because they lower cholesterol. But this advice is based on outdated, as well as possible manipulated, science and industry influence, not on solid evidence.

In fact, newer research (see reference links at bottom of article) shows that lowering cholesterol with seed oils does not reduce the risk of heart disease—and may even increase it by promoting inflammation and oxidative stress.

“What About Olive Oil, Coconut Oil, and Avocado Oil?”

Not all plant oils are bad. Olive, coconut, and avocado oils are mostly made from the fruit, not the seed, and contain more stable fats that don’t break down as easily. The key difference is how the oil is made and what kind of fat it contains:

Oil Type Source Main Fat Type Stability Health Impact
Olive Oil Fruit Monounsaturated Stable Good
Coconut Oil Fruit Saturated Very Stable Good
Avocado Oil Fruit Monounsaturated Stable Good
Seed Oils (H8) Seeds Polyunsaturated Unstable Bad

“Isn’t a Little PUFA Necessary?”

Yes, your body needs a small amount of PUFA, but the amount found in whole foods (like nuts, seeds, and fish) is enough. The problem is the massive excess from processed seed oils—far more than our bodies are designed to handle.

What Happens When You Cut Out Seed Oils?

Doctors who have helped patients cut out seed oils have seen dramatic improvements in diabetes, heart health, and even autoimmune conditions. Many people who remove seed oils from their diet report:

  • More energy and better mood

  • Easier weight loss

  • Fewer aches and pains

  • Improved blood sugar and cholesterol

  • Fewer cravings for sugar and junk food

  • Better skin and fewer allergies

How to Avoid Seed Oils

1. Read Ingredient Labels

  • Look for the Hateful Eight: Corn, Canola, Cottonseed, Soybean, Sunflower, Safflower, Grapeseed, Rice bran.

  • “Vegetable oil” on a label almost always means one or more of these.

2. Cook at Home with Healthy Fats

  • Use butter, ghee, olive oil, coconut oil, avocado oil, or animal fats like lard and tallow.

  • Make your own salad dressings and mayonnaise.

3. Choose Whole Foods

  • The fewer ingredients, the better. Whole foods like fruits, vegetables, meats, eggs, and dairy are naturally seed oil-free.

4. Be Careful When Eating Out

  • Most restaurants use seed oils for frying and sautéing. Ask if they can use butter or olive oil instead.

5. Avoid Processed and Packaged Foods

  • Traditional processed and packaged chips, crackers, cookies, and snacks often contain seed oils. If you are craving a snack, there are healthier, seed-oil-free alternatives listed on seedoilfreesnacks.co.

Frequently Asked Questions

  • Answer: The main problem is with the Hateful Eight (Corn, Canola, Cottonseed, Soybean, Sunflower, Safflower, Grapeseed, Rice bran), which are highly processed and high in unstable fats. Some seed oils, like unrefined peanut or sesame oil, are less harmful if used sparingly and not heated.

  • Answer: These methods are less harsh, but the oils are still high in unstable fats. They’re not as safe as traditional fats like butter, lard, tallow or olive oil.

  • Answer: Allergies aside, yes! Whole seeds and nuts are healthy. The problem is with the extracted, refined oils, not the foods themselves.

The Bottom Line

Seed oils are a modern invention, created by factories—not by nature. They’re cheap, convenient, and everywhere, but mounting evidence shows they’re a major driver of inflammation, metabolic problems, and chronic disease. The best thing you can do for your health is to avoid the Hateful Eight and choose natural, stable fats instead.

If you want to feel better, have more energy, and protect your long-term health, start by reading labels and making simple swaps in your kitchen. Your body will thank you.

Jason Merrill

Say hello to my passion project—Art Domain: the lovechild of art history and e-commerce that nobody knew they needed.

https://artdomain.co
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