Content Library Longevity Journal

Are Seed Oils Bad for You? Here’s What You Need to Know

February 3, 2025

We’re in the midst of a heated health debate: Are seed oils really that bad for you?

Some argue they fuel chronic inflammation and modern disease. Others defend them as “heart-healthy,” citing evidence they help lower cholesterol and reduce heart disease risk.

At the core of this debate lies a key question: Is the real issue seed oils themselves, or simply how much we’re consuming? Or is it both?

And… what exactly are seed oils, anyway?

You might be eating them every day without realizing it. I’ll walk you through what they are, how they fit into modern diets, and what science really says about their impact on health. The answers may change the way you think about the oils you use.

What Are Seed Oils?

Seed oils (also known as plant-based or vegetable oils) are everywhere—used in processed foods, restaurant fryers, and home kitchens. They’re made from seeds, the oil-rich parts of plants like the germ of corn kernels or the soybean itself.

The most scrutinized of these oils, sometimes called the “hateful eight,” include canola, corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils.

How Are Seed Oils Made?

To extract these oils from their seeds, manufacturers rely on heavy industrial processes involving high heat, high pressure, and chemical solvents like hexane—a compound derived from petroleum. While most of the hexane is removed during production, trace amounts may remain in the final product.

Seed oils are widely used because they’re inexpensive to produce and have a long shelf life. Their neutral flavor and high smoke point—the temperature at which an oil starts to burn—also make them common choices for frying and high-heat cooking.

These refining methods are efficient but come at a cost: They can oxidize the oils and produce byproducts that may contribute to inflammation and other health risks.

Omega-6 Fats vs Omega-3 Fats

Seed oils are primarily made up of unsaturated fats, which stay liquid at room temperature. Most contain a high proportion of omega-6 fatty acids and relatively little omega-3s. Both are essential for health, but maintaining the right balance between them is key.

Here’s why: Omega-6 and omega-3 fats rely on the same enzymes to be converted into forms your body can use. Omega-6 fats help produce molecules that can promote inflammation when needed—such as to fight infections or repair injuries. 

Omega-3 fats, on the other hand, help produce compounds that reduce inflammation and support brain, heart, and overall cellular health. 

But when omega-6 intake is high—especially from linoleic acid in seed oils—these fats outcompete omega-3s for the available enzymes, limiting your body’s ability to convert omega-3s into their active forms.

When Omega-6 Dominate 

When omega-6 fats dominate your diet without enough omega-3s to counterbalance them, the inflammatory signals can overwhelm your body, leading to chronic, low-grade inflammation over time. 

Ideally, these fats would exist in balance. Historically, human diets contained roughly equal amounts of omega-6 and omega-3 fats, or at most, about four times as much omega-6. But with the rise of seed oils and processed foods, that ratio has skyrocketed—often reaching 10 times, 20 times, or even higher.

Why Does This Matter? 

Research shows that excess omega-6 fats, combined with insufficient omega-3s, can tilt your body into a constant state of low-grade inflammation.^1,2 This chronic inflammation has been linked to a host of health issues, including:

• Heart disease and diabetes
  
  
• Depression and cognitive decline
  
  
• Arthritis and other inflammatory conditions
  
  
• Obesity
  
  

The Overconsumption Problem

The real issue with seed oils isn’t just their composition—it’s how much of them you’re unknowingly consuming. Oils like soybean, corn, and sunflower are among the richest sources of omega-6 fats, and they’re everywhere in modern diets.

The biggest driver? Ultra-processed foods—everything from chips and crackers to frozen meals, salad dressings, and fast food. These products dominate the food landscape, making it easy to consume excessive amounts of omega-6 fats without even realizing it.

Between 1909 and 1999, linoleic acid intake—primarily from industrial seed oils like soybean and corn oil—increased more than 1,000 percent.³ And in recent decades, soybean oil consumption has continued to rise, with the average American now getting more than 3 tablespoons per day.

At the same time, many people don’t get enough omega-3-rich foods, such as wild-caught fish, flaxseeds, and walnuts, to help balance their intake. This imbalance has been linked to chronic inflammation, a key driver of many health issues.

Simply adding more omega-3s to your diet can help, but it doesn’t fully solve the problem if omega-6 intake remains excessively high. Cutting back on—or completely eliminating—ultra-processed foods and seed oils is just as important as increasing omega-3s.

Why Do Some Say Seed Oils Are Heart-Healthy?

For decades, major health organizations—including the American Heart Association (AHA) and the World Health Organization (WHO)—have promoted seed oils as a healthier alternative to saturated fats. 

This recommendation is primarily based on research showing that replacing saturated fats (found in butter, lard, and tropical oils) with polyunsaturated fats (PUFAs) can help lower LDL cholesterol, a risk factor for heart disease.^4,5

However, while PUFAs can help lower cholesterol, monounsaturated fats (MUFAs)—like those in olive oil and avocado oil—provide similar benefits without the excess omega-6.

This raises an important question: If MUFAs provide heart-health benefits without potential downsides, are seed oils really the best choice when you’re able to make the substitute yourself?

What’s more, because PUFAs are more chemically unstable than MUFAs or saturated fats, they’re more prone to oxidation when exposed to heat, which raises another concern: the formation of harmful byproducts.

Concerns About Toxic Metabolites

One of the main issues with seed oils is the potential for oxidation and toxic byproducts when exposed to high heat. Because of how PUFAs are chemically structured, they’re highly reactive under heat, light, and air, making them more likely to break down into harmful compounds during cooking. 

A major concern is the formation of aldehydes—highly reactive compounds that can damage cells and contribute to oxidative stress.

When seed oils are heated, particularly at frying temperatures, they break down into aldehydes, lipid peroxides, and oxidized linoleic acid metabolites (OXLAMs). Some animal studies suggest these byproducts may contribute to inflammation, metabolic dysfunction, and even cardiovascular and neurodegenerative diseases.⁶

While human research is still limited, the safest approach is to avoid using seed oils in high-heat cooking, opting instead for more stable fats like avocado oil, coconut oil, or ghee.

So, What Should You Do? 

Personally, I avoid seed oils and advise my patients to do the same. While there’s plenty of debate—and even outrage—on social media about this recommendation, let’s take a step back and look at what this actually means.

Most health experts agree that cutting back on ultra-processed foods is one of the best things you can do for your health. No one’s arguing with that. And when you follow that advice, you naturally eliminate a major source of seed oils from your diet. 

In that sense, avoiding seed oils isn’t some radical stance—it’s just a natural extension of choosing whole, minimally processed foods.

Beyond that, swapping seed oils for healthier alternatives when cooking at home is a simple, practical shift that also makes sense, especially if you want to err on the side of caution and get the most health benefits from your choice of oil. It doesn’t require an overhaul of your diet—just a few easy substitutions. Here’s how to get started:

• For high-heat cooking (like frying or roasting): Use avocado oil, ghee, or coconut oil, which have higher smoke points and better heat stability.
  
  
• For moderate-heat cooking (like sautéing): Both avocado oil and extra virgin olive oil are good options.
  
  
• For raw use (like dressings or drizzling): Cold-pressed oils such as extra virgin olive oil, walnut oil, and flaxseed oil are ideal. They’re perfect for finishing dishes or making dressings. Here are three easy salad dressings you can make at home.

So, to sum it up? Eat more whole foods, and choose the very healthiest oils. That’s not controversial—that’s just smart nutrition.

References                      

1. DiNicolantonio JJ, O'Keefe J. The Importance of Maintaining a Low Omega-6/Omega-3 Ratio for Reducing the Risk of Autoimmune Diseases, Asthma, and Allergies. Mo Med. 2021 Sep-Oct;118(5):453-459

2. Subošić B, Kotur-Stevuljević J, Bogavac-Stanojević N, Zdravković V, Ješić M, Kovačević S, Đuričić I. Circulating Fatty Acids Associate with Metabolic Changes in Adolescents Living with Obesity. Biomedicines. 2024 Apr 17;12(4):883

3. Blasbalg TL, Hibbeln JR, Ramsden CE, Majchrzak SF, Rawlings RR. Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. Am J Clin Nutr. 2011 May;93(5):950–62.

4. Ramsden CE, Zamora D, Leelarthaepin B, Majchrzak-Hong SF, Faurot KR, Suchindran CM, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ. 2013 Feb 4;346(feb04 3):e8707.   

5. Marklund M, Wu JHY, Imamura F, Del Gobbo LC, Fretts A, de Goede J, et al. Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality. Circulation. 2019 May 21;139(21):2422–36. 

6. Ganesan K, Sukalingam K, Xu B. Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers- A critical review. Crit Rev Food Sci Nutr. 2019;59(3):488–505.