Are Seed Oils Really That Bad?


“Are seed oils really that bad?” 

This is a question I get asked frequently. In this blog post I’m going to dive into seed oils and how they affect our health so that you can make an informed decision.

What Are Seed Oils?

Seed oil is a term used for any vegetable oil that comes from the seed of a plant. The most common are canola (rapeseed), sunflower, grapeseed, cottonseed, safflower, rice bran, peanut, soybean, sesame, flax, and corn oils. Most vegetable oils such as Wesson and Crisco are made from soybean, canola or a mixture of both and are technically seed oils. Examples of non-seed vegetable oils include olive oil, avocado oil, and coconut oil. 

What Types of Fats are in Seed Oils?

Seeds and seed oils are high in polyunsaturated fatty acids (PUFAs). There are two main PUFAs you have probably heard of: Omega-6 (linoleic acid or LA) and Omega-3 (alpha-linolenic acid or ALA). Both omega-6 and omega-3 are considered essential fatty acids (EFAs) which are necessary for optimal health and must be obtained though food because our body cannot produce them.

These two EFAs play many important roles in the body:

  • They are a critical component of cell membranes.
  • They are a major component of brain cell membranes and are involved in neurotransmitter signaling.
  • They play a role in blood clotting.
  • They help keep the skin barrier intact.
  • They are precursors to signaling molecules which play a role in the body’s inflammatory response, hormone production, and innate immune response.

EFAs, Prostaglandins and Inflammation

I’m going to dig into that last bullet point a bit more here. The role that omega-6 and omega-3 fatty acids play in the body’s inflammatory response is a big reason why we hear that seed oils are “bad” for us.

Omega-6 and omega-3 fatty acids are metabolized by enzymes in the body and can be converted to substances called prostaglandins which have hormone-like actions that can either promote inflammation or quell inflammation. Omega-6s can be turned into either anti-inflammatory Prostaglandin E1 or inflammatory Prostaglandin E2. Omega-3 can only be converted into anti-inflammatory Prostaglandin E3 (see diagram below). 

Too Much Omega-6 and Too Little Omega-3

Omega-6 and omega-3 compete for the same conversion enzymes as they follow along the pathways to form different prostaglandins. A diet high in omega-6 and low in omega-3 will increase inflammation in the body. A diet with a lot of omega-3 and not much omega-6 will reduce inflammation. So, the more omega-3 you eat, the less omega-6 will be available to the tissues to produce inflammation. 

While inflammation is a vital and natural part of our body’s response to injury and infection we can have too much of a good thing. Low-grade chronic or on-going inflammation is linked to a number of medical conditions such as Alzheimer’s disease, cancer, heart disease, IBD, autoimmune disorders, and type 2 diabetes.

The current Western or Standard American Diet (SAD) provides us with an abundance of omega-6s and very little omega-3s. Anthropological research suggests our hunter-gatherer ancestors who were free of modern inflammatory diseases (heart disease, cancer, diabetes) consumed omega-6 and omega-3 fats in a ratio of 3:1 or 1:1. The SAD that many people eat ranges anywhere from 10:1 to 25:1! It is this imbalance that that drives systemic inflammation and increases inflammatory disease risk. 

A large reason for this imbalance is our increased consumption of seeds and seed oils. Vegetable and seed oil consumption rose dramatically during the 20th century when the technology to extract them became available (Kresser, 2019). In addition to using these refined oils in cooking and baking they’re found in most processed foods (chips, breads/wraps, crackers, cookies, salad dressings, margarine, mayonnaise). Even the animal products we consume (meat, dairy, eggs) are high in omega-6s because conventionally raised feedlot animals are fed corn and soy because it’s cheap and fattens them up quickly. 

Other Concerns with Seed Oils  

PUFAs are highly unstable and oxidize easily when exposed to heat, light and air.  They are susceptible to oxidation both on the shelf and in your body. When you have a lot of PUFAs in your body (remember all of your cell membranes are composed of these fats!) you have a lot of fragile fatty acids that are more sensitive to oxidation. Oxidation produces harmful free radicals in the body, leading to oxidative stress and damage to cells, proteins, and DNA. 

The way in which most industrial seed oils are created is also of concern. Think of how small seeds are – it takes a lot of work to extract all of the oil out of them! First the seeds are often heated to high temperatures to reduce the moisture content. As you just learned, PUFAs are very fragile and oxidize when exposed to heat (not good). Next the seeds often have to go through synthetic chemical extraction methods using petroleum-based solvents like hexane to maximize the amount of oil extracted from them. The oil that is extracted tends to have such an off-putting smell that additional chemicals are used to deodorize them. This deodorizing process produces trans fats which are harmful to our health. 

Another concern is that seed oils are often repeatedly heated which makes them even more toxic. If you eat out at restaurants and consume fried foods (French fries, chicken fingers, wings, mozzarella sticks, poppers etc.) this is of concern. Most restaurants use seed oils in their deep fryers. Exposure to heat, light, and oxygen cause PUFAs to oxidize. To make things worse, the oil in deep fryers is often used over and over again, creating more and more free radicals. Deep frying of PUFAs also emits polycyclic aromatic hydrocarbons (PAH) and aldehydes, which are significant contributors to DNA mutation and cancer formation (Seed Oil Scout, 2022).

The Bottom Line: The way most industrial seed oils are produced, as well as the amounts most people are consuming in the Standard American Diet cause an imbalance in our omega-6 to omega-3 ratio that can lead to excess inflammation in the body. Inflammation is at the root cause of many medical conditions plaguing modern society. When we’re consuming industrial seed oils we’re consuming oils that contain chemical residues, trans fats, and oxidized by products – none of which are beneficial to our health.

How to Avoid Industrial Seed Oils

  • Replace any bottles of canola, corn, cottonseed, soybean, sunflower, safflower, or peanut oils with healthier cooking oils. Replace them with healthier fats, the types of fats our ancestors have used for thousands of years such as extra virgin olive oil, coconut oil, and animal fats from pasture raised animals (butter and ghee, lard, tallow, duck fat). 
  • Read ingredient labels and stop eating processed foods that contain them, or at the very least limit them. 
  • Reduce your consumption of restaurant foods, especially fried foods that are typically cooked in repeatedly heated seed oils. 
  • When eating out ask your server what types of cooking oils are used in food preparation. You can also download a free app called Seed Oil Scout – it can help you find restaurants that cook with healthy oils! 
  • Avoid eating grain-fed meat as much as you can. Source your animal products (meat, dairy, eggs) from 100% grass-fed and pasture raised animals. 

The types and amounts of fats we consume affect our health and wellness. I’ve helped people improve their weight, body composition, cholesterol and inflammatory markers through diet and lifestyle. If you would like help determining your current omega-6 to omega-3 ratio and how to improve it (if needed) please call or e-mail me to schedule a complimentary Nourish to Flourish Strategy Session! 


Kresser, C. (2019, February 19). How industrial seed oils are making us sick. Retrieved from

Seed Oil Scout (2022, November 16). The dangers of seed oils in deep fryers. Retrieved from

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