Are Seed Oils Bad For You?

diet fat keto paleo whole 30 Apr 08, 2023
By Dr. Patrick Zitt, DC, DNM, MS



Seed oils are a huge source of controversy in the food and nutrition world. Cheap and easily accessible, they no doubt provide a means to more affordable food. There are a handful of studies that support mainstream claims that these oils are okay to include in a balanced diet. However, there are piles of evidence demonstrating the negative health effects of these oils, and that should give us all pause when making smart consumer choices. 


What are seed oils?

Seed oils (also referred to as vegetable oils or industrial oils) are unsaturated oils made from crops such as soybean, corn, sunflower seeds, safflower seeds, cottonseed, rapeseed/canola, grapeseed, and rice bran.

Unlike coconuts or olives, these crops do not easily give up their oils. After the seeds are gathered, they require extensive processing before the desired result is achieved:

  1. The seeds are first heated to extremely high temperatures, oxidizing* the oils in the process.
  2. To get the greatest yield of oil, they are then treated with a petroleum-based solvent, usually hexane. (An exception to this is when oil is expeller pressed, which uses mechanical extraction instead of chemical solvents.)
  3. Finally, because oxidation has caused them to look and smell foul, they are treated with various chemicals, bleaches, and deodorizers to improve their appeal.


*Oxidization, also known as “going rancid”, is a series of chemical reactions caused by heat, light, or oxygen that degrades the quality of the oil. It produces harmful compounds and toxic by-products.


Primary sources of seed oils

Due to their very low cost, seed oils are found in the majority of packaged foods that contain added fats or oils:

  • Baked goods
  • Candy
  • Coffee creamer
  • Crackers and chips and other snacks
  • Dairy free cheese
  • Frosting
  • Frozen fried foods
  • Granola and protein bars
  • Ice cream
  • Margarine and shortening
  • Marinades
  • Mayonnaise
  • Nut milks
  • Popcorn
  • Salad dressings

In addition to items found at the store, you can almost guarantee you are consuming high amounts of seed oils in your fast food and restaurant meals.


The negative health affects of seed oils

Consumption of these industrialized oils has been linked to an array of health problems:

  • Asthma (1)
  • Autoimmune Disease (2)
  • Depression, anxiety, dementia, and aggression (34567)
  • Diabetes, obesity, and fatty liver disease (8, 91011)
  • Dysbiosis (poor gut health) (121314)
  • Heart Disease (151617)
  • Inflammation (1819)
  • Infertility (202122)
  • Macular Degeneration (23)
  • Osteoarthritis (24)

While seed oils are certainly not the only contributing factor, for those trying to address these conditions, it may be the missing piece to the puzzle.


Okay, but why are they bad?

How could something as simple as an oil have such a negative impact on our health? Well, I’m glad you asked.


Seed oils promote inflammation

There are two Polyunsaturated Fatty Acids (PUFA): Omega-3 and Omega-6. Our bodies require both from our diet in a careful balance.

Omega-3 fatty acids are anti-inflammatory. You can read more about the pro health benefits of Omega-3 fatty acids here.

Omega 6-fatty acids play a role in brain function, hair growth, bone health, metabolism, and the reproductive system. They are also pro-inflammatory. Under normal circumstances, inflammation is a  healthy reaction to harmful stimuli (such as an injury or illness) and initiates the healing process.

But too much inflammation or chronic inflammation (not in response to an acute trigger) is what gives rise to the host of health problems we are discussing here.

Ideally, we would consume just as much Omega-3 fatty acids as Omega-6 fatty acids, if not more. Unfortunately, predominately due to the prevalence of industrial seed oils, the standard American consumes an average of 16x more Omega-6 fatty acids! (25)

This imbalance leads to the inflammation that triggers insulin resistance (can lead to diabetes), leptin resistance (can lead to obesity), and endothelial dysfunction (can lead to heart disease). (26272829

In addition to the negative PUFA ratio inherent to these oils, high heat processing and cooking produces byproducts such as oxylipins, which promote oxidative damage and further inflammation inside the body (30). 


Seed Oils Promote Fat Storage and Obesity

Linoleic acid, a type of Omega-6 fatty acid, encourages fat tissue to increase insulin-sensitivity, absorbing more glucose from the blood, converting it into triglycerides, and finally storing it as fat.  (31)

Linoleic acid can may also encourage one to eat past the point of satiety by altering neurotransmitter signaling. One animal study, where mice were fed a high soybean oil or a coconut oil diet demonstrated that those on the soybean oil diet had significant increases in fat accumulation, weight gain, diabetes, and insulin resistance (32).


Seed oils oxidize easily

Thanks to their chemical structure, seed oils (polyunsaturated fatty acids) are more prone to oxidation, especially compared to saturated fats and monounsaturated fats. Oxidation is the process that is initiated upon elevated exposure to heat, light, or oxygen. When oxidation occurs, a few harmful substances are created:

  •  Trans fats - It is (finally) well known that trans fats from hydrogenated oils, like margarine and Crisco, contribute to diabetes and heart disease, and have now been outlawed in the US. However, due to the oxidation that occurs in the refining process, un-hydrogenated (liquid) seed oils can contain up to 4.2 percent trans fats. (3334) This number can increase as further oxidation occurs due to high heat cooking or improper storage.
  • Lipid peroxides - When the Omega-6 in our cell membranes is increased, lipid peroxidation occurs. Lipid peroxides are toxic byproducts that damage DNA and proteins which may lead to aging, chronic disease, and cancer. (35)

To make matters worse, restaurants and fast food establishments (and some frugal home cooks) routinely reuse seed oils, repeatedly heating them to the point of oxidation. The more these oils are heated, the more toxic byproducts and DNA damaging free radicals can accumulate. Repeatedly heated oils have been associated with heart disease, high blood pressure, and liver and intestinal damage. (363738)


Lastly, seed oils are void of nutrients

I believe the majority of people are not purposefully consuming seed oils, so this may be a moot point. However, what little nutrients these oils may have contained are eliminated during processing, leaving them with nothing but calories.

There are many whole food sources of dietary fat that are accompanied by vitamins, minerals, phytonutrients, fiber, and other wonderful qualities:

  • Avocado
  • Eggs
  • Fatty fish
  • Full fat, grass fed dairy (if you tolerate it)
  • Nuts and seeds
  • Olives

When selecting cooking oils for your home, opt for these oils which are less processed, retain more nutrients and antioxidants, and have a more beneficial fatty acid profile:

  • Extra virgin olive oil
  • Avocado oil
  • Grass fed butter or ghee
  • Coconut oil
  • Animal fats (lard, tallow, etc)
  • Cold pressed nut oils

Check out this article where we have expanded on the benefits of healthy oils.


Avoiding seed oils

Now that you understand the importance of avoiding industrial seed oils, you're probably wondering how.

The solution is simple, though not easy: Read labels in the store and make as much of your food from scratch.

Avoid products with soybean oil, corn oil, sunflower oil, safflower oil, cottonseed oil, canola oil, grapeseed oil, and rice bran in the ingredient list, when possible.

With some research, you can find store bought packaged items that do not contain seed oils. My favorite brand of dressings, spreads, and marinades is Primal Kitchen. Instead, they favor avocado oil (in fact, the majority of their products are Paleo and Whole30 approved).

For the items you cannot find grocery store swaps for, try your hand at making it yourself. It may be a fun family project to make your own nut milk or ice cream! And homemade mayo is surprisingly easy.


But here's a reality check

I am a busy man with a busy wife and young kids and a business and a yard to mow...

I need the occasional convenience food. I eat Chick-fil-A when I travel. I enjoy Ruffles at a BBQ. I'm human, and so are you. 

The point is to be mindful of these ingredients and avoid when possible. It is NOT to be perfect, avoid at all costs, or stress yourself out over yet another item in a growing list of ingredients you should avoid (unless you have a condition that would greatly benefit from strict avoidance or have been otherwise advised by your healthcare professional).

Seed oils can cause inflammation....but so can stress.


Just for fun: A quick history on seed oils

In the mid 19th century, Proctor & Gamble was using cottonseed oil in their famous soaps. When they discovered the patented hydrogenation process that turned liquid cottonseed oil into a solid, Crisco was born. Marketed as a healthy and inexpensive alternative to butter, Crisco became a household staple.

In 1948, P&G donated a hefty sum to the then new American Heart Association (AHA). Shortly thereafter, the AHA began recommending that Americans replace saturated fats (like butter) with “heart healthy” seed oils (that’s right, Crisco).

The AHA’s recommendations coincided with president Eisenhower’s first heart attack. Physiologist Ancel Keys attended to him and concluded it was due to the consumption of saturated fat and cholesterol. He then recommended that the American public make a swift switch to vegetable oils, on the cover of Time Magazine, no less. Unfortunately, his conclusion was based on faulty research of poorly conducted studies.

It wasn’t until the 1990’s that the AHA changed their tune on hydrogenated oils (trans fats), though they continue to recommend non hydrogenated seed oils.


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