What Are Seed Oils?

Seed oils are edible oils extracted from the seeds of various plants. Here are the key points about seed oils:

Common types of seed oils include:

canola oil (rapeseed oil)
corn oil
cottonseed oil (Crisco)
soybean oil
sunflower oil
safflower oil
grapeseed oil
rice bran oil
peanut oil

Key characteristics of seed oils:

They are high in polyunsaturated fats, particularly omega-6 fatty acids like linoleic acid.
They are often highly processed and refined using chemical solvents and high heat.
Their consumption has increased dramatically over the past century, especially in Western diets.

Potential Health Risks

linked to obesity by interacting with the endocannibinoid system
linked to metabolic syndrome and diabetes
increases the risk of cardiovascular disease
cause inflammation and chronic diseases related to them
disrupt the Omega-6 to Omega-3 balance in body
processing methods include harmful residual chemicals

Alternatives:

oils from the flesh of fruits: olive, avocado and coconut oils
beef tallow, lard, butter, ghee
focusing on whole, minimally processed foods

Citations:

[1] https://www.foodnetwork.com/healthyeats/healthy-tips/are-seed-oils-bad-for-you-healthy

[2] https://www.levels.com/blog/the-ultimate-guide-to-seed-oils-and-metabolic-health

[3] https://www.czapp.com/explainers/what-are-seed-oils/

[4] https://www.uhhospitals.org/blog/articles/2024/09/are-seed-oils-getting-a-bad-rap

[5] https://www.usatoday.com/story/life/health-wellness/2024/03/18/what-are-seed-oils/72856510007/

[6] https://www.massgeneral.org/news/article/seed-oils-facts-myths

[7] https://health.clevelandclinic.org/seed-oils-are-they-actually-toxic

[8] https://www.zeroacre.com/blog/seed-oils-to-avoid

Research

Deol P, Kozlova E, Valdez M, et al. Dysregulation of Hypothalamic Gene Expression and the Oxytocinergic System by Soybean Oil Diets in Male Mice. Endocrinology. 2020;161(2):bqz044.

“The 2 soybean oil diets had similar but nonidentical effects on the hypothalamic transcriptome, whereas the coconut oil diet had a negligible effect compared to a low-fat control diet. Dysregulated genes were associated with inflammation, neuroendocrine, neurochemical, and insulin signaling.”

Ramsden CE, Faurot KR, Carrera-Bastos P, et al. Dietary fat quality and coronary heart disease prevention: A unified theory based on evolutionary, historical, global, and modern perspectives. Curr. Treat. Options Cardiovasc. Med. 2009;11(4):289.

“As the source of virtually all structural and functional molecules in the human body, diet is perhaps the most important environmental determinant of health. Mounting evidence suggests that global populations with very low CHD rates share certain dietary characteristics, especially dietary fatty acid intakes.”

Lee JH, Duster M, Roberts T, et al. United States Dietary Trends Since 1800: Lack of Association Between Saturated Fatty Acid Consumption and Non-communicable Diseases. Front. Nutr. 2022;8:748847.

“Processed and ultra-processed foods increased from <5 to >60% of foods. Large increases occurred for sugar, white and whole wheat flour, rice, poultry, eggs, vegetable oils, dairy products, and fresh vegetables. Saturated fats from animal sources declined while polyunsaturated fats from vegetable oils rose. Non-communicable diseases (NCDs) rose over the twentieth century in parallel with increased consumption of processed foods, including sugar, refined flour and rice, and vegetable oils. Saturated fats from animal sources were inversely correlated with the prevalence of NCDs.”

Grootveld M, Percival BC, Grootveld KL. Chronic non-communicable disease risks presented by lipid oxidation products in fried foods. Hepatobiliary Surg. Nutr. 2018;7(4):305–312.

DiNicolantonio JJ, O’Keefe JH. Omega-6 vegetable oils as a driver of coronary heart disease: the oxidized linoleic acid hypothesis. Open Hear. 2018;5(2):e000898.

Alvheim AR, Torstensen BE, Lin YH, et al. Dietary linoleic acid elevates endogenous 2-arachidonoylglycerol and anandamide in Atlantic salmon (Salmo salar L.) and mice, and induces weight gain and inflammation in mice. Br. J. Nutr. 2013;109(8):1508–1517.

1.Alvheim AR, Malde MK, Osei-Hyiaman D, et al. Dietary Linoleic Acid Elevates Endogenous 2-AG and Anandamide and Induces Obesity. Obesity. 2012;20(10):1984–1994.

Alvheim AR, Torstensen BE, Lin YH, et al. Dietary Linoleic Acid Elevates the Endocannabinoids 2-AG and Anandamide and Promotes Weight Gain in Mice Fed a Low Fat Diet. Lipids. 2014;49(1):59–69.

Schuster S, Johnson CD, Hennebelle M, et al. Oxidized linoleic acid metabolites induce liver mitochondrial dysfunction, apoptosis, and NLRP3 activation in mice. J. Lipid Res. 2018;59(9):1597–1609.

Seed Oils are Highly Industrialized and Refined Products

How Are Seed Oils Made?

Seed oil production involves several key steps, combining mechanical and chemical processes to maximize oil yield and produce a clear, stable final product. Here’s a breakdown of the typical commercial process:

1. Seed Cleaning and Preparation

Seeds (such as canola, soybean, sunflower, or corn) are first cleaned to remove dirt, plant debris, stones, and metal fragments using screens, magnets, and gravity separators.
Some seeds are dehulled (removal of outer husks) for better oil quality.

2. Size Reduction and Conditioning

Seeds are often cracked or ground into smaller pieces to facilitate oil extraction.
The crushed seeds are then flaked (flattened) to rupture cell walls and increase surface area for extraction.

3. Cooking/Heating

The flaked seeds are heated or cooked to coagulate proteins, reduce oil viscosity, and improve extraction efficiency.

4. Mechanical Pressing

The cooked flakes are pressed using screw presses (expeller presses) to extract a portion of the oil. This produces crude oil and a residual press cake.
Mechanical pressing alone typically leaves 4–6% oil in the cake.

5. Solvent Extraction

To extract the remaining oil, the press cake is treated with a chemical solvent, most commonly hexane.
The solvent dissolves the oil, which is then separated from the solid meal. The meal (now low in oil) is often used as animal feed.
The oil-solvent mixture is heated to evaporate and recover the hexane, leaving the crude oil behind.

6. Oil Refining

The crude oil undergoes several refining steps:
- Degumming: Removal of phospholipids using water or acids.
- Neutralization: Removal of free fatty acids with caustic soda (sodium hydroxide).
- Bleaching: Removal of color pigments and impurities using bleaching clay or activated carbon.
- Deodorization: Steam injection at high temperatures to remove odors and volatile compounds.

7. Packaging

The refined oil is filtered, cooled, and packaged for sale as cooking oil or for use in processed foods.

Cold Pressing: Some specialty oils are made using only mechanical pressing at low temperatures, avoiding solvents and extensive refining.
Supercritical CO₂ Extraction: Used for niche or gourmet oils, this method uses carbon dioxide under high pressure as a solvent.

Citations:

Main Chemicals Used in the Processing of Seed Oils

1. Hexane (Solvent Extraction)

Hexane is the primary chemical solvent used to extract oil from seeds such as soybean, canola, sunflower, cottonseed, and peanut. Seeds are ground and mixed with hexane, which dissolves the oil. The hexane is later evaporated and recovered, leaving the oil behind.

2. Acids (Degumming)

Phosphoric acid or citric acid is commonly used during the degumming step to remove phospholipids ("gums") from crude oil4. These acids help break down nonhydratable phospholipids, which are then removed by centrifugation or adsorption with bleaching earth.

3. Caustic Soda (Sodium Hydroxide, NaOH)

Caustic soda is used in the neutralization process to remove free fatty acids from the oil, forming soap that is then separated from the neutral oil.

4. Bleaching Agents

Bleaching clays, activated carbon, and special silicas are used to adsorb and remove pigments (such as carotenoids and chlorophyll), residual soaps, and other impurities during the bleaching stage.

5. Water and Enzymes

Water is used in various washing steps to remove residual soaps and impurities. Enzymes may be used in enzymatic degumming to hydrolyze phospholipids.

6. Steam (Physical Refining/Deodorizing)

High-temperature steam is used under vacuum to deodorize the oil, removing volatile compounds that contribute to undesirable odors and flavors.

Citations:

Are seed Oils Bad for You?

All seed oils contain Omega-6 fatty acids. These are polyunsaturated fats which are liquid at room temperature. Polyunsaturated fats are much more easily oxidized than saturated fats. The main Omega-6 fatty acid in seed oils is linoleic acid. When it is oxidized it produces OxLams.

OxLams (Oxidized Linoleic Acid Metabolites) are bioactive compounds formed when linoleic acid (LA), a common dietary polyunsaturated fatty acid, undergoes oxidation. These metabolites include 9- and 13-hydroxy-octadecadienoic acid (HODE) and 9- and 13-oxo-octadecadienoic acid (oxoODE)1.

They are implicated in various pathological conditions such as cardiovascular disease, chronic pain, Alzheimer's dementia, and non-alcoholic steatohepatitis (NASH). OxLams contribute to inflammation, oxidative stress, and cellular dysfunction by acting as signaling molecules and can promote disease progression through mechanisms like activating TRPV1 pain receptors and inflammasomes in the liver1 2 4.

OxLams are found in oxidized foods like heated vegetable oils and processed foods, and they can accumulate in the body, leading to metabolic and mitochondrial dysfunction over time, which may contribute to chronic diseases and metabolic syndrome prevalent in modern populations3 8.

In summary, OxLams are harmful oxidized derivatives of linoleic acid linked to inflammation, oxidative stress, and chronic disease development1 3 4.

Citations:

Seed Oils Cause Mitochonrial Dysfunction

Oxidized linoleic acid metabolites (OXLAMs) cause mitochondrial dysfunction through several interconnected mechanisms:

Reduced Complex I Protein and ATP Levels: OXLAMs decrease the amount of mitochondrial Complex I protein and lower hepatic ATP production, directly impairing the mitochondria’s ability to generate energy1 2.
Increased Oxidative Stress: OXLAMs elevate oxidative stress in cells, leading to damage of mitochondrial components and depletion of antioxidant defenses1 3 5.
Activation of Apoptosis Pathways: They increase thioredoxin-interacting protein (TXNIP) and activate mitochondrial apoptosis signal-regulating kinase 1 (ASK1), triggering cell death pathways1 2.
NLRP3 Inflammasome Activation: OXLAMs promote activation of the NLRP3 inflammasome and Caspase-1, which are linked to inflammation and further mitochondrial injury1 2.
Disrupted Redox Balance: These metabolites disrupt mitochondrial redox homeostasis, making mitochondria more vulnerable to further stress and dysfunction3 5.

Together, these effects lead to impaired energy production, increased cell death, and inflammation, contributing to diseases like nonalcoholic steatohepatitis (NASH) and heart muscle fibrosis1 2 5.

Citations:

But Don’t Seed Oils Lower LDL - The Bad Cholsterol?

Yes, seed oils-such as sunflower, safflower, canola, soybean, and flaxseed oils-are well-established in scientific studies to lower LDL cholesterol (“bad cholesterol”) when they replace saturated fats like butter, lard, or ghee in the diet. This effect is primarily due to their high content of polyunsaturated fats, which enhance the liver’s ability to clear LDL particles from the blood.

Key findings from research:

Multiple meta-analyses and clinical trials show that switching from saturated fats to unsaturated fats found in seed oils consistently lowers LDL cholesterol levels1 4 5 6.
Oils such as safflower, sunflower, rapeseed (canola), and flaxseed performed best at lowering LDL in comparative studies1 4 6.
This LDL-lowering effect is robust and one of the most consistent findings in nutritional science over the past several decades5 6.

However, it is important to note:

Lowering LDL cholesterol is just one aspect of heart health. The overall risk of heart disease depends on many factors, including HDL cholesterol, triglycerides, blood pressure, inflammation, and the oxidation status of LDL particles2.
Some experts caution that while seed oils lower LDL, polyunsaturated fats can make LDL particles more prone to oxidation, which may increase cardiovascular risk if the diet is otherwise unhealthy or high in processed foods2.
Extra virgin olive oil, rich in monounsaturated fats and antioxidants, also lowers LDL but is associated with additional heart health benefits, such as raising HDL (“good cholesterol”) and reducing inflammation2 4.

Citations:

Oxidation of Saturated Fats

The oxidation of saturated fats before reaching consumers is influenced by factors like food processing, storage conditions, and inherent fat stability. While specific quantitative percentages are not explicitly provided in current research, here's a synthesis of key findings:

Stability of Saturated Fats

Chemical resistance to oxidation: Saturated fats are structurally more stable than unsaturated fats due to the absence of double bonds, making them less prone to oxidative rancidity during storage and processing8 14. Polyunsaturated fats, by contrast, oxidize more readily and form harmful compounds like lipid hydroperoxides6 8.
Food matrix protection: In whole foods like dairy and unprocessed meat, saturated fats are embedded in a protective matrix that further slows oxidation10 11.

Industry Practices

Antioxidant use: Processed meats and foods high in saturated fats often include antioxidants (natural or synthetic) to delay oxidation during shelf life6.
Reformulation challenges: Efforts to replace saturated fats with unsaturated alternatives (e.g., omega-3-enriched products) face oxidation-related shelf-life issues, highlighting the relative stability of saturated fats6.

Post-Consumer Oxidation

Metabolic oxidation: Once consumed, saturated fats are oxidized less efficiently than unsaturated fats in the human body. For example, postprandial fat oxidation rates are lower after meals rich in saturated fats compared to monounsaturated fats5 10.

In summary, while saturated fats are less susceptible to oxidation than unsaturated fats, exact pre-consumer oxidation percentages remain unquantified in the literature. Their stability makes them less likely to oxidize significantly under typical storage conditions, but this depends on food handling practices6 8 14.

Citations:

Its important to note that LDL is NOT cholesterol. Cholesterol is a specific molecule found in every cell in the body. It is mainly utilized in cells walls to alter the cells flexibility. It is a vital component of brain cells. LDL stands for Low Density Lipoprotein. These lipoproteins come in various sizes such as very low density (VLDL), low density (LDL), high density (HDL). They are made in the liver and carry fat soluble molecules, including cholesterol, throughout the body, as fats are not soluble in water (blood). Thus, LDL, in and of itself, is not bad for you. It is an absolutely necessary cargo container for your body. However, if it becomes OXIDIZED, then it changes it shape to become small and dense and loses it receptor necessary for the liver to take it back up. Seed oils that are not oxidized are not harmful. But seed oils are EASILY oxidized, especially compared to saturated fats. And when oxidized seed oils are packaged in VLDL in the liver (which eventually becaome LDL) it oxidizes the LDL and becomes harmful.

Oxidation of Seed Oils by the Time They Reach the Consumer

Seed oils, particularly those high in polyunsaturated fatty acids (PUFAs), are inherently prone to oxidation. Oxidation can occur during processing, storage, transportation, and even after the oil is opened at home. Factors such as exposure to heat, light, and oxygen accelerate this process, leading to the formation of primary (peroxides) and secondary (aldehydes, ketones) oxidation products6 8 12.

Quantitative Estimates from Research

Peroxide Value (PV) as a Marker: Peroxide value is a standard measure of primary oxidation in oils. Fresh, high-quality seed oils typically have PVs below 10 meq/kg. Values between 10–20 meq/kg indicate the early stages of oxidation, and above 20 meq/kg is considered rancid and unsuitable for consumption5.
Storage Studies: Research shows that seed oils stored at room temperature without sunlight reach about half the threshold for rancidity (i.e., PV around 10 meq/kg) after 90 days. If exposed to sunlight, oxidation accelerates, with PVs reaching 23.5 meq/kg in the same period5.
Shelf Life and Supply Chain: Considering the time from production, bottling, transportation, shelving, and eventual purchase, many seed oils may spend several months before reaching the consumer. The oxidation process is generally linear, and oils can approach or exceed the early oxidation stage (10–20 meq/kg) by the time they are purchased, especially if not stored optimally5 2.

Percentage of Oxidized Seed Oils

General Estimate: While exact percentages vary by oil type, storage conditions, and handling, studies indicate that a significant portion of seed oils on store shelves show measurable oxidation. For example, a study on avocado oil (which is compositionally similar to some seed oils) found that 15 out of 22 samples were oxidized before their expiration date, suggesting that over 68% were at least partially oxidized9.
Seed Oil-Specific Data: For seed oils like soybean, canola, and grapeseed, research indicates that after several months of typical storage, oils can be halfway to rancidity (i.e., 50% of the way to the peroxide value considered unfit for consumption)5. This suggests that a substantial fraction-potentially 30–50%-of the oil’s oxidizable content has been affected by the time it reaches the consumer, though not necessarily to the point of being considered fully rancid.

Key Takeaways

A significant portion (30–50%) of seed oils are partially oxidized by the time they reach the consumer, especially if stored for several months under typical conditions5 9 2.
Most commercially available seed oils do not exceed regulatory limits for oxidation, but measurable oxidation is common2 5.
Storage conditions (light, heat, air exposure) play a critical role in the rate and extent of oxidation5 6 12.
Adulteration and blending with older oils can increase the percentage of oxidized oils in the marketplace9.

In summary, while most seed oils on store shelves are not fully rancid, a substantial proportion are at least partially oxidized by the time they reach the consumer, with estimates ranging from 30% to over 60% depending on the oil type and storage conditions5 9 2.

Citations:

What Are Seed Oils?

Research

Seed Oils are Highly Industrialized and Refined Products

How Are Seed Oils Made?

Main Chemicals Used in the Processing of Seed Oils

Are seed Oils Bad for You?

Seed Oils Cause Mitochonrial Dysfunction

But Don’t Seed Oils Lower LDL - The Bad Cholsterol?

However, it is important to note:

Oxidation of Saturated Fats

Stability of Saturated Fats

Industry Practices

Post-Consumer Oxidation

Oxidation of Seed Oils by the Time They Reach the Consumer

Key Takeaways

With knowledge, one can see clearly