The Most Unhealthy Oils to Cook With: Insights from Functional Medicine

The consensus among these voices is clear: seed oils, derived from crops like corn, soy, and canola, dominate the “unhealthy” list due to their high omega-6 content, chemical extraction processes, and instability under heat. These factors lead to cellular damage, hormonal imbalances, and even links to conditions like diabetes and autoimmune disorders. Let’s dive into the most problematic oils, backed by insights from these experts. What Makes an Oil Unhealthy?

A Functional Perspective

Before listing specific oils, it’s essential to understand the criteria used by functional medicine doctors. Dr. Will Cole, a leading functional medicine expert, explains that industrial seed oils are among the top “unhealthy ‘health’ foods” because they are ubiquitous in processed products and falsely labeled as beneficial.  

These oils are typically extracted using high heat, chemical solvents like hexane (a neurotoxin), and deodorizers that mask rancidity. This process not only strips nutrients but also creates harmful byproducts, including trans fats and oxidized lipids.A key issue is the omega-6 to omega-3 ratio. Humans evolved on diets with roughly equal amounts of these fatty acids, but modern seed oils skew this to 20:1 or higher, promoting chronic inflammation—a root cause of many diseases, according to Chris Kresser and other alternative advisors. When heated for cooking, these polyunsaturated fats (PUFAs) break down into aldehydes and other compounds that damage DNA and proteins. Functional Medicine University highlights how omega-6-rich oils like corn and soy create harmful byproducts during cooking, exacerbating oxidative stress. Continued after this next fast clip on Canola Oil Poison…

5. Cut out seed oils.

They’re poison. They have excess linoleic acid and are prone to oxidation leading to:

– Pro-inflammatory molecules
– Toxic aldehydes and lipid peroxides

Which cause cell damage, oxidative stress, and inflammation… pic.twitter.com/QpihFhoIlo

— Ábris Babicz | The Demi Cycle Protocol 🧬 (@AbrisGains) March 3, 2025

Alternative health experts also point to genetic modification (GMOs) in crops like soy and canola, which introduce pesticides and alter fat profiles. Dr. Josh Axe warns that vegetable oils’ high omega-6 content alone is a major disadvantage, contributing to inflammation and poor heart health—contrary to conventional claims. Moreover, these oils are often partially hydrogenated, forming trans fats that Dr. Mark Hyman describes as “shortening your life,” ruled unsafe by even regulatory bodies. In podcasts and writings, Hyman repeatedly calls out refined oils as drivers of metabolic dysfunction, urging avoidance for better brain health and longevity.

Functional practitioners unanimously advise ditching them for cooking, frying, or even salad dressings.

1. Canola Oil: Derived from rapeseed, canola is heavily processed with chemicals and often GMO-sourced. Dr. Axe criticizes its omega-6 overload, which disrupts hormonal balance and promotes inflammation. Functional Medicine University adds that heating canola produces harmful byproducts.
2. Soybean Oil: Ubiquitous in processed foods, soybean oil is another GMO heavyweight high in omega-6s. Hyman warns it’s a key inflammatory culprit in modern diets, worsening brain fog and aging. Dr. Cole includes it in his list of deceptive “health” ingredients that sabotage wellness. Alternative expert Michael Morelli (@morellifit) brands it “pure poison,” citing its industrial origins and metabolic harm.
3. Corn Oil: Extracted from corn kernels, this oil is unstable at high temperatures, leading to aldehyde formation. Shanahan lists it first among unhealthy options due to its pro-inflammatory effects. Integrative sources explain its evolutionary mismatch, as humans didn’t consume concentrated corn fats historically. Kim Johnson, a functional nutritionist ( @Twisted_Veggies), highlights how heat damages corn oil, impairing mitochondrial function.
4. Sunflower Oil: High in linoleic acid (an omega-6), sunflower oil oxidizes easily, creating free radicals. Dr. Steven Belknap (@StevenMBelknap) advises against it for frying, noting aldehyde production that damages molecules. Functional Medicine University includes it in toxic seed oils for byproducts harmful to health. O’Neill warns of its instability when heated.
5. Safflower Oil: Similar to sunflower, safflower is PUFA-heavy and prone to rancidity. Shanahan and Axe both flag it for inflammation and poor stability. Alternative advisors like Oliver Anwar (@theoliveranwar) group it with seed oils to avoid, favoring natural alternatives.
6. Cottonseed Oil: Often hydrogenated, this oil contains gossypol (a toxin) and high omega-6s. Shanahan calls it out as particularly unhealthy, with residues from pesticide-heavy cotton crops. Johnson notes its toxic chemical release upon heating.
7. Grapeseed Oil: Marketed as gourmet, but high in PUFAs and processed with solvents. Functional experts like Cole warn it’s no better than other seeds, disrupting omega balance. Morelli and others label it inflammatory.
8. Rice Bran Oil: Less common but rising, it’s unstable and omega-6 laden. Shanahan includes it for similar reasons: oxidation and health risks. Johnson adds it to avoided lists for mitochondrial damage. “Vegetable oil” blends often combine these, amplifying issues. Hyman stresses avoiding all refined oils for detoxification and anti-aging. Experts like Frederick Bellamy (@DextertheCatX5) advocate traditional fats like tallow over these.  Continued below this next clip by Gary Brecka

You’re cutting sugar, eating more protein, even hitting the gym, but you still feel inflamed? The real issue could be seed oils. Originally used as machine lubricants, seed oils (vegetable oils) were never designed for human consumption. They’re toxic by design, oxidized, inflammatory, and metabolic disruptors. 

You’re cutting sugar, eating more protein, even hitting the gym, but you still feel inflamed?

The real issue could be seed oils. 🚫

Originally used as machine lubricants, seed oils (vegetable oils) were never designed for human consumption. They’re toxic by design, oxidized,… pic.twitter.com/OG1hMnFsMj

— Gary Brecka (@thegarybrecka) June 5, 2025

Broader Implications and Alternatives

The overconsumption of these oils correlates with rising obesity and disease rates, per functional medicine. Advisors recommend saturated fats like coconut oil, butter, ghee, and tallow for cooking stability. Dr. Axe and Hyman suggest olive or avocado for low-heat uses, but caution against frying.

By heeding these warnings, individuals can reduce inflammation, support metabolic health, and align with ancestral eating patterns. Functional medicine empowers proactive choices—starting with your kitchen oils.

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