Health Nutrition Science
Mark Hyman, M.D.
Mark Hyman, M.D.

@drmarkhyman

10 tweets 14 reads Feb 11, 2025
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Seed oils: toxic or heart-healthy?
The debate is explosive, but the truth is clear—here’s what the science really says. 🧵👇
We’re consuming more seed oils than ever before—often without realizing it.
The average American now consumes over three tablespoons of soybean oil per day.
Between 1909 and 1999, linoleic acid intake (primarily from seed oils like soybean and corn) increased by more than 1,000 percent.
Research shows that this shift in fat consumption is a key driver of chronic inflammation, metabolic dysfunction, and disease
Seed oils, also known as vegetable oils, are extracted from the oil-rich parts of plants like soybeans, corn, and sunflower seeds.
The most scrutinized of these, often called the “hateful eight,” include:
-Soybean oil
-Corn oil
-Canola oil
-Cottonseed oil
-Sunflower oil
-Safflower oil
-Grapeseed oil
-Rice bran oil
They are cheap to produce, have a long shelf life, and are found in nearly all ultra-processed foods, fast food, and restaurant cooking oils.
Not all oils are created equal. It’s not just about the oil itself—but how it’s extracted.
Cold-pressed oils—like extra virgin olive oil—are made with minimal processing. The oil is simply squeezed out of the seed or fruit.
But industrial seed oils go through multiple refining steps, including high heat, chemical extraction, and deodorization. This process damages the fats, creates harmful byproducts, and strips away beneficial compounds.
Seed oils undergo a highly industrialized process that makes them cheap and shelf-stable—but also damaging to health.
These oils are known as RBD oils—Refined, Bleached, and Deodorized.
Here’s what happens:
-Refining: High heat and chemical solvents (like hexane) extract the oil.
-Bleaching: Removes color and impurities—but also beneficial antioxidants.
-Deodorization: Exposes the oil to extreme heat, creating trans fats and oxidation byproducts.
These oils are then used in ultra-processed foods, fried foods, salad dressings, and packaged snacks.
Seed oils are extremely high in omega-6 fats—especially linoleic acid—which can promote inflammation when consumed in excess.
Historically, human diets contained a nearly equal balance of omega-6 to omega-3 fats. Today, due to seed oil overconsumption, that ratio has skyrocketed to 10:1, 20:1, or even higher.
This imbalance blocks omega-3s from being converted into their active, anti-inflammatory forms—fueling systemic inflammation over time.
Chronic, low-grade inflammation has been linked to:
-Cognitive decline and depression
-Heart disease and diabetes
-Autoimmune conditions
-Metabolic dysfunction and obesity
Excess omega-6 fats—especially from linoleic acid in seed oils—tilt your body into a constant state of inflammation.
Seed oils aren’t just fats. They also contain:
-Emulsifiers that disrupt gut health and increase inflammation.
-Hidden added sugars that drive overconsumption and metabolic dysfunction.
-Highly oxidation-prone fats that generate toxic byproducts when heated.
This leads to chronic hunger, blood sugar imbalances, and long-term health consequences.
When seed oils are exposed to high heat (like in frying), they break down into harmful compounds, including:
-Aldehydes – highly reactive molecules linked to oxidative stress and disease.
-Lipid peroxides – unstable fats that can damage cells.
-Oxidized linoleic acid metabolites (OXLAMs) – implicated in cardiovascular and neurodegenerative diseases.
Some of these byproducts may contribute to inflammation, metabolic dysfunction, and cellular damage.
I avoid seed oils and advise my patients to do the same.
-Cut back on ultra-processed foods—the biggest source of hidden seed oils.
Choose healthier cooking oils:
-For high-heat cooking: Avocado oil, ghee, coconut oil
-For moderate-heat cooking: Extra virgin olive oil, avocado oil
-For raw use: Cold-pressed olive oil, walnut oil, flaxseed oil
Check your omega-6 to omega-3 ratio. Comprehensive testing—like the one offered at Function Health—can help you track your levels and make targeted dietary changes.

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