The Evidence on Seed Oils
Don't take our word for it. Below is the free, readable evidence on seed oils — 62 sources organized by type: the controlled trials, the mechanism, a century of rising intake, what heat does, the metabolic and organ research, and the population studies that cut the other way. Every link opens something you can read or watch for nothing. Read it and decide for yourself.
Is the science settled? No — and we'll say so
This is an honest page, not a one-sided one. The strongest controlled trials that actually fed people seed-oil linoleic acid, plus the mechanism and animal work, point toward harm. But most large observational studies that measure linoleic acid in the body find it neutral or even protective. We show you both, labeled, so you can weigh the real evidence instead of a sales pitch. Lower is still our bet — but you should read and decide for yourself.
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Ray Peat, Ph.D.
The biologist and endocrinologist who first made the case, in plain writing, that the polyunsaturated fats in seed oils quietly damage metabolism and health. For this community, he is where it started — and all of his work is free to read.
The trials that swapped them in
In the two best controlled trials that replaced saturated fat with seed-oil linoleic acid, cholesterol fell — but people did not live longer, and the seed-oil groups actually had more deaths. Both are peer-reviewed and open-access.
Start Here: Ray Peat
The biologist whose writing put polyunsaturated seed oils at the center of this whole conversation. Everything on his site is free to read.
| Source | Type |
|---|---|
| Unsaturated Vegetable Oils: Toxic Ray Peat, Ph.D. · His foundational essay — why the polyunsaturated fats in seed oils suppress metabolism, the thyroid, and the immune system. The piece most people start with. | FREE |
| The Great Fish Oil Experiment Ray Peat, Ph.D. · Why "healthy" polyunsaturated oils — including fish oil — drive the same oxidation damage as the seed oils they were supposed to replace. | FREE |
| Every Ray Peat article (full archive) Ray Peat, Ph.D. · His complete library of free articles on fats, hormones, metabolism, and health. Decades of writing, all openly available. | FREE |
The Controlled Trials
The strongest evidence is not opinion — it is the randomized trials that actually swapped saturated fat for seed-oil linoleic acid and followed what happened. In the best-run ones, cholesterol dropped but people did not live longer. We also include the trials and reviews that found a benefit, so you see the full picture.
| Source | Type |
|---|---|
| Minnesota Coronary Experiment — recovered data (BMJ, 2016) Ramsden, Zamora, et al. · The BMJ · 2016 · A large 1968–73 double-blind trial in over 9,000 people, re-analyzed from recovered records. Swapping saturated fat for corn oil lowered cholesterol — yet the corn-oil group had no survival benefit and those who lowered cholesterol most had a higher risk of death. The single most-cited study in this debate. | STRONGEST FREE |
| Sydney Diet Heart Study — recovered data (BMJ, 2013) Ramsden, et al. · The BMJ · 2013 · 458 men who had already had a heart attack replaced saturated fat with safflower-oil linoleic acid. They had lower cholesterol but died at HIGHER rates from heart disease and all causes than the control group. A randomized trial, re-analyzed open-access. | STRONGEST FREE |
| Corn Oil in Treatment of Ischaemic Heart Disease (BMJ, 1965) Rose, Thomson, Williams · British Medical Journal · 1965 · One of the earliest trials of its kind: 80 men with heart disease split into control, olive oil, and corn oil groups. The corn-oil (linoleic acid) group fared the worst for repeat heart attacks and deaths — the authors called it "possibly harmful". | SUPPORTING FREE |
| Diet and Reinfarction Trial (DART) (The Lancet, 1989) Burr, Fehily, Gilbert, et al. · The Lancet · 1989 · Over 2,000 male heart-attack survivors advised to raise their polyunsaturated-to-saturated fat ratio saw no change in death rates — while separate advice to eat more oily fish lowered deaths. A clean null result for the seed-oil-style swap. | SUPPORTING FREE |
| Finnish Mental Hospital Study (Int. J. Epidemiology, 1979) Turpeinen, Karvonen, et al. · 1979 · Two hospitals swapped to a high-polyunsaturated diet, then swapped back years later. Heart-disease rates were about half as high on the polyunsaturated diet — included here as evidence FOR replacing saturated fat with linoleic acid. | OTHER SIDE FREE |
| PUFA in Place of Saturated Fat — meta-analysis (PLoS Medicine, 2010) Mozaffarian, Micha, Wallace · PLoS Medicine · 2010 · Pooled 8 randomized trials (13,000+ people). Replacing saturated fat with polyunsaturated fat was tied to 19% fewer heart-disease events — one of the main studies mainstream guidance relies on. Shown for balance. | OTHER SIDE FREE |
| Cutting saturated fat — Cochrane review, plain-language summary (2020) Hooper, et al. · Cochrane Database · 2020 · The most rigorous review body in medicine found that cutting saturated fat (often replacing it with linoleic acid) modestly reduced cardiovascular events but had little to no effect on overall risk of dying. A cautious, mixed verdict — shown for honesty. | OTHER SIDE FREE |
Why It Happens: The Mechanism
The "how": linoleic acid (the main fat in seed oils) is chemically unstable. In the body it oxidizes into reactive compounds (OXLAMs, 4-HNE) that damage cells, LDL, and mitochondria. These are the peer-reviewed papers behind that claim — most are fully open-access.
| Source | Type |
|---|---|
| Lowering dietary linoleic acid reduces oxidized metabolites in humans (2012) Ramsden, et al. · Prostaglandins Leukot. Essent. Fatty Acids · 2012 · A 12-week human trial: cutting linoleic acid intake significantly lowered blood levels of OXLAMs (the harmful oxidized breakdown products linked to pain and inflammation). Direct human proof that how much seed oil you eat controls these byproducts. | STRONGEST FREE |
| Oxidized linoleic acid metabolites damage liver mitochondria (2018) Schuster, et al. · Journal of Lipid Research · 2018 · Feeding mice the OXIDIZED metabolites of linoleic acid (not the plain fat) made liver mitochondria lose function and energy output and triggered cell death and inflammation — pinpointing the breakdown products as the damaging agents. | STRONGEST FREE |
| Lipid Peroxidation: how PUFA become toxic aldehydes (4-HNE, MDA) (2014) Ayala, Muñoz, Argüelles · Oxidative Med. & Cellular Longevity · 2014 · The core reference on the "4-HNE" mechanism: it walks through how omega-6 fats, once attacked by free radicals, break down into reactive aldehydes that damage proteins and DNA and are tied to heart disease, diabetes, cancer, and Alzheimer's. | STRONGEST FREE |
| Oxidation of mitochondrial cardiolipin (linoleic acid) in apoptosis (2014) Zhong, et al. · Redox Biology · 2014 · Cardiolipin, a fat found only in mitochondria, is normally built from four linoleic acid chains. This shows oxidation turns it into reactive, damaging byproducts (including 4-HNE) in real mitochondria during cell death and in atherosclerotic livers. | STRONGEST FREE |
| How oxidized LDL damages blood vessels (2022) Jiang, et al. · Frontiers in Cardiovascular Medicine · 2022 · Explains step-by-step how LDL — after its polyunsaturated fat (largely linoleic acid) is oxidized — injures the vessel lining, drives inflammation, and builds plaque, connecting fat oxidation to heart disease. | SUPPORTING FREE |
| Oxidized linoleic acid metabolites and pain signaling (2012) Ruparel, Green, Chen, Hargreaves · Molecular Pain · 2012 · OXLAMs directly switch on TRPV1, a nerve receptor that signals pain. Blocking them cut inflammatory pain sharply in animal models — a direct chemical link between oxidized seed-oil fat and pain. | SUPPORTING FREE |
| Linoleic acid — good or bad for the brain? (2020) Taha · npj Science of Food · 2020 · A fair-minded review: linoleic acid's oxidized metabolites appear to promote brain inflammation in animals, but the author is careful that firm human evidence is still limited. A good balanced overview rather than an alarmist one. | SUPPORTING FREE |
| Linoleic acid intake and chronic disease — narrative review (2023) DiNicolantonio, D'Adamo, et al. · Nutrients · 2023 · Pulls the OXLAM, cardiolipin, and mitochondrial threads into one narrative arguing excess linoleic acid contributes to chronic disease. A useful one-stop synthesis — treat it as an overview, not primary data. | OTHER SIDE FREE |
A Century of Rising Intake
How much seed oil people actually eat has exploded over the last hundred years — and it shows up measurably in human body fat. This is the exposure change at the heart of the concern.
| Source | Type |
|---|---|
| Changes in US omega-6 and omega-3 intake, 1909–1999 (2011) Blasbalg, Hibbeln, Ramsden, et al. · Am. J. Clinical Nutrition · 2011 · The landmark food-supply analysis: US soybean-oil consumption rose roughly 1000-fold over the century, pushing linoleic acid from about 2.8% to 7.2% of daily calories. The core "how it happened" citation. | STRONGEST FREE |
| Linoleic acid in US body fat rose 136% in 50 years (2015) Guyenet & Carlson · Advances in Nutrition · 2015 · Pooled 37 studies measuring linoleic acid directly in Americans' body fat from 1959 to 2008. It rose from about 9% to 21.5% of fat tissue — physical evidence in human tissue that the food-supply shift ended up in our bodies. | STRONGEST FREE |
| US soybean-oil production & consumption (USDA chart) USDA Economic Research Service · An official government chart showing decades of US soybean-oil production and consumption side by side — a hard-data view of how much has flowed into the food supply. | STRONGEST FREE |
| Seed Oils and Body Fatness Stephan Guyenet, Ph.D. · Whole Health Source · A neuroscientist charts the rise of linoleic acid in American body fat and calls the switch to seed oils "an uncontrolled experiment", while noting the health effects are still uncertain. Plain-language and free. | SUPPORTING FREE |
| Are seed oils healthful or harmful? (Harvard) Harvard T.H. Chan School of Public Health · 2024 · A mainstream public-health explainer of how seed oils became dominant, how they are processed, and why the omega-6 debate is still contested. A balanced counterpoint to the sources above. | OTHER SIDE FREE |
What Heat Does: Frying & Oxidation
Seed oils are least stable exactly where restaurants use them most — hot fryers, reused for hours. Heating them generates toxic aldehydes that end up in the food itself.
| Source | Type |
|---|---|
| Toxic aldehydes in cooking vegetable oils — review (2025) Sciano, et al. · Food Chemistry: X · 2025 · High-heat cooking breaks vegetable oils into toxic aldehydes (acrolein, formaldehyde, decadienal) that are highly reactive and can bond with proteins and DNA — linked to inflammation and cancer risk. Open-access. | STRONGEST FREE |
| Aldehydes from PUFA-rich oils in high-temperature frying (2022) Grootveld · Frontiers in Nutrition · 2022 · Argues polyunsaturated oils (corn, soybean, sunflower) generate substantial toxic aldehydes when fried, that these show up in the food and the kitchen air, and that current safety limits may understate the risk. | STRONGEST FREE |
| Toxic aldehydes get into fried food — real samples (Nature Sci. Reports, 2019) Moumtaz, Grootveld, et al. · Scientific Reports · 2019 · Tested real restaurant and fast-food fried food: polyunsaturated seed oils generated far more toxic aldehydes than a monounsaturated oil, and those aldehydes were detectable in the fried food itself. | STRONGEST FREE |
| Chemical changes in deep-fat frying — review (2025) Bazina, et al. · Food Science & Nutrition · 2025 · A comprehensive open-access review of frying chemistry — oxidation, hydrolysis, polymerization — and how heat and repeated use build up trans fats and breakdown compounds linked to cardiovascular harm. | SUPPORTING FREE |
| Repeated heating raises trans fat, drops PUFA — measured (2022) Szabó, et al. · Foods · 2022 · Heated common oils repeatedly at normal frying temperature and measured the fats: polyunsaturated content fell and trans-fat content rose with repeated heating — the reused-fryer-oil worst case, quantified. | SUPPORTING FREE |
Metabolism, Weight & Insulin
Animal and human studies on what linoleic acid does to body fat, appetite, and insulin. The animal evidence here is striking; the human picture is still being worked out.
| Source | Type |
|---|---|
| Soybean oil more obesogenic than coconut oil or fructose in mice (2015) Deol, Sladek, et al. (UC Riverside) · PLOS ONE · 2015 · At identical calories, the soybean-oil (high linoleic acid) diet caused the most weight gain, fatty liver, diabetes, and insulin resistance of any group — including more than the high-fructose diet. The study that put seed-oil obesity research on the map. | STRONGEST FREE |
| Dietary linoleic acid raises "munchies" signals and induces obesity (2012) Alvheim, et al. · Obesity · 2012 · Mice fed diets mimicking rising 20th-century American linoleic acid intake tripled their endocannabinoids (the body's appetite/fat-storage "munchies" molecules) and became obese — a proposed mechanism for how seed oils drive overeating. | STRONGEST FREE |
| Oxylipins tie soybean oil to obesity in mice (2017) Yang, Deol, et al. · Scientific Reports · 2017 · A follow-up comparing regular soybean oil to a low-linoleic-acid version found the inflammatory breakdown products of linoleic acid tracked weight gain — a specific chemical mechanism, not just calories. | SUPPORTING FREE |
| Changing how mice process linoleic acid blocks the weight gain (2025) Deol, Sladek, et al. · Journal of Lipid Research · 2025 · The newest UC Riverside paper: mice engineered to metabolize linoleic acid differently gained far less weight on the same soybean-oil diet and avoided fatty liver — further confirming the breakdown products as an obesity driver. | SUPPORTING FREE |
| Overfeeding sunflower vs palm oil in humans — LIPOGAIN (2014) Rosqvist, et al.; commentary by Bray & Krauss · Diabetes · 2014 · A human trial overfeeding equal-calorie muffins made with sunflower oil or palm oil for 7 weeks. Notably, the saturated palm oil caused MORE liver and belly fat than the linoleic-acid oil — a result that complicates the simple "seed oil = fat" story. Included for honesty. | OTHER SIDE FREE |
Eyes, Head, Liver & Skin
Research tying linoleic acid to specific organs — from Chris Knobbe's macular-degeneration hypothesis to randomized migraine trials, fatty liver, and skin.
| Source | Type |
|---|---|
| Lowering linoleic acid cut migraine days — randomized trial (BMJ, 2021) Ramsden, et al. · The BMJ · 2021 · A 182-person, 16-week randomized trial: raising omega-3 while LOWERING linoleic acid (seed oils) robustly reduced migraine frequency, severity, and headache hours versus a typical American-diet control. Rare, strong human trial evidence. | STRONGEST FREE |
| Diet change for chronic headaches — randomized trial (Pain, 2013) Ramsden, Faurot, et al. · Pain · 2013 · Chronic-headache patients who both raised omega-3 and lowered linoleic acid had significantly fewer, less severe headache days than those who only lowered linoleic acid — a measurable pain benefit from cutting seed oils. | STRONGEST FREE |
| Seed oils as the proposed cause of macular degeneration (2017) Knobbe & Stojanoska · Medical Hypotheses · 2017 · Ophthalmologist Chris Knobbe's landmark hypothesis: across 25 nations, macular degeneration was rare before industrial seed oils and rose 30–40 years after their intake climbed. The full abstract laying out the argument is free on PubMed. | OTHER SIDE FREE |
| Fatty acids and macular degeneration — review (Cells, 2025) Bisen & Singh · Cells · 2025 · A recent review finds omega-3 fats appear protective for the eyes while higher omega-6 (linoleic acid) intake is linked to more of the severe "wet" form of macular degeneration — an independent, fully-free confirmation of the eye link. | SUPPORTING FREE |
| Bioactive fatty acids in fatty liver disease (NAFLD) — review (2016) Juárez-Hernández, et al. · Nutrition Journal · 2016 · Explains how a high ratio of omega-6 (linoleic acid) to omega-3 is tied to fat buildup, inflammation, and damage in non-alcoholic fatty liver disease, one of the fastest-growing liver conditions worldwide. | SUPPORTING FREE |
| Oxidized linoleic acid as a marker of liver injury (2013) Santoro, Caprio, Feldstein · Clinical Lipidology · 2013 · The oxidized byproducts of linoleic acid (9- and 13-HODE) run higher in patients with the more damaging form of fatty liver (NASH), and lowering dietary linoleic acid reduces these byproducts in humans. | SUPPORTING FREE |
| Linoleic acid in skin and hair health — review (2025) Wang, Jia, He · Int. J. Molecular Sciences · 2025 · Linoleic acid is needed for a healthy skin barrier, but this review also notes that abnormal linoleic acid metabolism is linked to acne and eczema — tying imbalanced omega-6 to common inflammatory skin conditions. | SUPPORTING FREE |
The Population Evidence and the Other Side
Honesty matters. Most large observational studies that measure linoleic acid in the body (not just what people say they eat) find it neutral or even protective for heart disease and diabetes. Observational studies show association, not cause — but a page that hid them would not be worth citing. Read them alongside the trials and mechanism above and decide for yourself.
| Source | Type |
|---|---|
| Blood omega-6 and cardiovascular disease — 30-cohort pooled analysis (2019) Marklund, Wu, et al. (global consortium) · Circulation · 2019 · Measured actual linoleic acid in the blood of ~70,000 people across 13 countries. Higher levels were linked to LOWER cardiovascular death and stroke — one of the largest, most rigorous studies, and it points away from harm. | OTHER SIDE FREE |
| Dietary linoleic acid and heart disease — 13-cohort meta-analysis (2014) Farvid, et al. · Circulation · 2014 · 310,000+ people: those eating the most linoleic acid had 15% fewer heart-disease events and 21% fewer heart-disease deaths than those eating the least. Major evidence that intake is not harmful to the heart. | OTHER SIDE FREE |
| Blood omega-6 and type 2 diabetes — 20-cohort analysis (2017) Wu, Marklund, et al. · Lancet Diabetes & Endocrinology · 2017 · Across 20 cohorts, people with more linoleic acid in their blood were LESS likely to develop type 2 diabetes. The authors read it as support for a protective role. | OTHER SIDE FREE |
| Specific dietary fats and mortality — 126,000 people (2016) Wang, Hu, et al. · JAMA Internal Medicine · 2016 · Over up to 32 years, higher linoleic acid intake was linked to lower total mortality, and replacing saturated fat with it to a 27% lower death rate. A large, long cohort that points away from harm. | OTHER SIDE FREE |
| Linoleic acid in body fat and stroke — Danish study (2018) Venø, et al. · J. American Heart Association · 2018 · Biopsied body fat from 57,000+ Danish adults: more stored linoleic acid was linked to a LOWER rate of ischemic stroke — a direct tissue-measurement study arguing against a linoleic-acid/stroke link. | OTHER SIDE FREE |
The Doctors & Researchers
Clinicians and independent researchers who argue industrial seed oils are a primary driver of modern chronic disease. Each keeps a free public library.
| Source | Type |
|---|---|
| Chris Knobbe, MD — Cure AMD Foundation Ophthalmologist, UT Southwestern (emeritus) · Argues seed oils are the unifying driver of macular degeneration and other chronic disease. Free articles, lecture videos, and a free book chapter. | FREE |
| Cate Shanahan, MD — the "Hateful Eight" oils Biochemist & family physician, author of "Dark Calories" · Coined the "Hateful Eight" seed oils and explains how their oxidation damages cells. Free articles, guides, and an 8-day challenge. | FREE |
| Nina Teicholz — The Nutrition Coalition Investigative science journalist · Documented how the evidence for replacing animal fat with vegetable oils was far weaker than the public was told. Free reports and reporting. | FREE |
| Tucker Goodrich — the mechanistic case Independent researcher · A former "seed oil zealot" turned critic; deep, heavily-sourced essays on linoleic acid, oxidation, heart disease, and obesity. Free to read. | FREE |
| The Weston A. Price Foundation Nonprofit nutrition foundation · A large free archive of articles on traditional fats vs. industrial seed oils, with citations throughout. | FREE |
| Paul Saladino, MD Physician, animal-based advocate · Argues seed oils and processed foods drive chronic disease. Free newsletter and podcast. (Some of his broader claims have drawn scientific pushback — read critically.) | FREE |
| Georgi Dinkov ("Haidut") Researcher, IdeaLabs · A leading continuer of Ray Peat's bioenergetic, anti-PUFA framework, applying it to current research. Free articles. | FREE |
| Stephan Guyenet, Ph.D. Neuroscientist & obesity researcher · Co-documented the real-world rise of linoleic acid in Americans' body fat — data widely cited by seed-oil researchers — while staying cautious about firm causal claims. Free articles. | FREE |
Books
Deeper reads. The books themselves are paid, but each links to a free overview, excerpt, or interview so you can judge before buying.
| Source | Type |
|---|---|
| Dark Calories Cate Shanahan, MD · Argues oxidative damage from seed oils — not cholesterol — is the root of most chronic disease. Free overview and excerpts on her site. | BOOK |
| Deep Nutrition Cate Shanahan, MD · Makes the case that traditional, unprocessed fats — not seed oils — shaped healthy human genetics. Free key-principles summary on her site. | BOOK |
| The Big Fat Surprise Nina Teicholz · Investigative history of how US guidelines pushed people toward vegetable oils. Learn about it free via her nonprofit (nutritioncoalition.us); the book is paid. | BOOK |
| Ancestral Dietary Strategy to Prevent & Treat Macular Degeneration Chris Knobbe, MD · The diet-and-disease case for seed oils driving macular degeneration. Free Chapter 1 via the Cure AMD site; author takes no royalties (proceeds fund the charity). | BOOK |
Watch & Listen (free)
Prefer video or audio? These are all free to stream.
| Source | Type |
|---|---|
| Diseases of Civilization — the seed-oil lecture Chris Knobbe, MD · The signature hour-long talk laying out the historical and epidemiological case that seed oils drive the modern "diseases of civilization". Free on YouTube. | FREE |
| Fed A Lie — full documentary Featuring Saladino, Knobbe, Teicholz · A feature-length documentary tracing how seed oils entered the food supply and the case that they drive obesity and chronic disease. Free, full film on YouTube. | FREE |
| How Vegetable Oils Destroy Our Health — podcast Chris Knobbe, MD · Wise Traditions Ep. 425 · A free podcast episode on when and how seed oils entered the food supply and the biochemical case against them. | FREE |
| The Truth About Dark Calories Cate Shanahan, MD · Shanahan explains her "energy model" of insulin resistance and how seed oils make body fat dysfunctional. Free on YouTube. | FREE |
| Joe Rogan Experience #1058 — Nina Teicholz Long-form interview · A long conversation on how US dietary guidelines pushed Americans toward vegetable oils and away from saturated fat. Free to stream on Spotify. | FREE |
The short version
Seed oils (soybean, canola, corn, sunflower, safflower, cottonseed) are very high in linoleic acid — an unstable polyunsaturated fat that oxidizes easily, inside the body and out. The trial, mechanism, and animal evidence above argue that flooding the modern diet with it drives chronic disease; the population studies are more reassuring. Traditional fats — beef tallow, butter, olive oil — don't carry the same oxidation risk. Everything here is gathered in one place so you can check it yourself.