Are Seed Oils Bad for You?
Are Seed Oils Bad for You? What Happened When Two Patients Cut Them
No. The evidence runs the other way, and I can show you what the swap does on a lab report because I see it most weeks now.
Linoleic acid is the main polyunsaturated fat in soybean and conventional sunflower oil, and part of what is in canola. People with more of it in their blood and fat tissue have less cardiovascular disease, not more. Randomized trials have looked for the inflammation everyone talks about and have not found it. What moves risk is what people cook with once they quit: butter, tallow, ghee, coconut oil. More saturated fat than before, which is the one dietary change here with decades of trial data behind it, all pointing the wrong way.
I practice endocrinology in the western suburbs of Chicago. Two patients from the last year, details changed.
The patient who is probably you
She was 49. Perimenopausal, sleeping badly, and frustrated that the ten pounds she had gained since 45 would not move. She had cleaned up her diet the way her feed told her to. Seed oils were the first thing to go. She cooked in butter and ghee, bought the tallow-fried chips, and read labels for "canola" the way she used to read them for sugar.
Her PCP had told her the year before that her cholesterol was "a little high, let's watch it." She came to me because her repeat labs were higher and she wanted to know why, since she was eating better than she ever had. Fourteen months of clean eating had taken her LDL from 132 to 154, and her ApoB, which nobody had checked before, was 112.
Twelve weeks after we put olive oil and canola back in the pan and moved ghee to the dishes that call for it, her LDL was back to 134. Nothing else in her life changed in those twelve weeks. She was not eating worse. She had been told, by people who sounded certain, that the thing raising her LDL was the thing lowering it.
The patient who did everything the podcast said
He was 47 and came in for a second opinion on his "optimization labs." A year on a longevity-podcast protocol: seed oils out, tallow and butter in, four days a week in the gym, a supplement stack from the same clinic that ran the labs. He felt fine. He wanted to know why his numbers did not match how hard he was working.
His LDL had gone from 118 to 147. Same fix, olive oil and canola back in, and twelve weeks later it was 123. He had read more than most of my patients. The advice sounded rigorous and came with its own lab panel, and that is why it worked on him.
Both patients, side by side:
| A year earlier | After the swap | 12 weeks after switching back | |
|---|---|---|---|
| Patient A, 49F | |||
| LDL cholesterol | 132 mg/dL | 154 mg/dL | 134 mg/dL |
| ApoB | not checked | 112 mg/dL | 94 mg/dL |
| Triglycerides | 110 mg/dL | 121 mg/dL | 104 mg/dL |
| Patient B, 47M | |||
| LDL cholesterol | 118 mg/dL | 147 mg/dL | 123 mg/dL |
| ApoB | not checked | 109 mg/dL | 89 mg/dL |
| Patient details changed to protect privacy. | |||
What the evidence on seed oils says
The case against seed oils comes down to one claim with data attached: linoleic acid, an omega-6 fat, drives inflammation and heart disease. The processing argument, hexane extraction and high-heat refining, is real as a description of how commodity oils are made, but it has never been shown to change what those oils do to people. The outcome data below were collected on the same refined oils sold in grocery stores. So the claim that matters has been tested.
Johnson and Fritsche reviewed 15 randomized trials that changed how much linoleic acid healthy adults ate and then measured inflammatory markers (Journal of the Academy of Nutrition and Dietetics, 2012). Virtually no evidence that more linoleic acid raised any of them. A larger meta-analysis of 30 randomized trials reached the same conclusion (Su et al., Food & Function, 2017). That is intervention data, the kind the inflammation claim would need and does not have.
Marklund and colleagues pooled 30 cohorts, 68,659 people, and measured linoleic acid in blood and fat tissue rather than food diaries (Circulation, 2019). Higher levels went with lower total cardiovascular disease, lower cardiovascular death, and lower ischemic stroke. This is association data and cannot prove cause. It tells you which way the signal points.
The 2020 Cochrane review pooled 15 randomized trials of cutting saturated fat, about 56,000 people (Hooper et al.). Combined cardiovascular events fell 17%. Replacing saturated fat with polyunsaturated fat or carbohydrate appeared useful; the data on other replacements were too thin to say. Both of my patients ran that trial backwards.
One honest qualifier. A risk-stratified review published this past December (Steen et al., Annals of Internal Medicine) found that the absolute benefit of cutting saturated fat over five years is concentrated in people already at high cardiovascular risk, and that the effect was largest when polyunsaturated fat did the replacing. For a healthy 49-year-old, the payoff in heart attacks avoided is smaller than the headline number. The LDL effect is not smaller. It is what you see in the table, and LDL exposure compounds over decades.
The 2026 ACC/AHA dyslipidemia guideline, published this April, makes the swap a Class 1 recommendation: replace saturated and trans fat with monounsaturated and polyunsaturated fat to lower LDL and cardiovascular risk (Blumenthal et al., Circulation, 2026). It names the sources. Saturated: red meat, butter, high-fat milk, coconut oil, palm oil. Polyunsaturated: fish, nuts, flax, chia, and corn, sunflower, and soybean oil. The oils the internet says to throw out are on the guideline's list of what to eat instead.
The one study they will cite back at you
The Minnesota Coronary Experiment. Ramsden and colleagues recovered data from that 1968 to 1973 trial, in which a corn oil diet lowered cholesterol by about 14% without lowering mortality (BMJ, 2016). It deserves a read. It also ran in six state mental hospitals and one nursing home, and about three quarters of the participants were on the diet for under a year. Against one old trial with those problems sits the pooled randomized outcome evidence in Cochrane and a current Class 1 guideline recommendation. That is the whole argument.
None of this makes seed oils a health food. Fried food is still fried food. The fat with the best randomized outcome evidence is olive oil inside a Mediterranean pattern (PREDIMED, NEJM 2018, about 30% fewer major cardiovascular events than a low-fat control in high-risk adults), though that trial tested the whole diet, not the oil alone.
A note for my South Asian patients
Ghee at home because that is what your mother used. I know. Ghee is the cultural default, and South Asians carry higher cardiometabolic risk at a lower BMI than the standard charts assume. The American Diabetes Association lowers the BMI threshold for risk-based diabetes screening in Asian American adults from 25 to 23 for exactly that reason (Hsu et al., Diabetes Care, 2015). Adding saturated fat on top of that baseline because an influencer told you seed oils were poison is not a neutral choice. Keep the ghee for the dishes that need it. Do not make it the default fat.
If you have already made the swap
Get an LDL and an ApoB. If you cut seed oils in the last year and replaced them with butter, tallow, ghee, or coconut oil, put the numbers next to your last draw from before the change. That settles it faster than anything you read online.
On fats: olive oil as the default, canola or avocado oil when you need heat. Fatty fish twice a week covers omega-3, and that is what the guideline recommends. A fish oil capsule does not lower cholesterol; the same 2026 guideline gives supplements a Class 3, no benefit, and names fish oil. If you are not eating fish, and most of my patients are not, a third-party tested EPA/DHA stands in for the fish you did not eat. That is the only claim I make for it. The one I use is in my Fullscript dispensary. The two oils I keep at home are a good extra virgin olive oil and avocado oil for the pan.
If your cholesterol went up after you cleaned up your diet, I am happy to look at the numbers with you. Book a consult here.
References
I use AI to help draft posts like this one. Every clinical claim and citation is checked and verified by me before it goes up.
