Are Seed Oils Actually Unhealthy? What the Evidence Really Says

Surf Ready Fitness
Dec 2
3 min read

Every few years, nutrition needs a new villain.

First it was fat. Then carbs. Then fat again. And now the latest dietary bad guy getting dragged through the mud is… seed oils cue dramatic music.

“Seed oils” typically refer to vegetable oils such as sunflower, soybean, canola, corn, and grapeseed oil—all of which are rich in polyunsaturated fatty acids (PUFAs). If you’ve spent more than 10 minutes on social media, you’ve likely heard that these oils are “toxic,” cause inflammation, wreck your mitochondria, and are responsible for practically every chronic disease on earth.

But what actually happens when we look at real data instead of memes?

Spoiler: this isn’t the nutritional apocalypse some are claiming.

What the Research Reviewed

A 2023 umbrella review published in Advances in Nutrition examined 48 systematic reviews and meta-analyses evaluating the effects of vegetable oils on health outcomes including:

Blood lipids
Blood pressure
Blood sugar
Body weight
Cardiovascular disease
Cancer
Inflammation

Citation:

Tørris C, Småstuen MC. Health Effects of Vegetable Oils: An Umbrella Review. Advances in Nutrition. 2023; nmac085. https://doi.org/10.1016/j.advnut.2023.100222

This is one of the most comprehensive analyses to date, meaning it didn’t just look at a single study—it looked at the studies of the studies.

What They Found (It’s Not What TikTok Says)

1. Lipids: Seed Oils Tend to Improve Cholesterol, Not Worsen It

Oils high in mono- and polyunsaturated fats generally improved or at least maintained healthy lipid profiles when compared to more saturated fats.

Highlights:

Canola oil → lowered total cholesterol and LDL; neutral effect on triglycerides/VLDL
Rice bran oil → lowered total cholesterol and LDL
Olive oil → lowered total cholesterol, sometimes LDL, and often raised HDL
Coconut & palm oils → consistently raised LDL and total cholesterol, though they also raised HDL

So the idea that seed oils “wreck your cholesterol” doesn’t line up with what the evidence shows.

2. Blood Pressure & Blood Sugar: Small but Positive Effects

A few oils showed beneficial effects on cardiometabolic markers:

Flaxseed oil → small but meaningful reductions in blood pressure (likely due to ALA)
Sesame oil → modest reductions in BP and improvements in fasting glucose & HbA1c
Olive oil (and occasionally coconut oil) → slight improvements in blood sugar markers

Again, not exactly the toxic sludge narrative.

3. Inflammation, Heart Disease & Cancer: No Evidence of Increased Risk

Across the reviews analyzed:

No increase in inflammatory markers
No convincing link to higher cardiovascular event risk
No evidence of increased cancer risk

These are the very claims often repeated online—yet the data simply doesn’t support them.

4. Body Weight & Composition: No Meaningful Impact

A few studies found tiny changes in body weight or body composition, but nothing large enough to matter clinically.

Important Caveats (Because Context Matters)

Before anyone runs out and chugs a bottle of canola oil, a few notes:

The overall certainty of evidence was generally low (nutrition science is messy).
Oils aren’t consumed in isolation—they’re part of dietary patterns.
Home cooking oils ≠ industrial fryers that repeatedly reheat oil (a very different chemical environment).
Seed oils in the context of ultra-processed food diets are not the same as seed oils used in normal home cooking.