Are Seed Oils Bad For Your Heart Or Health?

Seed oils are cardioprotective. Period.

Let’s take this head on.

Nearly every Medfluencer who is on social media keeps talking about seed oils and vegetable oils. They are referring to oils that are derived from seeds like safflower, sunflower, peanut, canola, and many others. These oils are high in omega 6 fatty acids, specifically linoleic acid.

Medfluencers try to scare the public into avoiding seed oils and instead, buy their supplements. They cite one rat study from 1965. Which is absurd given the amount of human data we have on seed oils.

Or they cite many of the studies mentioned in other parts of this book on saturated fat versus unsaturated fats.

Let’s be clear…

Rats are not humans.

Petri dishes are not human.

Test tubes are not human.

We do not need to use rat studies and petri dish studies when we have actual human outcome studies. They often cite some very flawed small studies that we have already discussed.

But first let’s look at the human outcomes studies on seed oils that show benefit.

Multiple studies now show that “Seed Oils” (Linoleic acid, LA, and AA) reduce CVD.

Perhaps the most comprehensive was published in Circulation. Circulation is one of the most respected peer reviewed journals. It’s very difficult to get past their editorial board and publish your work. Trust me, I’ve done research in a lab, and I know.

The study looked at over 68k participants for 31.9 years of follow up and the endpoints were reached over 15k times. They had 76k tissue biopsies to make sure the linoleic acid group was actually consuming linoleic acid (seed oils). They looked at blood and adipose tissue samples to confirm consumption of linoleic acid. You can’t really beat the design.

You can read it here:
https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.118.038908 

Results from the study verbatim:
“In 30 prospective studies with medians of follow-up ranging 2.5 to 31.9 years, 15,198 incident cardiovascular events occurred among 68,659 participants. Higher levels of LA were significantly associated with lower risks of total CVD, cardiovascular mortality, and ischemic stroke, with hazard ratios per interquintile range of 0.93 (95% CI, 0.88–0.99), 0.78 (0.70–0.85), and 0.88 (0.79–0.98), respectively, and nonsignificantly with lower coronary heart disease risk (0.94; 0.88–1.00). Relationships were similar for LA evaluated across quintiles. AA levels were not associated with higher risk of cardiovascular outcomes; in a comparison of extreme quintiles, higher levels were associated with lower risk of total CVD (0.92; 0.86–0.99). No consistent heterogeneity by population subgroups was identified in the observed relationships.

Conclusions:
In pooled global analyses, higher in vivo circulating and tissue levels of LA and possibly AA were associated with lower risk of major cardiovascular events. These results support a favorable role for LA in CVD prevention.”

That’s definitive and overwhelming evidence. There are no human outcome trials that show harm from seed oil.

Read that again.

There isn’t a single human outcome trial that shows harm from seed oils.

Not one.

In fact, there are many trials that show benefit. It’s not news. We have always known that MUFAs and PUFAs are cardioprotective. It’s an overwhelming amount of evidence. Nearly every study that has been done has shown that MUFA and PUFA are beneficial.

What About Butter For Seed Oil Substitution Studies?

This is especially true when substituting saturated fat (butter) for a PUFA. The benefits are undeniable.

Let’s examine some of these studies.

One study found that soybean oil lowers circulating cholesterol levels and coronary heart disease risk and has no effect on markers of inflammation and oxidation. You can read it:
https://pubmed.ncbi.nlm.nih.gov/34171740/ 

Another study found that when you substitute saturated fat for poly unsaturated fat that you improve flow mediated dilation and reduce inflammation. In this study, a high saturated fat diet increased inflammation and flow-mediated dilation compared to high PUFAs, MUFAs, and or a high-carbohydrate diet. We have discussed some of this in parts of the book discussing saturated fat.
Study:
https://pubmed.ncbi.nlm.nih.gov/15774905/ 

Another study found that substituting saturated fat for seed oils (rapeseed and sunflower) in a 1 to 1 ratio (isocaloric) showed a 5-7% reduction in LDL-C, apoB, and total cholesterol.
Study:
https://pubmed.ncbi.nlm.nih.gov/8194494/ 

Another study demonstrated that replacing saturated fat with PUFAs or carbohydrates was associated with a reduction in cardiovascular disease in adults with type 2 diabetes. Yes, those with insulin resistance did better on seed oils. After 9.8 years of follow up, there was a 13% reduction in heart disease for only a 2% replacement of saturated fat for PUFAs and 18% for a 5% replacement with carbohydrates. Those with higher levels of seed oil intake actually had a 25% relative risk reduction in CVD.
Study:
https://pubmed.ncbi.nlm.nih.gov/33611616/ 

Another large study published in Circulation showed that linoleic acid (LA) consumption was inversely correlated with CVD. When the highest category was compared with the lowest category, dietary LA was associated with a 15% lower risk of CV events and 21% reduction in CV deaths. A 5% of energy increment in LA intake replacing energy from saturated fat intake was associated with a 9% lower risk of CV events and a 13% reduction in CV deaths.
Study:
https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.114.010236 

They have also done crossover studies with saturated fat, MUFAs, and PUFAs. ApoB and LDL-C levels both dropped on the PUFA diet. At the end of the study, the authors concluded that the most important risk factor modification is to reduce saturated fat intake,
Study:
https://pubmed.ncbi.nlm.nih.gov/8199179/ 

Another study examined the metabolic effects of saturated fats versus seed oils (PUFAs) in ketogenic diets. They found that a ketogenic diet where they substituted saturated fat for PUFA actually induced better ketosis without raising total cholesterol or LDL-C. PUFA also improved insulin sensitivity.
Study:
https://pubmed.ncbi.nlm.nih.gov/15070924/ 

Studies have also found that seed oils improved insulin sensitivity. In one study the authors found that, “The evidence suggests that replacing saturated fats and trans fatty acids with unsaturated (polyunsaturated and/or monounsaturated) fats has beneficial effects on insulin sensitivity and is likely to reduce risk of type 2 diabetes. Among polyunsaturated fats, linoleic acid from the n-6 series improves insulin sensitivity”.
Studies:
https://pubmed.ncbi.nlm.nih.gov/19032965/ 
https://pubmed.ncbi.nlm.nih.gov/27434027/ 

What About Non Alcoholic Fatty Liver Disease NAFLD And Seed Oils?

As we have discussed in other sections, PUFAs reduce liver fat significantly when replacing saturated fats.
Study:
https://pubmed.ncbi.nlm.nih.gov/31369090/ 

Do Seed Oils Cause Weight Gain?

In an interesting plot twist, there was a study that found that people who added seed oils during the holiday season were less likely to gain weight and maintained that benefit for 6 months.
Read the study here:
https://pubmed.ncbi.nlm.nih.gov/16924272/ 

Another study found that consuming seed oil (sunflower) reduced body fat in those with obesity. They consumed 500 calories from sunflower seed oil for 12 weeks and had reductions in body weight, adipose tissue, adipogenesis, and waist circumference.
Study:
https://www.sciencedirect.com/science/article/abs/pii/S0271531723001240 

Another study also found that supplementing with seed oil reduced body fat mass and increased lean body mass in overweight and obese adults.
https://pubmed.ncbi.nlm.nih.gov/17313718/ 

Are Seed Oils Healthier Than Olive Oil?

Another meta-analysis from November 2023 found that canola oil reduced LDL-C more than olive oil. Canola oil reduced LDL-C by 6.13 mg/dL (weighted mean difference) compared to olive oil.
Study:
https://pubmed.ncbi.nlm.nih.gov/35866510/ 

A meta-regression analysis by Mensink found that isocaloric substitutions of carbohydrates for oleic acid (the main fatty acid found in olive, pecan, canola, peanut, macadamia, sunflower, and grapeseed oil) decreased LDL-C, HDL-C, and triglycerides substantially.
Study:
https://pubmed.ncbi.nlm.nih.gov/1386252/ 

Do Seed Oils Cause Cancer?

Seed oils do not increase the risk of cancer and may even reduce the risk of cancer.
Studies:
https://pubmed.ncbi.nlm.nih.gov/32114592/ 
https://pubmed.ncbi.nlm.nih.gov/32723506/ 
https://pubmed.ncbi.nlm.nih.gov/9665108/