Quick Study Analysis: Sarah Berry on Seed Oils

tl;dr: This has been on my to-do list, Dr. Harcombe got to it first.

Zoë Harcombe has been a warrior for dietary sanity for a long time, mostly on the LCHF and heart disease fronts.

Today she takes a look at the problems with seed oil advocacy. I’ve had an eye on Sarah Berry (no Dr. honorific there, she hasn’t earned it from me) for a while, as she seems to be a ripe target for a debunk.

“ZOE & misinformation about seed oils”

She’s taken this article from behind her paywall, please read the whole thing. (ZOE is the name of the company for which Berry works, and has no relation to Dr. Harcombe.)

I think the most extravagant piece of misinformation Berry attempts to spread in this interview is the following, which Dr. Harcombe doesn’t note:

“And these terms that you might hear that are used as processing techniques are things like bleaching and deodorization. Now they do sound quite scary. People are thinking probably bleaching, peroxide. It's not as scary as it sounds. What happens is, is the end oil is therefore very stable. There are no harmful chemicals left in that end-stage oil.” (Harcombe, 2025)

This is either a lie, or disqualifying. By disqualifying, I mean that it’s so wrong that if she’s not aware of it she’s grossly negligent in a professional capacity.

Even refined seed oils contain high levels of “harmful chemicals” such as lipid peroxides, and as this paper (Farhoosh, 2009) makes clear, the oils are rancid before they are processed, and are still rancid and likely to become more so afterward. They are not stable.

(Farhoosh, 2009)

“The results obtained in this study indicated that: (a) among the commercial refining steps, the neutralisation step had the highest effect on the TPC content and polar compounds’ distribution, did not markedly change the content of the primary (PV) and secondary (CV) products of lipid oxidation, and effectively decreased the oxidative stability of the oils, due to the almost complete removal of the indigenous phenolic compounds; (b) the content of carbonyl compounds, which are considered to be one of the most important secondary oxidation products influencing the sensory properties of edible oils, was a function of the fatty acid composition and the initial quality of the oils, and continuously increased during the commercial refining steps;…” (Farhoosh, 2009)

Lipid oxidation = rancidity.

“The Effect of Commercial Refining Steps on the Rancidity Measures of Soybean and Canola Oils” (Farhoosh, 2009)

Someone should take Berry’s PhD back.

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References

Farhoosh, R., Einafshar, S., & Sharayei, P. (2009). The Effect of Commercial Refining Steps on the Rancidity Measures of Soybean and Canola Oils. Food Chemistry, 115(3), 933–938. https://doi.org/10.1016/j.foodchem.2009.01.035

Harcombe, Z. (2025, February 3). ZOE & misinformation about seed oils [Newsletter]. Dr. Zoë Harcombe Ph.D. https://www.zoeharcombe.com/2025/02/zoe-misinformation-about-seed-oils/