Are the Seed Oil Trials Confounded by Trans Fats?
Part 1: The LA Veterans Administration Hospital Study
The randomized controlled trials of seed oils done in the mid-20th century in net showed that seed oils are not good at preventing heart disease and probably raise the risk of cancer.
The idea behind these trials was that the polyunsaturated fatty acids (PUFAs) in seed oils will lower cholesterol levels in the blood and thereby prevent heart disease.
Detractors from this idea focus on PUFAs making our tissues highly vulnerable to oxidative damage — very similar to the rust that accumulates on metal objects kept outdoors over time — and maintain that these fats could worsen the risk of heart disease by making the lipoproteins that carry cholesterol in the blood, such as LDL, more vulnerable to oxidative damage.
The failure of the seed oil trials to show a convincing reduction in heart disease and their worrisome finding that they may increase the risk of cancer suggests that this vulnerability to tissue damage is the mechanism that wins out in the long run.
One of the criticisms of these trials is that they are confounded by the use of trans fats in the seed oil groups.
While there are some trans fatty acids that occur in nature, such as in beef or dairy fat, there are specific trans fatty acids that occur in massive amounts in partially hydrogenated vegetable oils that do not occur in nature.
Hydrogenation itself is done to make liquid oils harder. When carried to completion, it turns all of the monounsaturated and polyunsaturated fatty acids to saturated fatty acids.
However, the path from a polyunsaturated fatty acid to a saturated fatty acid involves a monounsaturated fatty acid as an intermediate.
The definitional chemical characteristic of a saturated fatty acid is that it contains only single bonds and no double bonds, whereas monounsaturated fatty acids contain one double bond and polyunsaturated fatty acids contain more than one. The path from a natural double bond found in an unsaturated fatty acid to the single bond of a saturated fatty acid involves the formation of an unnatural trans double bond.
Thus, partial hydrogenation causes a loss of PUFA, but an increase in both monounsaturated and saturated fats, and the unique production of unnatural trans fats that are not found in any other foods.
Partially hydrogenated oils have been effectively banned in the United States and various other countries, but were widespread during the time of the classic seed oil trials.
Were these trials truly confounded by these unnatural trans fats?
We start our analysis with the longest seed oil trial ever conducted, the eight-year LA Veterans Administration Hospital Study.
The claim that it is confounded by trans fats relates to the use of a margarine in the seed oil group. There were actually two margarines used, one which was free of trans fats and one which contained trans fats. Here, we dig into historical sources such as advertising materials, preserved boxes with ingredient labels, patent infringement lawsuits, and scientific papers of the era. We blend this with direct analyses of the margarines and foods made with them and physiological biomarkers of trans fat consumption to narrow in on the best answer.
But first, why was this trial so incredibly important?
Read the full article here:
https://chrismasterjohnphd.substack.com/p/are-the-seed-oil-trials-confounded
February 5, 2026 951 4
