I thought I would revisit the idea of trans fatty acids because the late Fred Kummerow got an honourable mention on twitter recently. He is largely responsible for the removal of industrial trans fatty acids from the food chain. No one would argue that that was not a Good Thing.
Back in the 1970s a study was completed which applied a diet from which saturated fats were largely removed and linoleic acid, mostly from corn oil, was increased to about 13% of calories. In a "control" diet saturated fats were as unchanged as practical and linoleic acid limited to just under 5% of calories. That should be a pretty good test of the miraculous benefits of dietary PUFA for blood cholesterol lowering.
However the "control" diet just happened to be specifically increased in industrial trans fatty acids from commercial margarine (1960s style USA margarine), though no one knows by how much, ie there was no genuine "control" diet.
This is what the diets looked like
Cholesterol lowering diet:
"Liquid corn oil was used in place of the usual hospital cooking fats (including hydrogenated oils) and was also added to numerous food items (for example, salad dressings, filled beef (lean ground beef with added oil), filled milk, and filled cheeses). Soft corn oil polyunsaturated margarine was used in place of butter. This intervention produced a mean reduction in dietary saturated fat by about 50% (from 18.5% to 9.2% of calories) and increased linoleic acid intake by more than 280% (from about 3.4% to 13.2% of calories)".
"It was designed to appear similar to the experimental diet. Notably, free surplus USDA food commodities including common margarines and shortenings were key components of the control diet, making the daily per participant allocation from the state of Minnesota adequate to cover the full costs. As common margarines and shortenings of this period were rich sources of industrially produced trans fatty acids, the control diet contained substantial quantities of trans fat. Compared with the pre-randomization hospital diet, the control diet did not change saturated fat intake but did substantially increase linoleic acid intake (by about 38%, from 3.4% to 4.7% of calories)".
You have to wonder about the inclusion of trans fats in the control diet. Did Ancel Keys (co-principal non-author) realise, even as long ago as the mid 1960s, that trans fats were bad? A little stacking of the deck has never been been considered an issue when it might help support the lipid hypothesis.
The experiment, designed to confirm the benefits of PUFA, failed completely. There was zero benefit from cholesterol lowering using dietary linoleic acid. Keys never published the results, hence my use of the term "co-principal non-author" because non published study results cannot have any authors. Happily enough data were excavated by Ramsden et al 40 years later to be published in 2016 as
Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)
There was, overall, no effect on total mortality when comparing the two interventions. To rephrase that: Increasing dietary linoleic acid was no worse than increasing trans fats, overall.
OK. So we could stop there with nothing more insightful than an observation of the moral and scientific bankruptcy of the architects of the lipid hypothesis. Nothing new there.
But what we actually have here is a study comparing two diets, one with a marked increase in the double bond index (DBI) of the lipids vs one with a modest increase in DBI, if we ignore the problems of trans fats.
We have something resembling the CRON mouse study in which lard as the lipid source gave a greater longevity benefit compared to fish oil or soya oil. We can view the present study as an intervention which altered mitochondrial membrane lipid composition in a direction of enhanced ageing based on increased DBI of those membrane lipids. But this time in humans, and with no calorie restriction.
Rather than looking at specific diseases we can ask whether increasing the DBI of your mitochondrial lipids might simply make you biologically older than your chronological age. This should show in the all cause mortality data, irrespective of the cause of death (ignoring "One flew over the cuckoo's nest" scenarios, even though this was a mental hospital study). However this would be hard to isolate in younger people because they are far enough, chronologically, away from death that ageing them by 10 years (a totally fictitious value, merely used for illustrative purposes) wouldn't show up much in all cause mortality. Assuming the risk of death at 40 years of age is similar to that at 50 years of age, nothing will show.
But, if you are 65 years of age and eating 13% of your calories as corn oil derived polyunsaturated fats makes you behave biologically as if you are 75 years of age, this just might show as increased all cause mortality.
Ramsden provides us with these graphs. In people under 65 years of age nothing shows:
but in people over 65 years of age there is visibly increased all cause mortality in the corn oil subjects:
Because the raw data for these graphs could not be recovered it is impossible to perform any sort of statistical analysis but it looks to me like there might be some indication that basing your diet around corn oil PUFA might be worse than eating trans fats, late in life. Given the raw data I suspect it might be possible to calculate how much linoleic acid might shorten your lifespan and by implication I would expect it might also shorten your healthspan, which could actually be worse.
Trans fats come out unexpectedly well. You have to wonder how much more benefit removing linoleic acid might provide, especially if you are an elderly person trying to avoid ARDS in the ITU.