PUFAs = Poly Unsaturated Fatty Acids eg "vegetable" oils meaning seed oils: corn oil, soybean oil, cottonseed oil, rapeseed (canola) oil, etc. Unstable and prone to oxidation into toxic substances, especially when heated. Most of PUFAs are linoleic acid.
Trans fat = PUFAs with hydrogen chemically added to make them more saturated. Frankenfats that do not generally exist otherwise.
Mono unsaturated fat = fat with one double hydrogen bond but one unsaturated bond eg olive oil. More stable than PUFAs by being less prone to oxidation.
Saturated fat = fats with double hydrogen bonds. Highly stable, highly resistant to oxidation.
The “science” wrapped around public policies on fats and heart health is a pile of manure.
Heart disease remains the #1 killer, a huge boon to an industry for keeping people employed in farming and industry and hospitals. Need more be said than that? Progress is measured by any sane person by seeing improving metrics. This the medical profession has utterly failed to do. But it has succeeded in medicalizing generations of people damaged by their bad eating advice, via nasty chemicals ("medicine") to address proxies for disease for which there is no good science, e.g., statins for cholesterol with a clown show of continuously changing hypotheses, needed because the prior ones kept not cooperating. And you have a ringside seat at this circus.
Mass experimentation that failed
The history of this debacle is fascinating; see The Big Fat Surprise: Why Butter, Meat, and Cheese Belong in a Healthy Diet @AMAZON.
About 70 years ago, we were told that saturated fats are bad for you. That scientific garbage is only now slowly starting to decompose, but intellectual dishonesty and dogma die a slow death. It will take decades more. Just ask your doctor and you can be assured of boilerplate advice.
When an entire profession claims X is bad, thus Y is better, you had better show that Y is better. This the medical profession has never done for fats. It’s all clown-shown “science” using all the intellectually dishonest tricks ever invented. And it’s now a very big business.
Early in the 1900's, seed oils were found to be far more useful when hydrogenated. So the public was then told to eat trans-fats to replace those 'evil' saturated fats. Which many did, as they are much cheaper than butter or lard or tallow. And remember the eggs and cholesterol thing, now understood as debunked?
Decades passed and lo! Trans fats are still allowed but thought to be the worst of all. But maybe they aren’t?
Now, we are told to eat PUFAs for heart health. So restaurants went from beef tallow or lard to trans fats to PUFAs.
There is a “small” problem there; PUFAs are highly prone to oxidation, lacking the double hydrogen bonds of saturated fats. Oxidation forms 100+ Frankenfats, some of which are highly toxic. Especially so when heated: they are the worst possible fats for for cooking, oxidizing into well over 100 frankenfat molecules form. The vapors are so nasty, coating things with sludge and varnish, that harsh chemical solvents and special ventilation systems are needed to deal with the problem. This was never a problem with beef tallow, or eeven trans fats.
When a substance is chemically unstable and can degrade into oxides and peroxides, is it even credible that you would want to eat that shit? Especially foods already high in inflammatory Omega 6 fatty acids?
The human body only needs 1% to 2% of its fats from PUFAs. What happens when you incorporate 10%, 30%, 50% fat in the form of PUFAs into your body? You get cells and fat that are prone to damage.
Consumers chow-down french fries and fried foods, ingesting highly-damaged PUFAs with over 100+ frankenfats for which no one knows the deleterious issues. And maybe that is the REAL reason for escalating heart disease.
Some needed, but not much
Check on your own fat types incorporated into body tissue with OmegaQuant Omega-3 Index Complete Fatty Acid Profile Blood Test Kit @AMAZON.
When you kill and eat a grass-fed cow or free-ranging chicken, you get a mix of what natured intended. Not so with corn or soy-fed animals, which have a radically different fatty acid profile. But even that is relatively natural.
But when you eat seed oils, there is absolutely nothing natural going on. You get a massive dose of fats that you could never have eaten otherwise. And these fats are likely highly damaged/oxidized from heating. Good luck with that.
There are now is at least one startup claiming to produce superior oils, via fermentation.