Comment by throwaway2037

First, a grain of salt, I'm certainly not an expert, I've just read a bit about the subject.

You know how people like cold pressed extra virgin olive oil? Or avocado oil? Those are "high quality". Industrially refined/deodorized/hexane-extracted soybean, corn, non-high-oleic sunflower/safflower oil, canola tend to be considered to be on the opposite end of the spectrum.

Deodorizing causes the oil to oxidize, as does deep frying, and that makes a variety of nasty byproducts that seem likely to cause systemic inflammation. And from here on HN the other day, "Inflammation now predicts heart disease better than cholesterol" https://www.empirical.health/blog/inflammation-and-heart-hea...

People in this thread are scoffing at RFK saying that beef tallow fries are "healthy", and while I wouldn't go that far, there seems to be good evidence that it's much healthier to deep fry in beef tallow than the soybean oil most switched to in the 90s. Beef tallow is high in saturated fat, which tends to be relatively stable under heat, and very low in polyunsaturated fats, which tend to be the fats that oxidize the worst. Soybean oil, on the other hand, is extremely high in polyunsaturated fat (60% vs 2-4% for beef tallow). And the big problem with commercial deep frying is that the oil is frequently just topped off rather than replaced, so those oxidization byproducts build up over time. More stable fat is really important there.

I also don't know how relevant this is, but soybean frying oil tends to have silicone-based anti-foaming agents mixed in (polydimethylsiloxane is the one I've seen most commonly) - you can find this in the big jugs at Costco if you want to check it out. Silicone generally doesn't seem great to be swallowing - I think it's pretty inert, but it seems likely to me to have mechanical properties that your body's not quite used to dealing with effectively. This is just me being biased about eating something that's pretty obviously not food, though, I haven't seen much on the subject.

Hydrogenated oils are now well known to be bad (trans fats). So Crisco/creamed vegetable shortening, very low quality.

So yeah, there are higher and lower quality oils, especially once they've been degraded via high heat over a long period and oxygen exposure in commercial or industrial frying processes.