I think the biggest takeaway from all the research I did is that not all fats are equal. Monounsaturated fats seem to be generally just good. Omega-3, also, seems good, and Omega-6 less so, but part of that could actually be more about the ratios of omega-6 to -3, which can be 15:1 in the Western diet but people have better health outcomes when they bring omega-6 consumption down and increase omega-3 to get the ratio closer to 4:1 to 1:1.
Saturated fats are still debated - some studies did show replacing saturated fats with vegetable fats did reduce cardiovascular disease etc., but then that might be more that there are some protective effects to the vegetable fats and adding them in rather than replacing might have had a similar effect…
Then there are about a million confounding variables. Doing a decent amount of exercise is a big one, because it’s harder to control for than the other common health detriment - smoking, but things like whether your dairy is grass-fed (as it is here in Australia and much of Europe) vs. grain fed apparently makes a big difference (grass fed apparently has a lot more things like CLA, omega-3 fatty acids and Vitamin K2, the benefits of which seem to potentially more than cancel out any problem from the saturated fat).
One other big problem is that a lot of “low fat” products tend to have more sugar added to make up for it.
Too much sugar is bad, yes, and it’s pretty alarming how seemingly little you need to be over that threshold. Literally a single can of coke is almost the entirety of the sugar one should be consuming in a whole day! Fruit juice is also pretty bad unfortunately - basically just as bad as soft drink (I love soft drinks, apple juice, sweet ice tea, it’s been a challenge to cut most of it out!).