[_heimdall]

There's too much there for me to give a great answer here, but I can recommend Dr Michael Eades as a starting point. He wrote a couple books over the years on heart health and has been writing a newsletter for the last few years where he discusses various related topics in detail.

At a super high level, it has to do with how seed oils ("vegetable" oils, etc) are produced and how oxidative they are in the body.