"A lot" is a stretch. There is some evidence in mice and a few hypothesis but I certaintly wouldn't say "a lot." The exception to this I would say is soybean oil. There is a decent amount of research pointing in direction that soybean oil isn't great.
Added oil should be kept at minimum. It doesn't matter the source. But of course this is not the main reason for the obesity epidemic; people just like to find easy culprits instead of looking at the culture around food in the US.
