it's the oils. Processed oils aren't great for us at all & the processes necessary to make them 'stable' enough to be used in mass produced foods are even worse.
Heating certain oils also can create a very toxic product.
We are starting to hear (at least in mainstream media now - it has been widely known for years though) how the increase in heart disease isn't actually linked to saturated fats as we have been told by govt's and doctors and media for years now, but to increase in consumption in toxic fats such as processed heat treated vege oils, margarine etc.
How ironic that the fat sold to us as a 'healthy' alternative is actually the cause of the huge spike in heart disease. Is is because of the processes applied to the 'healthy oils' - like heating them to high temps and hydrogenating them, to make a liquid solid - it completely changes the oils chemically.
To a lessor degree the same processes will have been done to the oil on oven chips. And chip shop chips are cooked in vegetable oils that have been heated to high temperatures over and over and over.
I CBA to provide links - but a quick google will reveal all you need to know.
The mainstream media will be increasingly reporting "step away from the margarine" now. Back to butter!