Processed carbohydrates will by definition hit you hard. Added oil is also hard. Try intact grains, e.g. rice, quinoa, millet, barley, etc. Even whole wheat bread or pasta will hit harder than boiled wheat grains.
Added oil is just fat, not bad for you. Specifically since op mentioned keto.
But they're not talking about keto if they're eating fries etc. Added oil is not good - in excess fat builds up in the cells and is responsible for insulin resistance. With ketosis this is temporarily staved off, but you will still likely have insulin problems when you go off keto, it doesn't actually fix anything, just offer temporary relief.