What the manufacturers of your processed food items don’t want you to dwell on, is that your health is not their top priority, profit is. So, as long as they can make something that tastes good and it flies off the shelf, they’re happy. (Of course, it also helps maintain their happiness if no one does a study on any particular food item linking it to health problems.)
Where does this leave us as consumers? Well, first I would say think twice about purchasing processed foods, if it comes wrapped up it’s probably not good for you. But, if that’s not entirely doable, READ THE LABELS! Yes, it is possible to sneak things in that are not specifically accounted for on the label. Usually under the guise of natural and artificial flavors and colors, or something like that, but a little label reading goes a long way. You’ll learn for instance, that even canned vegetables can be suspect. I for one don’t need sugar added to my corn, but most canned corn is sweetened. (I buy frozen)
If you don’t know what the ingredients listed are, don’t buy the product. Ideally there should only be 5 or so ingredients anyway, and they should all sound familiar to you. If all the ingredients could be found in a healthy kitchen you’re doing good. And corn syrup shouldn’t be one of them, even if you do know what it is.
What you’re looking at specifically is the ingredient list, not the percentage of blah blah blah per whatever, if it’s made with junk none of the rest matters.