English Translation
Eating too much junk food will make you fat.
If we omitted the “zu” before “essen”, would it still be correct?
It would be clear what you meant, but it is technically wrong. In English you could say “To eat too much junk food is bad” or “It’s bad to eat too much junk food”, but it sounds wrong to say “Eat too much junk food is bad” or “It’s bad eat too much junk food”.
That being said, we can reword the sentence in German to avoid “zu” in front of the verb:
Wenn man zu viel Junkfood isst, wird man dick.
Wenn man nicht dick werden will, muss man kein Junkfood essen.