Despite what many have erroneously posted, it's not only junk food that can cause heartburn or reflux. I could eat all the junk food in the world and it wouldn't bother me. But the tiniest bit of raw onion or vinegarette dressing puts me in agony for hours.
Junk food = absolutely fine
Raw onion = pure evil
Vinegar = pure evil
Dietary triggers are very individual. Anyone who categorically says "junk food" has no clue what they're talking about.
FWIW, my number one trigger by far is stress. And my gastroenterologist agrees that that is the top trigger for many people.