If the legend were true, pediatric gastroenterologist David Milov of Nemours Children’s Clinic in Orlando says, “that would mean that every single person who ever swallowed gum within the last seven years would have evidence of the gum in the digestive tract,” but colonoscopies and capsule endoscopy procedures show no such evidence. “On occasion we’ll see a piece of swallowed gum,” he says, “but usually it’s not something that’s any more than a week old.”

Source – https://www.scientificamerican.com/article/fact-or-fiction-chewing-gum-takes-seven-years-to-digest/