Sunsweet Prune Juice “Fit on the Inside” Ad

I just saw an ad where the question is posited: “Why do people count on Sunsweet Prune Juice to stay fit on the inside?”

Um, “fit on the inside”? Yes, why do people count on Sunsweet Prune Juice to stay fit on the inside? Is it to prepare for the Colon Olympics?

Here’s the spot that’s fit on the inside:

http://www.ispot.tv/ad/7wCY/sunsweet-prune-juice-fit-on-the-inside