What does "fruit in those looms" mean?

Question

It's the 2nd episode of the 5th episode of The Office. Here is the context:

Holly: So, regarding this supplier, approximately how many liaisons have there been?
Meredith: Liaisons, you mean meet-ups? I don’t know, once a month for six years. Something like that.
Michael: Meredith, why don’t you tell Holly… it’s not what she thinks. Nothing unethical happened… and that you just like to sleep around.
Meredith: Am I in trouble here or something?
Michael: No… no, this is just a stupid formality.
Holly: No, it’s not a formality. Now, were these, um, meet-ups just personal? Unrelated to business?
Meredith: Nah, I wouldn’t have done it if it wasn’t for the discount paper. There’s not a lot of fruit in those looms.

Answer 1

It appears that Meredith had affairs with men working for a supplier. She was asked if she did it for personal reasons (that is, she was attracted to them) or for business purposes. She said it was only to get "discount paper" (a type of payment related to stocks and shares). She made a joke which implied that the men did not have very much of interest in their underpants. "Fruit of the Loom" is a well-known brand of men's underwear in the USA.