Well, I beleive alot of the capsules, if they are packaged that way, are made of cellulose, so plant cell walls, or gelatin. Someone can correct me if im wrong.
Both dont really have calories that you should really be concerened about in the overall picture.
But, why not just take it during your eating window with your meal?
Youre suppose to take vitamins/minerals with food in general, there are some that may absorb better on an empty stomach, like I think calcium was one.