There are many people foods that cats seem to crave just about as bad as dogs do, but this does not mean the same foods that are good for you are good for your cat.
In very VERY small amounts, it may not seem to make a difference at all. Unfortunately, when you give a kitty any amount of something this automatically seems to translate into, "This is okay for me because mom gave some to me before and I really liked it!" If you leave any out on the counter unattended, your kitty may get to it an eat enough to make herself very sick. Any time there are sudden changes to a cat's diet it may result in an upset stomach, leading to vomiting or diarrhea.
Since pepperoni really isn't all that good for people, I can only be lead to believe that it just can't be very good for your kitten. I happen to have a package of pepperoni I've been snacking on myself, and looking at the ingredients I can already see trouble ahead if my kitties were to get into it.
First off, it's VERY high in sodium, or salt content, as well as saturated fats. Onion or garlic powder are also common ingredients, and onions
are definitely toxic to cats. Sodium Nitrite
is a preservative used in pepperoni that can also be toxic... not just to cats, but to all mammals!
Though I'm certain one little nibble is not enough to cause serious harm to your kitten, it's definitely not a good idea to continue using pepperoni as a treat.