Intermittent Fasting

I’m consuming (irony) the Over-eating videos like crazy and loving the information. A quick, two-part question:
When you speak to intermittent fasting, you’ve also mentioned that you have coffee in the morning.

First- if you add stevia or creamer to your coffee, will that affect the fast? and is fattier creamer better than skim milk?

Second- Is caffeine not seen as a way to buffer? I enjoy one coffee in the morning and a decaf in the afternoon. If this is my norm and not a craving that consumes me, is this ok? Or is cutting out all caffeine important?