Check the label and see if there are any non-core ingredients. There may be hidden sugars. What I do for prepared food is look at the ingredients and see if they are all core. If they are, I use them as core. I find that works for me. For example, Grapenuts. There is no sugar or fat in them and they are made with all core things. Per WW they are not core, but I consider them core and it has not happered my weight loss.
I say, if you find one that is made with core ingredients, try it as core. If you find its affecting your loss, stop using it. Other wise, I say go ahead!
OK, probably will never be allowed to be a ww leader
I've been doing core for a very long time (years). WW seems to not really support it much, at least in my meetings. HTH.