I used to love grapes. But eating them now... I might as well just throw a bunch of sugar in my mouth and chug it down. I'd guess they have a certain amount of wellness in wine as reservatol, but jeez, you can barely find grapes that aren't super-sugared out anymore (like corn!). That said, there's got to be some heirloom or old varieties left that aren't super-fructose bombs. Off to look that up.
Most grapes you're going to find at the store are little sugar bombs.
That said, if you aren't low carbing, there's a lot of value in enjoying your favorite (whole) foods once in a while. Some sweet fruit can be a nice treat.
I wonder if the different types of grapes do actually contain more/less sugar. I assume red have more than green, and probably the purple ones (that are huge) have the least. I couldn't find any research on this online, though I am sure one exists. Maybe plug different kinds into fit day and see? Also-did you know the sugar in grapes is turned into alcohol using yeast? Good to know for those who are sensitive. Learn something new every day!
I'm investigating the whole FODMAPS thing, and according to one of the primary sources I'm using (http://www.ibsfree.net/ibsfree_at_last/), grapes are high in both fructose and fructans. As I'm trying to mitigate some gastrointestinal dysfunction, I'll be cutting out grapes - sadly.
Like everyone else said, watch out for the sugar. Otherwise, I enjoy them in moderation, really just like any other fruit. I know some fruits have more sugar than others and all the rest, but considering that I stay away from all of the refined sugars and treats I used to eat constantly without even thinking, I figure I can get away with the occasional fruit, no matter what it is.