Why Do "Dry" Granola Bars Give Me "the Big D."?

Whenever I have to have a bit of something sweet at work (and the Pure Protein bars just don't do it), I  go to the vending machine in our office building for something to fill the bill.  About the least sugared sweet in the machine are usually these "dry" dense granola bars (the type that are NOT chewy or have a bunch of oats or puffed rice in them or are very sweet, ala Quaker Garnola bars).  These come in a green wrapper, are rather flat, and are made by some healthy-sounding company like "Nature Farms".  They have just a hint of honey flavor to them for sweetening      Seems like though whenever I eat one of the bars within 1-2 hours I get major diarrhea.  I always assumed all the fiber in the bar (which they appear to have a LOT of) would kinda firm things up in the bowel, but they seem to have a laxative effect instead, akin to something with a lot of sugar alchols in it (they don't, according to the nutrition label).   Is this normal for us with high-fiber foods, or is it the result of something else going on with the bars?  

Hmmm, it's Nature Valley you're talking about and they happen to be my favorite vending machine snack  since I've been on a bit of a cinnamon kick lately.  Perhaps it's the fiber in them?  It might just be "one of those things" for you. 

Yep, that's the culprit, Val .. !  

My guess? Wheat flakes ... they're chock full of them ... meaning gluten. Gluten in those, gluten in bread, it all causes the same effects ... gas and diarrhea. I can't eat them either for that reason. I know the kind you're talking about, cuz I used to love them, too. Now I look for and buy the ones with the corn, rice or oats instead, because they don't cause me that problem. 

The thing about fiber... there's different types... and each will do different things. SOLUBLE fiber will (usually) firm you up INSOLUBLE fiber will (usually) make you go, though I don't know if it'll typically cause diarrhea, but insoluble fiber is generally taken for the laxative effect.  I guess if you're overly-sensitive to it, it might cause dhr.

Makes sense, Sean ..    I guess I'll give the Quaker-type ones a try instead, like Amanda suggested ..