Originally Posted by onesnowyowl

One thing I would definitely do is look at the balance of fiber in your diet--Fiber One is fine and dandy, but it mainly consists of insoluble fiber. You might want to think about increasing your soluble fiber intake; many of the health benefits associated with fiber are attributed to soluble fiber.

I think you do have a sensitivity somewhere, and I'm not sure it's the fiber that's the cause; I eat upwards of 30g of fiber a day without issue. Admittedly, I am not getting my fiber from a single source. Instead, I eat whole-grain breads, lots of legumes, lots of fruits and vegetables, and various kinds of cereals (oatmeal with flax seed is a favorite). Fruits, veggies, and legumes are all good sources of soluble fiber. Yum.

Try keeping a food diary for a couple of weeks. Every time you have an issue, make note of it. You may notice a pattern before too long.