Fiber is WAY important - Michael Fumento devotes an entire CHAPTER on "The Fiber Factor" in his book
Fat of the Land. When I did Optifast back in 1990, a fiber supplement was required. However, I cannot STAND that icky gritty Metamucil feeling in my mouth so I used those FiberCon tablets.
These days, I prefer to get my fiber the natural way - from foods. Cereals like Fiber One and All-Bran have a TON of fiber in them (so introduce them gradually!). And of course there's all those lovely fiberous vegetables that we all know are SO good for us.
And if you have, um, 'reactions'...there's always Beano.