Personally, I won't use metamucil. I did for years and ended up going from IBS A to IBS with severe C. The insolubale fiber in the form of psyllium husk is very harsh for the bowel, IMO. In addition, there are other ingredients in metamucil, and many of the other name brand fibers, that IBS folks do not react well to.
To be honest, I have not yet found a fiber supplement that works for me. I try to get my fiber through food. I find if I incorporate a bit of barley, oats, small amounts of brown rice, yams, butternut squash - those types of foods almost always yield consistent results without all the wierd side effects.
"Dietary fiber is the term for several materials that make up the parts of plants your body can't digest. Fiber is classified as soluble or insoluble.
When eaten regularly as part of a diet low in saturated fat, trans fat and cholesterol, soluble fiber has been associated with increased diet quality and decreased risk of cardiovascular disease. Soluble or viscous fibers modestly reduce LDL cholesterol beyond levels achieved by a diet low in saturated and trans fatty acids and cholesterol alone. Oats have the highest proportion of soluble fiber of any grain. Foods high in soluble fiber include oat bran, oatmeal, beans, peas, rice bran, barley, citrus fruits, strawberries and apple pulp.
Insoluble fiber has been associated with decreased cardiovascular risk and slower progression of cardiovascular disease in high-risk individuals. Dietary fiber may promote satiety by slowing gastric emptying, leading to an overall decrease in calorie intake. Foods high in insoluble fiber include whole-wheat breads, wheat cereals, wheat bran, rye, rice, barley, most other grains, cabbage, beets, carrots, Brussels sprouts, turnips, cauliflower and apple skin.
Many commercial oat bran and wheat bran products (muffins, chips, waffles) contain very little bran. They also may be high in sodium, total fat and saturated fat. Read labels carefully."