Some vegetable fibers, such as guar and pectin, are soluble in water. Another type of fiber, which some of us call roughage, is not water-soluble. Certain insoluble fiber products, such as psyllium, have long been used as laxatives. Consumption of large amounts of dietary fiber is usually unpleasant, because both types can cause abdominal discomfort, diarrhea, and flatulence. Sources of insoluble fiber include most salad vegetables.
Soluble fiber is found in many beans, such as garbanzos, and in certain fruits, such as apples.
I first learned of attempts at using fiber as an adjunct to the treatment of diabetes about twenty years ago. At that time, Dr. David Jenkins, in England, reported that guar gum, when added to bread, could reduce the maximum postprandial blood sugar rise from an entire meal by 36 percent in diabetic subjects. This was interesting for several reasons. First of all, the discovery occurred at a time when few new approaches to controlling blood sugar had appeared in the medical literature. Second, I missed the high-carbohydrate foods I had given up, and hoped I might possibly reinstate some.