A good fiber supplement, especially for diarrhea and constipation issues, is pysllium powder, which is found in fiber products such as Metamucil, WebMD notes. A clinical trial of 275 patient showed this supplement to be effective in controlling irritable bowel symptoms.
Metamucil absorbs water and increases the bulk in stool to cause movement in the intestines.
For best results in individuals who don't get sufficient fiber from foods, experts recommend using psyllium three times per day, mixed with plenty of water, according to WebMD. Increase in fiber should be gradual, because ingestion of this drink may cause bloating until the body adjusts to the supplement.