Some people with IBS may benefit from bulk-forming laxatives. Psyllium seeds (3.25 grams taken three times per day) have helped regulate normal bowel activity in some people with IBS.¹⁰ Psyllium has improved IBS symptoms in double-blind trials.^11,12

The laxatives most frequently used world-wide come from plants. Herbal laxatives are either bulk-forming or stimulating.

Bulk-forming laxatives come from plants with a high fiber and mucilage content that expand when they come in contact with water; examples include psyllium, flaxseed, and fenugreek. As the volume in the bowel increases, a reflex muscular contraction occurs, stimulating a bowel movement. These mild laxatives are best suited for long-term use in people with constipation.

Many doctors recommend taking 7.5 grams of psyllium seeds or 5 grams of psyllium husks, mixed with water or juice, one to two times per day. Some doctors use a combination of senna (18%) and psyllium (82%) for the treatment of chronic constipation. This has been shown to work effectively for people in nursing homes with chronic constipation.¹³

A preliminary trial of the herb psyllium supports the use of this type of fiber in relieving the symptoms associated with diverticular disease and constipation.¹⁴

While fiber from dietary or herbal sources is often useful for constipation, it may also play a role in alleviating diarrhea. For example, 9–30 grams per day of psyllium seed (an excellent source of fiber) makes stool more solid and can help resolve symptoms of non-infectious diarrhea.¹⁵ Alginic acid, one of the major constituents in bladderwrack(Fucus vesiculosus), is a type of dietary fiber and as a result may potentially help relieve diarrhea. However, human studies have not been done on how effective bladderwrack is for this condition.

Psyllium seeds and husks have shown a modest ability to lower blood triglyceride levels in some,^23,24 but not all,²⁵ clinical trials. Further research is needed to assess the effect of psyllium on triglyceride levels more closely, as much of the study so far has focused on lowering cholesterol levels.

Constipation is believed to worsen hemorrhoid symptoms, and thus, bulk-forming fibers are often recommended for those with hemorrhoids. A double-blind trial reported that 7 grams of psyllium, an herb high in fiber, taken three times daily reduced the pain and bleeding associated with hemorrhoids.²⁷ Some healthcare professionals recommend taking two tablespoons of psyllium seeds or 1 teaspoon of psyllium husks two or three times per day mixed with water or juice. It is important to maintain adequate fluid intake while using psyllium.