What is the evidence that dietary fiber from whole foods and dietary supplements is beneficial in gastrointestinal health and disease?
Studies of high-fiber diets on the effects of Crohn's disease are few in number, of variable quality and show mixed results.
Foods high in dietary fiber have not been consistently shown to improve the symptoms of irritable bowel syndrome.
A few studies show that dietary fiber increases stool weight and decreases transit time and intraluminal pressure, which are associated with decreased risk of diverticular disease. Long-term prospective studies are needed.
The two studies examining the effect of high-fiber diets on ulcerative colitis showed an increased relative risk of the disease with fiber intakes over 15g per day and a higher relapse rate, compared to drug therapy.
Diets supplemented with fermentable fiber from 20g to 30g of germinated barley foodstuffs (GBF), 60g of oat bran fiber and four grams ispaghula (psyllium) fiber resulted in improvement in ulcerative colitis symptoms in both randomized and non-randomized studies.
Wheat bran and partially hydrolyzed guar gum may produce a placebo effect in improving symptoms of irritable bowel syndrome, but are no more effective than low-fiber treatments. Ispaghula husk produced mixed results in treating the symptoms of IBS.
Supplemental fiber, in doses of 30g per day for soy polysaccharides and 10.5g to 30g per day bran fiber, added to the diet of healthy individuals, does have beneficial effects in terms of increased fecal weight and decreased transit time. Coarse bran may be of benefit in increasing stool weight and decreasing transit time and intraluminal pressure in patients with diverticular disease, but only two studies show this effect and both were negative-quality.
Fiber supplements may also produce a benefit in individuals with stool incontinence, but not in improved intestinal function in individuals with ileal pouch anastomosis. Fiber supplement type also does not appear to affect the rectal cell proliferation in individuals with adenoma.
There is a lack of data examining the impact of fiber from whole foods on outcomes in gastrointestinal diseases. This may be due to the complexity and cost of these studies. However, fiber supplements may produce benefits in the laxation of healthy individuals and fermentable fibers seem to be of benefit to individuals with ulcerative colitis. More research is needed to clarify dose and type of fiber in gastrointestinal health and disease management.
- Grade I means there is Good/Strong evidence supporting the statement;
- Grade II is Fair;
- Grade III is Limited/Weak;
- Grade IV is Expert Opinion Only;
- Grade V is Not Assignable.
- High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
- Moderate (B) means we are moderately confident in the effect estimate;
- Low (C) means our confidence in the effect estimate is limited;
- Very Low (D) means we have very little confidence in the effect estimate.
- Ungraded means a grade is not assignable.
Search Plan and Results: Dietary Fiber vs. Fiber Supplement: GI Disease