II. Definitions
- Prebiotic
- Non-digestible food ingredients mostly of a Carbohydrate base
- Improve health by selectively stimulating the growth and activity of existing Bacteria in the colon
- Contrast with Probiotics (live Microorganisms as dietary supplements, aiding Digestion and bowel function)
III. Indications
- Constipation
- Irritable Bowel Syndrome
- Diverticulosis
- Hemorrhoids
- Hypercholesterolemia
- Obesity (promotes satiety)
- Blood Glucose control (Diabetes Mellitus)
IV. Mechanisms
- Most high fiber foods contain both water soluble and Insoluble Fiber
- Most Fiber Supplements are primarily soluble fiber (dissolves in water)
- Water Soluble Fiber (e.g. barley, oats, Psyllium)
- Slows Digestion and promotes satiety
- Lowers Blood Glucose
- Lowers serum LDL Cholesterol
- Insoluble Fiber (e.g. wheat bran, rice bran)
- Speeds Digestion and transit time
- Adds bulk to the stool, making it softer and easier to pass
- ` Improves bowel health and decreases Constipation
V. Precautions
- Fiber content listed below is approximate
- Various texts list different fiber per serving
VI. Dosing
- U.S. Adult Dietary Guidelines recommend >=25-30 grams of fiber daily
- When increasing Dietary Fiber, increase slowly (e.g. 5 gram increase every few days to week)
- Fiber intake should be matched by adequate fluid intake (e.g. water)
VII. Adverse Effects
- Use with 64 oz/day (>1.8 Liters/day) non-caffeinated fluid
- Poorly tolerated in atonic colon (e.g. Megacolon)
- Gas (bloating, Abdominal Distention, Flatulence)
- More common if started too quickly with high dosing
- Reduced by gradually increasing fiber intake to 225-30 grams per day
- Side effects more likely with dyssynergic Defecation
- Side effects are more common with Insoluble Fiber
- Insoluble Fiber examples include (Methylcellulose, Citrucel, wheat bran)
- In contrast, soluble fiber (psyillium, Metamucil, oat bran) is associated with less gas
VIII. Drug Interactions
- May interfere with absorption of medications
- Agents known to be affected
IX. Types: Dietary Fiber Sources
- Whole grain cereals or breads
- All-Bran or 100% Bran Cereal (>8 grams per serving)
- Wheaties (2.6 grams per serving)
- Shredded Wheat (6 grams per serving)
- Grits (5 grams per serving)
- Grape-nuts (5 grams per serving)
- Fresh fruits
- Raspberries (4.5 grams per serving)
- Fruits with 1-3 grams fiber per serving
- Apple with peal
- Orange
- Peach
- Pear
- Strawberries
- Fruits with negligible fiber
- Grape-fruit has only 0.6 grams fiber per serving
- Apple juice has no fiber content
- Vegetables (raw better than cooked)
- Beans (>8 grams per serving)
- Kidney beans
- Lima beans
- Navy beans
- Baked beans
- Peas (6 grams per serving)
- Corn on the cob (6 grams per serving)
- Parsnips (6 grams per serving)
- Lentils (4 grams per serving)
- Broccoli (3 grams per serving)
- Baked Potato with skin (3 grams per serving)
- Other vegetables with 1-2 grams fiber per serving
- Beets
- Cabbage
- Carrots
- Celery
- Corn
- Squash
- Green beans
- Turnips
- Beans (>8 grams per serving)
- Other sources
- Whole wheat bread (1.3 grams per serving)
X. References
- (2026) presc insights 33(9): 8
- Brody (1981) Nutrition Book, p. 147
- Cheskin in Barker (1995) Ambulatory Medicine, p. 479