Nutrition

Dietary Fiber

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Dietary Fiber, Fiber, Roughage, Water Soluble Fiber, Insoluble Fiber, Prebiotic

  • See Also
  1. Fiber Supplement
  2. Bulk Laxative
  3. Psyllium
  4. Methylcellulose
  5. Polycarbophil
  • Definitions
  1. Prebiotic
    1. Non-digestible food ingredients mostly of a Carbohydrate base
    2. Improve health by selectively stimulating the growth and activity of existing Bacteria in the colon
    3. Contrast with Probiotics (live Microorganisms as dietary supplements, aiding Digestion and bowel function)
  • Indications
  1. Constipation
  2. Irritable Bowel Syndrome
  3. Diverticulosis
  4. Hemorrhoids
  5. Hypercholesterolemia
  6. Obesity (promotes satiety)
  7. Blood Glucose control (Diabetes Mellitus)
  • Mechanisms
  1. Most high fiber foods contain both water soluble and Insoluble Fiber
    1. Most Fiber Supplements are primarily soluble fiber (dissolves in water)
  2. Water Soluble Fiber (e.g. barley, oats, Psyllium)
    1. Slows Digestion and promotes satiety
    2. Lowers Blood Glucose
    3. Lowers serum LDL Cholesterol
  3. Insoluble Fiber (e.g. wheat bran, rice bran)
    1. Speeds Digestion and transit time
    2. Adds bulk to the stool, making it softer and easier to pass
  4. ` Improves bowel health and decreases Constipation
  • Precautions
  1. Fiber content listed below is approximate
  2. Various texts list different fiber per serving
  • Dosing
  1. U.S. Adult Dietary Guidelines recommend >=25-30 grams of fiber daily
  2. When increasing Dietary Fiber, increase slowly (e.g. 5 gram increase every few days to week)
  3. Fiber intake should be matched by adequate fluid intake (e.g. water)
  • Adverse Effects
  1. Use with 64 oz/day (>1.8 Liters/day) non-caffeinated fluid
  2. Poorly tolerated in atonic colon (e.g. Megacolon)
  3. Gas (bloating, Abdominal Distention, Flatulence)
    1. More common if started too quickly with high dosing
    2. Reduced by gradually increasing fiber intake to 225-30 grams per day
    3. Side effects more likely with dyssynergic Defecation
    4. Side effects are more common with Insoluble Fiber
      1. Insoluble Fiber examples include (Methylcellulose, Citrucel, wheat bran)
      2. In contrast, soluble fiber (psyillium, Metamucil, oat bran) is associated with less gas
  • Drug Interactions
  1. May interfere with absorption of medications
    1. Do not take medications at the same time as Psyllium
    2. Space Psyllium several hours apart from medications
  2. Agents known to be affected
    1. Carbamazepine (Tegretol)
      1. Etman (1995) Drug Dev Ind Pharm 21:1901-6 [PubMed]
    2. Lithium
      1. Perlman (1990) Lancet 335:416 [PubMed]
  • Types
  • Dietary Fiber Sources
  1. Whole grain cereals or breads
    1. All-Bran or 100% Bran Cereal (>8 grams per serving)
    2. Wheaties (2.6 grams per serving)
    3. Shredded Wheat (6 grams per serving)
    4. Grits (5 grams per serving)
    5. Grape-nuts (5 grams per serving)
  2. Fresh fruits
    1. Raspberries (4.5 grams per serving)
    2. Fruits with 1-3 grams fiber per serving
      1. Apple with peal
      2. Orange
      3. Peach
      4. Pear
      5. Strawberries
    3. Fruits with negligible fiber
      1. Grape-fruit has only 0.6 grams fiber per serving
      2. Apple juice has no fiber content
  3. Vegetables (raw better than cooked)
    1. Beans (>8 grams per serving)
      1. Kidney beans
      2. Lima beans
      3. Navy beans
      4. Baked beans
    2. Peas (6 grams per serving)
    3. Corn on the cob (6 grams per serving)
    4. Parsnips (6 grams per serving)
    5. Lentils (4 grams per serving)
    6. Broccoli (3 grams per serving)
    7. Baked Potato with skin (3 grams per serving)
    8. Other vegetables with 1-2 grams fiber per serving
      1. Beets
      2. Cabbage
      3. Carrots
      4. Celery
      5. Corn
      6. Squash
      7. Green beans
      8. Turnips
  4. Other sources
    1. Whole wheat bread (1.3 grams per serving)
  • References
  1. (2026) presc insights 33(9): 8
  2. Brody (1981) Nutrition Book, p. 147
  3. Cheskin in Barker (1995) Ambulatory Medicine, p. 479