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Prebiotics (FOS and other Oligosaccharides): A reliable method to increase the gut friendly bacteria

James Meschino DC, MS, ROHP
Numerous studies have shown that an imbalance of friendly to unfriendly gut bacteria can cause or aggravate various health conditions. Moreover, supplementation aimed at increasing the number of friendly gut bacteria have been shown to help combat many types of diarrhea, irritable bowel syndrome, eczema, ulcerative colitis, and reduce the incidence of canker sores and vaginal yeast infections, as well as exerting positive effects on the immune system. The friendly gut bacteria consist of lactobacillus acidophilus, L. bulgaricus, L. reuteri, L. plantarum, L. casei, B. bifidus, S. salivarius, S. thermophilus and the yeast Saccharomyces boulardi. Recent studies, however, have shown that taking probiotic supplements (supplements containing friendly bacteria) may not be reliable as random tests performed on probiotic supplements, taken from the shelf of retail outlets, indicate that most products contain no live bacteria by the time they reach the marketplace. These bacteria can only divide and replicate themselves a finite number of times before the final bacteria dies off. As such, it is very difficult for any manufacturer of probiotic supplements to guarantee the number of live bacteria in a supplement at the time of purchase (as opposed to at the time of manufacturing, which is what is usually claimed on the label). In recent years products known as prebiotics have demonstrated an ability to increase the concentrations of friendly gut bacteria, and there is a suggestion that supplementation with prebiotics may be a more reliable method to favorably influence the ratio of friendly to unfriendly gut bacteria. Health practitioners should be aware of the physiology and clinical studies that pertain to the use of prebiotics in clinical practice, as they represent a viable alternative to the use of probiotic supplementation.

General Features of Prebiotics
Prebiotics is a term used to refer to short-chain polysaccharides (carbohydrates) that are not completely digested by the human intestinal tract, but rather serve as a food supply for the friendly bacteria of the large bowel (bifodobacteria and lactobacilli), enhancing their growth and cell division rate.1,2,3

The official definition of Prebiotics is stated as “nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and activity of one species or a limited number of species of bacteria in the colon”.4

Human studies show that supplementation with FOS (fructo-oligosaccharides) increases bifodobacteria and lactobacilli populations in the flora of the large intestine while simultaneously reducing the colonies of detrimental bacteria.  The same has been shown for supplementation with two other Prebiotics; namely inulin and galacto-oligosaccharides (GOS).5-9

Fructo-oligosaccharides (FOS) and inulin consist of short chains of fructose molecules.  Galacto-oligosaccharides consist of short chains of galactose molecules.1,2,3

The estimated average daily intake of FOS from food sources (mostly vegetables) is 800 mg.10  Supplementation studies demonstrate that 2,000-3,000 mg a day of additional FOS can favourably alter the bacteria populations of the large bowel.5-9  Higher doses may help to lower cholesterol, triglycerides and help better regulate blood glucose in type II diabetics.11,12

From a standpoint of general wellness, supplementation with Prebiotics or probiotics have been shown to improve digestion and absorption of some nutrients, enhance detoxification by intestinal mucosal cells, reduce the concentrations of large bowel mutagens and carcinogens, aid elimination processes and favorably affect the immune system of the gut and the systemic immune system.  These effects are related to favorable changes in the concentrations of friendly gut bacteria resulting from pre- and probiotic supplementation.  In regards to immune modulation, these positive effects extend to include reduced hypersensitivity reactions secondary to food sensitivities, improved control of autoimmune conditions and a lessening of skin reactions secondary to food-induced hypersensitivity reactions.4,13,14

An important feature of prebiotic supplementation is its potential impact on reducing risk of colorectal cancer, which is the second leading cause of cancer death in North America (combining statistics for men and women), after lung cancer.  Human studies demonstrate that supplementation with Prebiotics (and probiotics) encourages the growth of lactic acid bacteria (LAB).  Experimental data and some epidemiological evidence indicate that increased LAB protects against colon cancer development.  Experimental data demonstrates that Prebiotics increase the proliferation of LAB which also, through fermentation of Prebiotics and other fiber sources, gives rise to the production of short-chain fatty acids and lowers the pH of the colon; making it a more acidic environment.  Lower pH in the colon is associated with a reduced risk of colon cancer in various studies.  This appears related to an inhibition of certain enzymes that are known to produce bowel carcinogens.  Human studies have shown that prebiotic supplementation reduce concentrations of components that are genotoxic in human colon cells.  Butyrate has been shown to increase the proliferation of normal cells, while inhibiting the proliferation of cancerous cells.  This short-chain fatty acid also induces apoptosis (programmed cell death) of colon cancer cells, under experimental conditions.  It is an important fuel for colon cells and evidence exists to show that colon cells exposed to various carcinogens are less inclined to be transformed into malignant cells in the presence of adequate butyrate supply.  Butyrate has also been shown to increase the concentrations of glutathione transferase enzyme in colon cells.  “Thus, enzyme induction by butyrate, or by the microflora and increased activity by Prebiotics, may be an important mechanism or protection against carcinogen-enhanced colon cancer.”15

Clinical Application and Mechanism of Action

  1. Digestive Disorders, Food Sensitivity and Intolerances, Autoimmune Conditions, Rheumatoid Arthritis, Skin Conditions

Prebiotics may be used to increase friendly gut bacteria (Bifidobacterium, bifidum and longum, and Lacto bacillus acidophilus).  In these conditions a therapeutic dosage of – 2,000-3,000 mg of FOS per day and/or other Prebiotics (inulin, GOS) is commonly utilized.5-9

  1. Lipid Lowering

Prebiotics are metabolized by large bowel bacteria, yielding short chain fatty acids like butyrate.  Butyrate is known to inhibit liver cholesterol synthesis and provide a source of energy for human colon epithelial cells.  Some studies, but not all, demonstrate that supplementing with 8-15 gms of Prebiotics can significantly lower blood cholesterol and triglycerides.  This is not a consistent finding at this time.11,12,16

  1. Type II Diabetes

Some evidence suggests that prebiotic supplementation at 8-15 gm per day can help better regulate blood glucose in type II diabetics. Other studies have not shown this beneficial effect.  Thus, more research is required before any conclusive statements can be made in this regard.12,16

  1. General Wellness

For health promotion purposes (e.g. to reduce concentrations of carcinogens in the large bowel, improve digestion, elimination and immune function) a daily dosage of 500-1,000 mg is often recommended.

Adverse Side Effects and Toxicity
Generally, oligosaccharides are well tolerated.  Some individuals report increased flatulence initially.  At very high levels, (40 gm), FOS and other oligosaccharides may induce diarrhea.1

Drug-Nutrient Interactions
There are no well-known drug interactions with FOS or other Prebiotics.17


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  5. Gibson GR, Beatty EH, Wang X, Cummings JH. Selective stimulation of bifidobacteria in the human colon by oligofructose and mutin.  Gastroenterology 1995;106:975-82.
  6. Bouhnik Y, Fluorié B, Dagay-Abensour L, Pochart P, Gramet G, Durand M, et al. Administration of transgalacto-oligosaccharides increases faecal Bifidobacteria and modifies colonic fermentation metabolism in healthy humans. J Nutr 1997; 127: 444-8.
  7. Bouhmik Y, et al. Short-chain fructo-oligosaccharide administration dose-dependently increases fecal bifodobacteria in healthy humans.  J Nutr 1999;129:113-6.
  8. Roberfroid M. Dietary fibre, inulin and oligosaccharides.  Crit Rev Good Sci Nutr 1993;33:103-48 [review].
  9. Tomomatsu H. Health effects of oligosaccharides.  Food Technology 1994;48(10):61-5.
  10. Gibson GR, Beatty ER, Wang X, Cummings JH. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin.  Gastroenterology 1995;108:975-82.
  11. Jackson KG, Taylor GRJ, Clohessy AM, Wlliams CM. The effect of the daily intake of inulin on fasting lipid, insulin and glucose concentrations in middle-aged men and women. Br J Nutr 1999;82:23-30.
  12. Yamashita, K, Kawai, K, and Itakura, M. Effects of fructo-oligosoccharides on blood glucose and serum lipids in diabetic subjects. Nutr Res 1984;4:961-6.
  13. Roberfroid M. Prebiotics: preferential substrates for specific germs.  Am J Clin Nutr.2001;73(Suppl 2):406S-9S.
  14. Isolauri E, Sutas Y, Kankaanpaa P, Arvilommi H, Salminen S. Probiotics; effects on immunity.  Am J Clin Nutr 2001:73(Suppl 2):444S-50S.
  15. Wollowski I, Rechkemmer G, Pool-Zobel BL. Protective role of probiotics and prebiotics in colon cancer.  Am J Clin Nutr 2001;73(Suppl 2):451S-5S.
  16. Roberfroid M. Dietary fibre, inulin and oligofructose.  A review comparing their physiological effects.  Crit Rev Food Sci Nutr 1993;33:103-48.
  17. Healthnotes online. 2000 Healthnotes, Inc. (
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