What Are Prebiotics?


One expert reviews the benefits of prebiotics for better gut health.

Photo © iStockphoto.com/VikaValter

Due at least in part to all of those famous yogurt commercials, consumers are quite familiar with the benefits of probiotics. They are, however, far less aware of the benefits of prebiotics, or prebiotic soluble fiber.

Prebiotic soluble fiber, a concept that gained traction more than two decades ago, is now defined as a selectively fermented substance that results in specific, healthful changes in the composition and/or activity of the gut flora. Research on the effects of prebiotic soluble fiber supplementation indicate beneficial impacts, including:

  • Improved glucose (sugar) and lipid (fat) regulation
  • Reduced appetite and improved weight management in overweight subjects
  • Improved absorption of calcium, magnesium, and other minerals, and increased bone density
  • Increases in the number and metabolic activity of healthful bacteria, primarily Bifidobacteria and Lactobacillus species
  • Better immune function and regulation
  • Improvements in symptoms related to gastrointestinal (GI) disorders and decreased risk of colorectal cancer

This article will focus on the last three of these health benefits: an increase in healthy bacteria, better immune function and regulation, and improvements in symptoms associated with GI disorders.


An Increase in Healthful Bacteria

Supplementation with prebiotic soluble fiber creates what is known as “the prebiotic effect”-changes in the makeup and/or activity of certain health-promoting bacteria. These beneficial effects are related to prebiotic soluble fiber’s metabolism and ability to produce vitamins, antioxidants, and bacteriocins. (Bacteriocins are narrow-spectrum natural antibiotics that help keep their bacterial competition at bay while, at the same time, inhibiting some “bad” bacteria that cause colonic disease.)

Prebiotic soluble fibers have several common features:

  • Selective stimulation of the growth and/or activity of one or a limited number of intestinal bacteria associated with health and well-being
  • Resistance to gastric acidity and digestive enzymes, which enables prebiotic soluble fiber to survive until it gets to the large intestine
  • Fermentation (digestion) by intestinal bacteria

A sizeable body of research, both on humans and animals, demonstrates that supplementing with a variety of dietary soluble fibers types results in increases in Bifidobacteria, Lactobacillus, or both. These and other healthful bacteria improve health in a variety of ways. By feeding on prebiotic soluble fiber, their primary food source, they increase in number and metabolic activity, which as a result produces short-chain fatty acids, vitamins, antioxidants, and bacteriocins.

Short-chain fatty acids do a number of significant things. One type of short-chain fatty acid feeds the cells that make up the gut lining, helping to keep the cells healthy and thus supporting their barrier function. This type of short-chain fatty acid also regulates these cells’ growth and differentiation-factors that may contribute to the fatty acid’s role in helping to reduce the risk of colon cancer. Other short-chain fatty acids are absorbed and transported to the liver, where they favorably affect glucose metabolism and also appear to inhibit cholesterol synthesis and regulate the deposit of fat.


Improved Immunity

There are many different kinds of immune-system cells. These cells perform a variety of functions and create a variety of molecules that affect how the immune system functions. Although no single immune marker accurately reflects overall immune function, examining many markers in different situations can paint a picture of immune function and modulation in both hyper-immune conditions (such as autoimmune disorders) and hypo-immune ones (such as infection).

Adding prebiotic soluble fiber to the diet benefits the immune system in many ways. For instance, in infants who were not breastfed, prebiotic supplementation has been shown to create a significantly higher concentration of immune antibodies.[1][2] In elderly adults, supplementation helped to increase natural killer cell activity, increase production of an anti-inflammatory substance, and decrease production of two pro-inflammatory substances. In infants with a high risk of allergies, prebiotic supplementation reduced blood levels of antibodies that cause allergic reaction and reduced the incidence of atopic dermatitis.[3] Experimental data from animal studies of prebiotic supplementation showed similar benefits.

According to the author of one review article on prebiotic soluble fiber, many animal and human studies suggest that some aspects of innate and adaptive immunity of the gut and the entire immune system are positively affected by prebiotic supplementation.[4] Additionally, a number of studies have shown that prebiotics play a role in helping to overcome infections. This body of work, along with other studies, strongly suggest that prebiotic supplementation improves the body’s response to certain infections and improves inflammatory conditions.


Help for Serious Bowel Conditions

Research demonstrates that prebiotic soluble fiber may help to improve the symptoms of gastrointestinal disorders[5] and may help decrease the risk of colorectal cancer[6]. People with irritable bowel syndrome (IBS) experience chronic recurring abdominal pain or discomfort coinciding with diarrhea, constipation, or both. In these cases, prebiotic supplementation has been shown to significantly reduce the incidence and severity of symptoms while increasing quality of life.[7]

An imbalance of pro-inflammatory and immune-regulating substances in the gut’s mucous membranes causes inflammatory bowel disease (IBD), a chronic disorder characterized by intestinal inflammation, ulceration, and narrowing of the intestines. Symptoms include diarrhea, urgency and incontinence, and severe abdominal pain and rectal bleeding, and can have a profound negative impact on the ability to absorb nutrients as well as on the patient’s quality of life. Studies on patients with ulcerative colitis, a type of IBD, have shown significant reductions in inflammation following prebiotic supplementation, with increased mucosal Bifidobacteria and decreased pro-inflammatory substances.[8] Similar changes have been seen in patients with Crohn’s disease, another type of IBD, with patients seeing a significant reduction in disease activity and with 40% of the treated patients entering disease remission.[9]

Evidence from a number of studies suggests that changes to the colon’s bacteria may be a factor that leads to cancer. It follows, then, that improving the numbers and activity of healthful gut bacteria may interfere with the process of carcinogenesis.[10],[11] Animal studies have shown evidence of decreased pre-cancerous lesions and decreased tumor incidence following prebiotic supplementation.[12],[13],[14],[15],[16],[17],[18],[19] Human studies examine changes in biomarkers of colon cancer, such as DNA damage and cell proliferation in the colon’s mucous membranes.[20] A randomized, double-blind trial of prebiotic supplementation in patients with resected polyps or colon cancer showed favorable changes in multiple colon cancer biomarkers. [19]



A vast body of research tips the scale in favor of the benefits of prebiotic supplementation. Prebiotic supplementation can offer significant help to people who face serious gastrointestinal conditions and may help to improve symptoms implicated in multiple bowel issues such as IBS, IBD, and colorectal cancer. In addition, prebiotic soluble fibers improve inflammatory conditions and the body’s response to certain infections. These “prebiotic effects” make this natural, non-invasive supplementation a smart choice.


Peter Swann, MD, FAAFP, FACOEM, Chief Medical Officer of ISOThrive LLC, is a subject matter expert in the fields of prebiotics, probiotics, and the microbiome. He is a board-certified family physician with a focus on patient health, wellness, and prevention. A graduate of Dartmouth College and Tufts University School of Medicine, Dr. Swann is also a Fellow of the American Academy of Family Physicians and the American College of Occupational and Environmental Medicine.



[1] Scholtens P et al., “Fecal secretory immunoglobulin A is increased in healthy infants who receive a formula with short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides,” Journal of Nutrition, vol. 138, no. 6 (June 1, 2008): 1141–1147

[2] Bakker-Zierikzee AM et al., “Faecal SIgA secretion in infants fed on pre- or probiotic infant formula,” Pediatric Allergy and Immunology, vol. 17, no. 2 (March 2006): 134–140

[3] Moro G et al., “A mixture of prebiotic oligosaccharides reduces the incidence of atopic dermatitis during the first six months of age,” Archives of Disease in Childhood, vol. 91, no. 10 (October 2006): 814–819

[4] Lomax AR et al., “Prebiotics, immune function, infection and inflammation: a review of the evidence,” The British Journal of Nutrition, vol. 101, no. 5 (March 2009): 633–658

[5] Paineau D et al., “The effects of regular consumption of short-chain fructo-oligosaccharides on digestive comfort of subjects with minor functional bowel disorders,” The British Journal of Nutrition, vol. 99, no. 2 (February 2008): 311–318

[6] Buddington KK et al., “Dietary oligofructose and inulin protect mice from enteric and systemic pathogens and tumor inducers,” The Journal of Nutrition, vol. 132, no. 3 (March 2002): 472–477

[7] Silk D et al., “Clinical trial: the effects of a trans-galactooligosaccharide prebiotic on faecal microbiota and symptoms in irritable bowel syndrome,” Alimentary Pharmacology & Therapeutics, vol. 29, no. 5 (March 1, 2009): 508–518

[8] Furrie E et al., “Synbiotic therapy (Bifidobacterium longum/Synergy 1) initiates resolution of inflammation in patients with active ulcerative colitis: a randomised controlled pilot trial,” Gut, vol. 54, no. 2 (February 2005): 242–249

[9]Lindsay JO et al., “Clinical, microbiological, and immunological effects of fructo-oligosaccharide in patients with Crohn’s disease.,” Gut, vol. 55, no. 3 (March 2006): 348–55

[10] Rowland I, “The role of the gastrointestinal microbiota in colorectal cancer,” Current Pharmaceutical Design, vol. 15, no. 13 (2009): 1524–1527

[11] Cipe G et al., “Relationship between intestinal microbiota and colorectal cancer,” World Journal of Gastrointestinal Oncology, vol. 7, no. 10 (October 15, 2015): 233–240

[12] Verghese M et al., “Dietary inulin suppresses azoxymethane-induced preneoplastic aberrant crypt foci in mature fisher 344 rats,” The Journal of Nutrition, vol. 132, no. 9 (September 2002): 2804–2808

[13] Poulsen M et al., “Different effects of short- and long-chained fructans on large intestinal physiology and carcinogen-induced aberrant crypt foci in rats,” Nutrition and Cancer, vol. 42, no. 2 (2002): 194–205

[14] Reddy BS et al., “Effect of dietary oligofructose and inulin on colonic preneoplastic aberrant crypt foci inhibition,” Carcinogenesis, vol. 18, no. 7 (July 1997): 1371–1374

[15] Buddington et al., “Dietary oligofructose and inulin protect mice from enteric and systemic pathogens and tumor inducers”

[16] Jacobsen H et al., “Carbohydrate digestibility predicts colon carcinogenesis in azoxymethane-treated rats,” Nutrition and Cancer, vol. 55, no. 2 (July 2006): 163–170

[17] Caderni G et al., “Identification of mucin-depleted foci in the unsectioned colon of azoxymethane-treated rats: correlation with carcinogenesis,” Cancer Research, vol. 63, no. 10 (May 15, 2003): 2388–2392

[18] Pierre F et al., “Short-chain fructo-oligosaccharides reduce the occurrence of colon tumors and develop gut-associated lymphoid tissue in min mice,” Cancer Research, vol. 57, no. 2 (January 15, 1997): 225–228

[19] Femia AP et al., “Antitumorigenic activity of the prebiotic inulin enriched with oligofructose in combination with the probiotics Lactobacillus rhamnosus and Bifidobacterium lactis on azoxymethane-induced colon carcinogenesis in rats,” Carcinogenesis, vol. 23, no. 11 (November 2002): 1953–1960

[20] Roberfroid et al., “Prebiotic Effects: Metabolic and Health Benefits.”



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