Garlic, one of my favorite prebiotics


What Are Prebiotics?

Most people know what a probiotic is but what, exactly, is a prebiotic? Prebiotics are non-digestable but fermentable soluble fibers that stimulate the growth of beneficial gut flora in the colon. I like to think of prebiotics as fertilizer for your friendly colonic bacteria.

There are two types of prebiotics. Shorter-chain prebiotics like oligofructose that contain 2-8 links of saccharide per molecule. These are more apt to be fermented by colonic bacteria in the right side of the colon. Longer-chain molecules like inulin feed beneficial gut bacteria on the left side of the colon. A full-spectrum prebiotic like inulinFOS feeds both.

A number of foods contain prebiotic-soluble fibers. Good sources include raw chicory root, raw Jerusalem artichoke, dandelion greens, raw garlic, raw leek and raw onion. While cooking will reduce the availability of these fibers for fermentation, I nevertheless highly recommend you include these foods in your diet. Just be aware that if gas or bloating is an issue for you, the fermentation of these foods by your colonic bacteria can cause a lot of discomfort and potential embarrassment if you know what I mean. And if you suffer from small-intestinal dysbiosis or fructose malabsorption, these foods can add to your discomfort so be careful. If this is a problem for you, cut back on the amount you eat or consider supplementing instead with a prebiotic powder. This allows you more control over the amount you ingest.

The following are benefits derived from ingesting prebiotics:

Prebiotics and Intestinal Function

Many of us at one time or another have struggled with constipation. For those with IBS or other gut disorders, it can be a constant companion. Inulin-type fructans have been demonstrated to offer relief from this problem.

In one study done in Germany, 35 elderly and hospitalized female patients suffering from constipation had their hospital food supplemented for 19 days either with the milk sugar lactose or the prebiotic inulin to see if there would be any change in bowel movement frequency. Before the study began all patients had only one or two bowel movements per week so we’re talking serious constipation here.

Those treated with lactose had results that varied widely. Some reported more frequent bowel movements while others experienced even worse constipation along with increased gas. In the inulin group, however, 7 out of 10 experienced improvements between weeks eight and nine. Stools were softer and easier to pass. Not only was stool frequency improved, but an increase in friendly Bifidobacterium was noted from collected stool samples as well as decreases in potentially pathogenic Enterococci bacteria. (1)

In a randomized, placebo-controlled study conducted in France on elderly volunteers, supplementing with 15 grams of inulin daily for 28 days led to a significant increase in friendly bifidobacteria as well as increased frequency in bowel movements. (2)

In yet another study conducted in an elderly population suffering from constipation, supplementing with both a probiotic and prebiotic resulted in an increase in stool frequency and increased measures of well-being and quality of life. (3)

Another randomized, placebo-controlled study was performed in five French hospitals to study the effects of prebiotics on patients reporting minor bowel disorders. 105 patients were randomized into two groups. One group received 5 grams of prebiotic daily while the other group was given a placebo. The study lasted six weeks. On day 43 of the trial, those receiving prebiotics experienced a 43.6% reduction in their symptoms as opposed to an increase of 13.8% in reported symptoms in the placebo group. 75% of the subjects in the treatment group reported improvements in their symptoms as opposed to 53.8% of the placebo group that saw no change. A quality of life questionnaire showed an increase in satisfaction in the prebiotic group and either no change or worsening quality of life scores in the placebo group. (4)

Increases in Bifidobacterium have been seen in infants after supplementing with prebiotics as well as in children, adults and the elderly with or without supplementation with a probiotic. (1 – 9)

Prebiotics and Short-Chain Fatty Acids

Apart from encouraging the growth of friendly colonic gut flora, there are a number of short-chain fatty-acid metabolites produced during their fermentation. Short-chain fatty acids (SCFA) are organic fatty acids of one to six carbon atoms in length. They are water-soluble and easily absorbed by the body. SCFAs are also found naturally in fruits, vegetables and milk fat.

The three main SCFAs produced are acetate, propionate and butyrate.

Acetate is produced in the colon by bacterial fermentation, but quickly departs the colon to be used by the liver, muscles and other tissues throughout the body. In pigs, acetate has been found to stimulate sodium uptake. If this is true for humans, its presence may help to curb recurrent diarrhea. (10)

Propionate is largely used to fuel liver function. Propionate may also reduce hunger in humans by increasing satiety signals. (11)

Butyrate is a major source of energy for the cells lining the colon providing up to 60-70% of the energy requirements for these cells. Simultaneously, it can provide the body with between 7-10% of its energy needs. (12) Butyrate has been shown to prevent carcinogenic activity in rats by inhibiting mammary tumor progression. (13) Finally, it has been proposed that the inability to utilize butyrate properly could be a predisposing factor in the development of ulcerative colitis. (14)

Prebiotics and Conjugated Linoleic Acid

Bifidobacterium is also responsible for producing conjugated linoleic acid (CLA). (15) B. breve was the particular strain most likely to produce this important substance.

CLA is found naturally in the milk and tissue fat of ruminant animals and in the highest concentrations in grass-fed cows. CLA has been shown to have a number of positive physiological activities such as inhibiting weight gain, and having anti-diabetic, anti-carcinogenic and anti-atherosclerotic properties. (16)

In pre-diabetic Zucker fatty rats, CLA was shown to normalize glucose levels. (17) CLA has also been shown to regulate the leptin hormone in both rats and mice. (18) Leptin is a hormone produced in fat tissue that regulates long-term weight homeostasis.

Finally, CLA has been positively shown to influence calcium and bone metabolism. (19 – 21) Could gut dysbiosis be part of the reason so many suffer from osteopenia and osteoporosis?

Prebiotics and Health

First, I want to cover some animal studies before I discuss studies in humans. As always, keep in mind that these studies may or may not be relevant to us, but their results are intriguing nonetheless.

In quails that were purposely infected with various species of Clostridium and E. coli pathogens in order to study the progression of necrotizing enterocolitis, encouraging the growth of bifidobacteria by including prebiotics in their feed prevented the overgrowth of these harmful organisms. (22) (23) Necrotizing enterocolitis is death of intestinal tissue often seen in very sick or premature infants, although it may also afflict the elderly.

In two pig studies, supplementing with prebiotics protected the pigs from colonization with pathogenic bacteria including the cholera toxin. (24) (25)

In mice, supplementing with prebiotics reduced Candida albicans populations and increased survival rates. Moreover, supplementing with a probiotic and prebiotic showed improved intestinal motility, increased intestinal barrier function and decreased pathogenic translocation.  In mice infected with Salmonella and Listeria, supplementation with prebiotics significantly reduced mortality from these infections. (26) (27) Finally, supplementing with inulin either alone or with probiotics has demonstrated an anti-colon cancer effect in mice. Both pre-cancerous lesions and tumors were reduced after supplementing with prebiotics. (28) (29)

Human clinical trials have shown that supplementing with prebiotics can protect against colonization by harmful bacteria. In a study of critically ill patients at risk of sepsis in an intensive care unit, supplementing with oligofructose reduced the number of pathogens sampled from their nasogastric fluid. (30)

In patients suffering from Clostridium difficile diarrhea, prebiotics suppressed further C. difficile colonization and increased Bifidobacterium resulting in less diarrhea and a shorter hospital stay. (31)

In those suffering from ulcerative colitis, bifidobacteria populations are 30-times lower than in healthy controls. In one study, supplementing with both a probiotic and prebiotic for one month resulted in 42-fold increase in bifidobacteria. Decreases in chronic inflammation and regeneration of colonic tissue was also seen. (32) (33) In Crohn’s disease, supplementing with prebiotics also increased bifidobacteria and reduced levels of inflammation. (34)

 Other Health Benefits

Either supplementing with bifidobacteria or encouraging its growth has been shown to increase HDL levels in a small group of women, reduce lactose intolerance, have a modest effect in preventing infectious diarrhea, reduce triglycerides levels, improve glucose control and reduce inflammation and intestinal permeability. (35 -42)


The take home message from all these studies is that fermentable-soluble fibers should be part of a healthy diet. Feed your friendly gut flora so that they in turn can protect and nourish you.


  1. Kleessen B., Sykura B., Zunft H-J., Blaut M., 1997.  Effects of inulin and lactose on fecal microbiota, microbial activity, and bowel habit in elderly constipated persons. American Journal of Clinical Nutrition 65: 1397-1402.
  2. Marteau P., Jacobs H., Cazaubiel M., Signoret C., Prevel J.M., Housez B., 2011. Effects of chicory inulin in constipated elderly people: a double-blind
  3. controlled trial. International Journal of Food Sciences and Nutrition 62(2): 167-70.
  4. Zunft H-J., Hanisch C., Mueller S., Koebnick C., Blaut M., Dore J., 2004. Synbiotic containing Bifidobacterium animalis and inulin increases stool frequency in elderly healthy people. Asia Pacific Journal of Clinical Nutrition 13: S112.
  5. Paineau D, Payen F, Panserieu S, et al., 2008. The effects of regular consumption of short-chain fructo-oligosaccharides on digestive comport of subjects with minor functional bowel disorders. British Journal of Nutrition 13: 311-318.
  6. Gibson G.R., Beatty E.R., Cummings J., 1195. Selective fermentation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 108: 975-982.
  7. Rao A., 2001. The prebiotic properties of oligofructose at low intake levels. Nutritional Research  21: 843-848.
  8. Langlands S.J., Hopkins M.J., Coleman N., Cummings J.H., 2004. Prebiotic carbohydrates modify the mucosa associated microflora of the human large bowel. Gut 53: 1610- 1616.
  9. Bartosch S., Woodmansey E.J., Paterson J.C.M., McMurdo E.T., Macfarlane G.T., 2005. Microbiological effects of consuming a synbiotic containing Bifidobacterium bifidum, Bifidobacterium lactis, and oligofructose in elderly persons, determined by real-time polymerase chain reaction and counting of viable bacteria. Clinical Infectious Diseases 40: 28-37.
  10. Argenzio, R.A., Whipp, S.C., 1979. Inter-relationship of sodium, chloride, bicarbonate and acetate transport by the colon of the pig. The Journal of Physiology 295, 365–381.
  11. Arora, T., Sharma, R, Frost, G., 2011. Propionate. Anti-obesity and satiety enhancing factor? Appetite, 56 (2), 511-515.
  12. Roy C.C., Kien C. L., Bouthillier L., Levy E., (2006). Short-Chain Fatty Acids: Ready for Prime Time? Nutrtion in Clinical Practice 21: 351-386.
  13. Smith, J.G., 1995. Molecular and genetic effects of dietary derived butyric acid. Food Technology (USA) 11, 87–90.
  14. Roediger, W.E., 1980. Role of anaerobic bacteria in the metabolic welfare of the colonic mucosa in man. Gut 21, 793–798.
  15. Coakley, M., Johnson, M.C., McGrath, E., Rahman, S., Ross, R.P., Fitzgerald, G.F., Devery, R., Stanton, C., 2006. Intestinal bifidobacteria that produce trans-9, trans-11 conjugated linoleic acid: a fatty acid with antiproliferative activity against human colon SW480 and HT-29 cancer cells. Nutrition and Cancer International Journal 56, 95–102.
  16. Belury, M., 2002. Not all trans-fatty acids are alike: what consumers may lose when we oversimplify nutrition facts. Journal of the American Dietetic Association 102, 1606–1607.
  17. Houseknecht, K.L., Heuvel, J.P., Vanden, M.-C., Silvia, Y., Portocarrero, C.P., Peck, L.W., Nickel, K.P., Belury, M.A., 1998. Dietary conjugated linoleic acid normalizes impaired glucose tolerance in the Zucker diabetic Fatty fa/fa rat. Biochemical and Biophysical Research Communications 244, 678–682.
  18. Belury, M., Kempa-Steczko, A., 1997. Conjugated linoleic acid modulates hepatic lipid composition in mice. Lipids 32, 199–204.
  19. Brownbill, R.A., Petrosian, M., Ilich, J.Z., 2005. Association between dietary conjugated linoleic acid and bone mineral density in postmenopausal women. Journal of the American College of Nutrition 24, 177–181.
  20. Kelly, O., Cashman, K.D., 2004. The effect of conjugated linoleic acid on calcium absorption and bone metabolism and composition in adult ovariectomised rats. Prostaglandins, Leukotrienes, and Essential Fatty Acids 71, 295–301.
  21. Watkins, B.A., Seifert, M.F., 2000. Conjugated linoleic acid and bone biology. Journal of the American College of Nutrition 19, 478S–486S.
  22. Butel M., Roland N., 1998. Clostridia pathogenicity in experimental necrotising enterocolitis in gnotobiotic quails and protective role of bifidobacteria. Journal of Medical Microbiology 47: 391-399.
  23. Butel M., Catala I., Waligora-Dupriet A., et al., 2001. Protective effect of dietary oligofructose against cecitis induced by clostridia in gnotobiotic quails. Microbial Ecology in Health and Disease 13: 166-172.
  24. Bomba A., Nemcova R., et al., 2002. Improvement of the prebiotic effect of micro- organisms by their combination with matlodextrins, fructo- oliogsaccharides and polyunsaturated fatty acids. British Journal of Nutrition 88: S95-S99.
  25. Oli M.W., Petschow B.W., Buddington R.K., 1998. Evaluation of fructooligosaccharide supplementation of oral electrolyte solutions for treatment of diarrhea: recovery of the intestinal bacteria. Digestive Diseases and Sciences 43: 138-147.
  26. Buddington K.K., Donahoo J.B., Buddington R.K., 2002. Dietary oligofructose and inulin protect mice from enteric and systemic pathogens and tumor inducers. Journal of Nutrition 132: 472-477.
  27. Verghese M., Walker L.T., Shackelford L. Chawan C.B., 2005. Inhibitory effects of nondigestible carbohydrates of different chain lengths on azoxymethane-induced aberrant crypt foci in Fisher 344 rats. Nutritional Research 25: 859-868.
  28. Roller M., Femia A.P., Caderni G., Rechkemmer G., Watzl B., 2004. Intestinal immunity of rats with colon cancer is modulated by oligofructose-enriched inulin combined with Lactobacillus rhamnosus and Bifidobacterium lactis. British Journal of Nutrition 92: 931-938.
  29. Ten Bruggencate S.J., Bovee-Oudenhoven I.M., Lettink-Wissink M.L., Katan M.B., Van der Meer R., 2004. Dietary fructo- oligosaccharides and inulin decrease resistance of rats to Salmonella: protective role of calcium. Gut 53: 530-535.
  30. Orrhage K., Sjostedt S., Nord C.E., 200. Effects of supplements with lactic acid bacteria. The Journal of Antimicrobial Chemotherapy 46: 603-611.
  31. Lewis S., Burmeister S., Brazier J., 2005. Effect of the prebiotic oligofructose on relapse of Clostridium difficile-associated diarrhea: a randomized, controlled study. Clinical Gastroenterology and Hepatology 3: 442-448.
  32. Furrie E., Macfarlane S., Kennedy A., 2005. Synbiotic therapy (Bifidobacterium longum/Synergy1) initiates resolution of inflammation in patients with active ulcerative colitis: a randomized controlled pilot trial. Gut 54: 242-249.
  33. Casellas F., Borruel N., Torrejon A., 2007. Oral oligofructose-enriched inulin supplementation in acute colitis is well tolerated and associated with lower faecal calprotectin. Alimentary Pharmacology & Therapeutics 25: 1061-1067.
  34. Lindsay J.O., Whelan K., Stagg A.J., et al., 2006. Clinical, microbiological and immunological effects of fructooligosaccharides in patients with Crohn’s disease. Gut 55: 348-355.
  35. Kiessling, G., Schneider, J., Jahreis, G., 2002. Long-term consumption of fermented dairy products over 6 months increases HDL cholesterol. European Journal of Clinical Nutrition 56, 843–849.
  36. Jiang, T., Mustapha, A., Savaiano, D.A., 1996. Improvement of lactose digestion in humans by ingestion of unfermented milk containing Bifidobacterium longum. Journal of Dairy Science 79, 750–757.
  37. He, T., Priebe, M.G., Zhong, Y., Huang, C., Harmsen, H.J.M., Raangs, G.C., Antoine, J.M., Welling, G.W., Vonk, R.J., 2007. Effects of yogurt and bifidobacteria supplementa- tion on the colonic microbiota in lactose-intolerant subjects. Journal of Applied Microbiology 104, 595–604.
  38. Saavedra, J.M., Bauman, N.A., Perman, J.A., Yolken, R.H., Oung, I., 1994. Feeding of Bifidobacterium bifidum and Streptococcus thermophilus to infants in hospital for prevention of diarrhoea and shedding of rotavirus. The Lancet 344, 1046–1049.
  39. Plummer, S., Weaver, M.A., Harris, J.C., Dee, P., Hunter, J., 2004. Clostridium difficile pilot study: effects of probiotic supplementation on the incidence of C. difficile diarrhoea. International Microbiology 7, 59–62.
  40. Gibson G.R., Roberfroid M.B., 1995. Dietary modulation of the human colonic microbiota: Introducing the concept of prebiotics. Journal of Nutrition 125:1401–1412.
  41. Cani P.D., Lecourt E., Dewulf E.M., et al., 2009 Gut microbiota fermentation of prebiotics increases satietogenic and incretin gut peptide production with consequences for appetite sensation and glucose response after a meal. American Journal of Clinical Nutrition 90:1236–1243.
  42. Strowski M.Z., Wiedenmann B., 2009. Probiotic carbohydrates reduce intestinal permeability and inflammation in metabolic diseases. Gut 58:1044–1045.


Comments are closed.

Post Navigation