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 or Bifidobacterium (bifidobacteria) 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 of FOS inulin you ingest as you heal your gut.
The following has been briefly covered in my post “The many vital functions of healthy gut flora” but this is a more in-depth coverage of the subject.
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 received 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 substances 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 of utilizing butyrate properly could be a predisposing factor in ulcerative colitis. (14)
Prebiotics and Conjugated Linoleic Acid
Bifidobacterium was first reported as also 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 reducing weight gain, and having anti-diabetic, anti-carcinogenic and anti-atherosclerotic properties. (16)
In the pre-diabetic Zucker fatty rat, CLA was shown to normalize glucose levels. (17) CLA has also been shown to regulate the leptin hormone in 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 babies, 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. For a couple of prebiotic recommendations, click here.
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- 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.
- 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.
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- 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.
- Arora, T., Sharma, R, Frost, G., 2011. Propionate. Anti-obesity and satiety enhancing factor? Appetite, 56 (2), 511-515.
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