How Prebiotics Work

by Tanya Zilberter, PhD

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GO-diet I The PRE-biotic Inulin I Functional Foods I Probiotics

Living in our intestines, are a number of species: some are friendly (e.g., bifidobacterium, eubacterium and lactobacillus); some are hostile (e.g., clostridium, shigella, and veillonella); and some might be deadly.

A prebiotic (not probiotic) is "a non-digestible food ingredient that beneficially affects the host [you] by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon." (Am Clin Nutrit, 2001; 73:406S-409S.)

A probiotic brings external friendly bacteria into the gut's ecosystem, while a prebiotic stimulates the growth the potentially health-promoting microbes-insiders, thus modulating the composition of the natural ecosystem.

Inulin

The best (and, some researchers believe, the only) example of a prebiotic is inulin. Inulin is a "non-digestible oligosaccharide," which simply means that it is a carbohydrate that can not be digested. It can be - and is being - fermented in the lower parts of the intestinal tract. As a result, the friendly intestinal microflora (bifidobacterium) grows better. (How we benefit from that friendly flora is another question and we'll discuss it next time; sign up to be notified.)

Inulin occurs naturally in large quantities in some of the most famous herbs, such as burdock root, dandelion root, elecampane root and chicory root. It is soluble only in hot water, which is why it traditionally been ingested in hot teas. It has a mildly sweet taste and is filling, but, because it is not absorbed, it does not affect blood-sugar levels.

The directly registered effects of the prebiotic inulin are -

• improved bowel functions mainly due to the increase of fecal bulk;
• improved bioavailability of minerals that, among other things, may contribute to a reduction in the risk of osteoporosis;
• improved fat metabolism: there is preliminary evidence of a triglyceride-reducing effect of inulin; and

• possible reduction of the risk of colon cancer. A "synbiotic" approach combining inulin and bifidobacteria was shown to be more effective than either the probiotic or the prebiotic alone.

Warning! Inulin can trigger an allergic reaction!

Sources:

J Nutr 1999;127(suppl):S1398-401

Annu Rev Nutr 1998;18:117-43

Am J Clin Nutr 2001;73:456S-8S

Am J Clin Nutr 2001; 73:459S -64

Br J Nutr 1999; 82:23-30

Carcinogenesis 1997; 18:1371-4