Prebiotics: How to feed your family’s friendly gut flora

© 2009 – 2012 Gwen Dewar, Ph.D., all rights reserved

Like opens in a new windowprobiotics, prebiotics are a popular new food additive.

Should your family be consuming them?

Experiments suggest that prebiotic supplements are safe. They are probably healthful, too.

Here is an overview of the subject: What prebiotics are, where you can find them, and why you might want to make them a regular part of your diet.

What are prebiotics?

Nutrients for the probiotics colonizing your body


Think of them as food for the “friendly” bacteria in your gut.

Prebiotics are hard-to-digest food ingredients that can be metabolized by probiotics, the beneficial microorganisms living in your digestive tract (Gibson and Roberfroid 1995).

To date, most research has focused on certain oligosaccharides, in particular:

  • fructooligossacharides (FOS)
  • galactooligosaccharides (GOS)
  • inulin

These are actually carbohydrates, albeit carbs that humans can’t digest. The only energy we get from FOS, GOS, and inulin is provided by our gut flora.

Bacteria in the colon ferment the oligosaccharides, producing short-chain fatty acids, lactate, and gas. The process provides us with a bit of energy, but not much: FOS and inulin yield about 1.5 calories per gram (Niness 1999).

A variety of bacteria can metabolize the nondigestible oligosaccharides. However, two groups–the probiotic bifidobacteria and lactobacilli–seem to thrive on these prebiotics.   

In experiments where people have consumed prebiotic oligosaccharides, the composition of their gut flora changed. The numbers of bifidobacteria and lactobacilli increased at the expense of pathogenic bacteria, like E. coli (see below).

Where you’ll find prebiotic oligosaccharides


Because of their pleasant taste characteristics and low-calorie status, FOS and inulin have been added to many food products. Inulin has a creamy, fatlike texture that makes it a good fat substitute. You’ll find it in many table spreads, salad dressings, and dairy products. Oligofructose (a FOS) tastes sweet, and is about 30% as sweet as sucrose. Oligofructose has been added to some dairy products and baked goods (Niness 1999).

Natural sources

Oliosaccharides are found in breast milk, which may partly explain why breastfed babies experience fewer infections (Boehm and Moro 2008).

FOS, GOS, and inulin are also found naturally in these foods:

  • Onions
  • Garlic
  • Milk
  • Apples
  • Bananas
  • Cabbage
  • Wheat
  • Oats
  • Artichokes
  • Asparagus
  • Leeks
  • Chicory

What is the evidence in favor of consuming prebiotics?

Controlled, randomized studies suggest that lactobaccili and bifidobacteria supplements  are effective treatments for childhood diarrhea and antibiotic-induced diarrhea. Probiotic supplements may be helpful for other ailments as well.

As a result, researchers have reasoned that increasing quantities of lactobaccili and bifidobacteria already in the gut –by feeding them prebiotic oligosaccharides–would produce similar benefits (Roberfroid 2000).

There’s evidence from breast milk, too. Breast milk contains oligosaccharides. These prebiotics stimulate the growth of beneficial bifidobacteria in the gut, and may explain why breastfed babies suffer fewer infections than do formula-fed babies.

So the question is: Do prebiotics supplements really produce the desired changes in gut flora? Researchers attempt to answer the question by feeding people prebiotics and then analyzing their stools.

Randomized, controlled experiments on adults have demonstrated that prebiotics supplements increase the proportion of “good” bifidobacteria in stools (e.g., Depeint et al 2008; Kolida et al 2007).

Studies of formula-fed babies have yielded similar results.

Testing fortified baby formula

In one randomized, double-blind study, formula-fed newborns were given one of two treatments.

  • Feedings with prebiotic-fortified baby formula (0.4 g/100 ml prebiotic galacto- and long-chain fructooligosaccharides)
  • Feedings with standard baby formula

Researchers monitored the babies for 12 weeks. Both groups experienced similar growth rates. However, the oligosaccharide-treated babies had fewer diarrhea-causing bacteria in their stools (Costalos et al 2008).

Another, similar experiment found that babies receiving fructooligosaccharides in their formula had more bifidobacteria in their stool and fewer E.coli (Kapiki et al 2007).

And an earlier experiment compared the stools of infants who’d received fortified baby formula with the stools of breastfed babies (Knol et al 2005).

In this case, some babies were given formula with .8 g/100 ml GOS/FOS in a ratio of 9:1. Compared with babies given standard formula, the treated babies produced stools that contained more bifidobacteria and waste products associated with breastfed babies. The results have been replicated since then (Holsher et al 2012).

These are just a few examples. Not every study has reported statistically significant results. But the weight of the evidence seems to favor the use of prebiotics.

As Günther Boehm and Guido Moro conclude

“The data clearly demonstrate that prebiotics of nonmilk origin can mimic the prebiotic effect of breast-feeding, and this has positive consequences for the postnatal development of the immune system” (Boehm and Moro 2008).

Other benefits

In addition to stimulating the growth of probiotics, oligofructose and inulin have other benefits. For example:

  • Nondigestible oligosaccharides behave like dietary fiber, and may confer some of the benefits of fiber (Roberfroid 1993).
  • Nondigestable oligosaccharides appear to help the body absorb calcium and magnesium (Elia and Cummings 2007).
  • Unlike probiotics, prebiotics are easy to use. Probiotics are living organisms. For probiotic supplements to work, you must insure that the probiotics are still viable. By contrast, prebiotics are carbohydrates. They can be cooked or frozen without damaging their healthful properties (Gibson and Rastall 2004).

In addition, prebiotics might help probiotics “take hold.” Researchers suspect that probiotics may be more effective when combined with prebiotics (Kaur et al 2009).

But watch the dose…

Nondigestible oligosaccharides are widely accepted as safe food additives. But to achieve any prebiotic effects, people need to consume at least 5 grams a day.

How much is too much? Experiments suggest that adults can consume up to 30 grams a day without side effects. Higher doses are associated with gas and intestinal discomfort. Doses exceeding 30 grams / day might also benefit the bad bacteria living in your intestinal tract (Gibson and Rastall 2004).

More information

You can read more about probiotics in this evidence-based article,  opens in a new window“Probiotics for kids with diarrhea and other ailments: Scientific evidence”

For a conceptual overview of prebiotics, check out Glenn Gibson’s and Marcel Roberfroid’s influential review paper for the Journal of Nutrition,  opens in a new window“Dietary modulation of the human colonic microbiota: Introducing the concept of probiotics”

References: Prebiotics

Boehm G and Moro G. 2008. opens in a new windowStructural and functional aspects of prebiotics used in infant nutrition. J Nutr. 138(9):1818S-1828S.

Costalos C, Kapiki A, Apostolou M, Papathoma E. 2008. The effect of a prebiotic supplemented formula on growth and stool microbiology of term infants. Early Hum Dev. 84(1):45-9.

Depeint F, Tzortzis G, Vulevic J, I’anson K, and Gibson GR. 2008. Prebiotic evaluation of a novel galactooligosaccharide mixture produced by the enzymatic activity of Bifidobacterium bifidum NCIMB 41171, in healthy humans: a randomized, double-blind, crossover, placebo-controlled intervention study. Am J Clin Nutr. 87(3):785-91.

Elia M and Cummings JH. 2007. Physiological aspects of energy metabolism and gastrointestinal effects of carbohydrates. Eur J Clin Nutr. 61 Suppl 1:S40-74.

Gibson GR, McCartney AL, and Rastall RA. 2005. Prebiotics and resistance to gastrointestinal infections. Br J Nutr. 93 Suppl 1:S31-4.

Gibson GR and Rastall RA. 2004. When we eat, which bacteria should we be feeding? ASM news 70(5): 224-231.

Gibson GR and Roberfroid MB. 1995. Dietary modulation of the human colonic microbiota: Introducing the concept of prebiotics. Journal of Nutrition 1401-1412.

Holscher HD, Faust KL, Czerkies LA, Litov R, Ziegler EE, Lessin H, Hatch T, Sun S, and Tappenden KA. 2012. Effects of prebiotic-containing infant formula on gastrointestinal tolerance and fecal microbiota in a randomized controlled trial.JPEN J Parenter Enteral Nutr. 36(1 Suppl):95S-105S.

Kaur IP, Kuhad A, Garg A, and Chopra K. 2009. Probiotics: delineation of prophylactic and therapeutic benefits. J Med Food. 12(2):219-35.

Kolida S, Meyer D, and Gibson GR. A double-blind placebo-controlled study to establish the bifidogenic dose of inulin in healthy humans. Eur J Clin Nutr. 61(10):1189-95.

Niness KR. 1999. Inulin and oligofructose: What are they? Journal of Nutrition. 129:1402S-1406S

Scholz-Ahrens KE , Schaafsma G, Heuvel E, and Schrezenmeir J. 2001. Effects of prebiotics on mineral metabolism. Am J Clin Nutr. 73(suppl):459S-464S.

Content last modified 3/12

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