Like probiotics, 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.
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:
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).
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:
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.
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).
In addition to stimulating the growth of probiotics, oligofructose and inulin have other benefits. For example:
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).
You can read more about probiotics in this evidence-based article, "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, "Dietary modulation of the human colonic microbiota: Introducing the concept of probiotics"
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