Thursday, October 29, 2009

Prebiotics, Synbiotics and the Immune System

Bananas contain a small amount of prebiotics.
Bananas contain a small amount of prebiotics. (Photo by clairity)

Last week I wrote about the effectiveness of probiotics for improving gut health and immunity. While not all studies agreed they could ward off the flu, pretty much all of them found at least some positive effects on the immune system from taking probiotics.

As mentioned, probiotics are available as supplements and in some foods such as dairy products. But there's also another way of promoting healthy bacteria in the gastrointestinal tract: prebiotics. Prebiotics are non-digestible ingredients in food that stimulate the growth and activity of healthy bacteria inside the body. In a sense, prebiotics cause the body to produce its own probiotics.

What are prebiotics?

There is some disagreement in the scientific community over which substances are probiotics, but at the minimum this category includes oligofructose and inulin. Oligofructose is a fructooligosaccharide, which refers to a short chain of sugar (in this case fructose) molecules. Inulins are a group of polysaccharides, which means a long chain of sugar molecules.

Since these prebiotics are composed of sugars, they are carbohydrates, and since they are indigestable, they are fibers. Further, inulin and oligofructose are soluble fibers, meaning that they're able to dissolve in water. Though they can't be digested, they do undergo fermentation as the bacteria get their hands on them. At the same time, the microflora of the gut is affected.

As the bacteria metabolise prebiotics in the colon, significant quantities of carbon dioxide, hydrogen and methane are released, which means that eating foods with prebiotics can cause gas. With long-term consumption, as the body grows accustomed to inulin and oligofructose, this unpleasant side effect is reduced.

Food sources of prebiotics

Inulin and oligofructose are naturally present in many plant foods, but their quantities differ significantly. Here's a list of foods in decreasing order of their average prebiotic content (values per 100 g [link]):

  • Chicory root: 41.6 g inulin, 22.9 g oligofructose
  • Jerusalem artichoke: 18.0 g inulin, 13.5 g oligofructose
  • Dandelion greens: 13.5 g inulin, 10.8 g oligofructose
  • Garlic: 12.5 g inulin, 5.0 g oligofructose
  • Leek: 6.5 g inulin, 5.2 g oligofructose
  • Asparagus: 2.5 g inulin, 2.5 g oligofructose
  • Wheat bran: 2.5 g inulin, 2.5 g oligofructose
  • Wheat flour, baked: 2.4 g inulin, 2.4 g oligofructose
  • Banana: 0.5 g inulin, 0.5 oligofructose

Note that unless stated otherwise, these figures apply to raw foods. Cooking in general seems to reduce content of prebiotics by 25-75%. Chicory root and Jerusalem artichoke (not to be confused with the globe artichoke, which is green in color) clearly take the cake. Even when cooked, these two plants still contain plenty of inulin and oligofructose.

Prebiotics and the immune system

Since probiotics have been shown to benefit the immune system, and prebiotics promote probiotic bacteria in the gastrointestinal tract, it makes sense that the consumption of prebiotics would have similar effects. Unfortunately, for those interested in preventing the common cold and other viral infections, not many studies have actually looked at whether prebiotics are effective. With that in mind, let's take a look at the evidence behind prebiotics and their effect on immune health in general.

There are some studies on humans showing that the consumption of prebiotics does modify the immune system (link, link). Specifically, prebiotics may reduce intestinal infections and intenstinal inflammation. On the other hand, inulin and oligofructose can also activate immune cells and increase the cytotoxicity of natural killer cells and the production of cytokines (link). In rats, prebiotics increase the number of T cells, interleukin-2 and interleukin-4, which indicates that prebiotics enhance the immune system (link).

One study found that a prebiotic galacto-oligosaccharide mixture was helpful in reducing travellers' diarrhoea (link). Those who got the prebiotic instead of the placebo had fewer incidences and less symptoms of diarrhoea when travelling to foreign countires. In infants, human milk protects from morbidity and mortality due to diarrhoea compared to formula milk, most likely because of the presence of prebiotic oligosaccharides in human milk (link). Some studies have also shown that prebiotics may help with irritable bowel syndrome (link), but the evidence is inconclusive. And, even though prebiotics may cause gas, they can also help with lactose intolerance (link).

A commonly cited example of the health effects of probiotic-containing foods is their anticarcinogenic activity. This is at least in part due to the stimulation of lactic acid producing bacteria in the colon, since lactic acid producing bacteria reduce the ability of microflora to produce carcinogens. Prebiotics seem to have a similar effect (link), possibly being even more effective than probiotics (link).

As for influenza, one study found that gamma-inulin, the active component of inulin preparations, improved the response to a variety of antigens in mice (link). When given a lethal dose of the influenza virus, all of the mice died, but when gamma-inulin was administered at the same time, half of them survived.

Synbiotics: even better than prebiotics and probiotics?

Synbiotics is the fancy name given to combinations of probiotics and prebiotics. The idea is that these two would work synergistically to produce even better results than either one would alone. Indeed, there is some evidence that synbiotics are superior to prebiotics and probiotics (link). In any case, the effect of synbiotics is different from that of pre- or probiotics (link).

Not all the studies are quite as promising, however One study found that rats fed prebiotics actually had a poorer resistance to salmonella than controls (link). This impairment was partially but not entirely prevented by calcium phosphate. It's not clear whether the same applies to humans, but it does emphasize the fact that we don't entirely understand how synbiotics affect the immune system.


While almost all studies have shown at least some benefit from probiotics, less is known about the effect of probiotics and synbiotics on the immune system. Prebiotics appear to increase the number and activity of probiotic bacteria in the body, but studies in humans and animals have yielded inconclusive results.

Sources of prebiotics, namely inulin and fructooligosaccharide, include nutritional supplements and plant foods. Compared to most commonly consumed foods with prebiotics, such as wheat and banana, supplements are often a better source. However, Jerusalem artichoke and chicory root are the best sources of inulin and fructooligosaccharide, containing much more than any supplement.

For more information on immunity and supplements, see these posts:

Enhancing Immunity with Probiotics: Can They Ward Off the Flu?
Swine Flu and Avoiding the Cytokine Storm: What to Eat and What Not to Eat?
Examining Possible Causes for Slower Wound Healing
How to Choose Between Different Forms of Coenzyme Q10: Ubiquinone vs. Ubiquinol

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9 kommenttia:

Kris & Andrea October 30, 2009 at 7:12 AM  

Fantastic post, thanks!

Interesting note: while prebiotics are technically carbohydrates, they are not included under the 'carb' content on nutrition labeling. It may sound odd, but this is accurate: because they are not digested or absorbed, the 'carb' content of the carbohydrates is effectively zero! Amazing stuff.

We make a prebiotic supplement called Prebiotin and we nearly had a fight with our label printer over this: They just couldn't believe that "carbs" were not to be listed as "carbs" on the dietary info label!

Synaura November 11, 2009 at 11:48 AM  

Body detoxification is important in order to maximize our energy and to avoid frequent illness, fatigues, pains, depression and loss of concentration.
The Right Place. The Right Time

Chet June 24, 2010 at 7:04 PM  

Great post. I'm going to add dandelion greens to my salad from now on.

Anonymous August 20, 2011 at 11:21 AM  

Lalonde has come out against inulin and I believe chicory

gwarm September 8, 2011 at 1:19 AM  

Some of these ancestral, paleo bloggers are posting information saying low-carb is not the ideal:
Saw this on (links huntgatherlove MelissaMcEwen blogpost, which links to PDF dissertation: "Most microorganisms in the colon prefer to ferment
carbohydrates and switch to protein fermentation when fermentable carbohydrates
are depleted.19 While carbohydrate fermentation generally leads to healthpromoting
SCFA production, protein fermentation yields branched-chain fatty acids
and potentially toxic metabolites (e.g. ammonia, amines, N-nitroso compounds,
phenols, indoles and thiols).20")
(Checkout huntgatherlove's AHS speech on gut bacteria: - video
And of course Stephan Guyenet on butyrate:
"In most animals, the highest concentration of butyrate is found in the gut. That's because it's produced by intestinal bacteria from carbohydrate that the host cannot digest, such as cellulose and pectin. Indigestible carbohydrate is the main form of dietary fiber.

It turns out, butyrate has been around in the mammalian gut for so long that the lining of our large intestine has evolved to use it as its primary source of energy. It does more than just feed the bowel, however. It also has potent anti-inflammatory and anti-cancer effects.

Butyrate, and other short-chain fatty acids produced by gut bacteria**, has a remarkable effect on intestinal permeability. In tissue culture and live rats, short-chain fatty acids cause a large and rapid decrease in intestinal permeability. Butyrate, or dietary fiber, prevents the loss of intestinal premeability in rat models of ulcerative colitis. This shows that short-chain fatty acids, including butyrate, play an important role in the maintenance of gut barrier integrity. Impaired gut barrier integrity is associated with many diseases, including fatty liver, heart failure and autoimmune diseases (thanks to Pedro Bastos for this information-- I'll be covering the topic in more detail later).

Butyrate's role doesn't end in the gut. It's absorbed into the circulation, and may exert effects on the rest of the body as well. In human blood immune cells, butyrate is potently anti-inflammatory***.
Whole plant foods such as sweet potatoes, properly prepared whole grains, beans, vegetables, fruit and nuts are good sources of fiber. "

JLL September 8, 2011 at 8:49 PM  


I'm not sure low-carb is ideal either; I just think it's the easiest and quickest way for most overweight people to lose weight. When you're already thin, it's a different question. I used to be very anti-carbs, but following the debate of the past few years has made me change my position somewhat.

Still, I wouldn't start eating grains just because they have fiber. I'd rather eat sweet potatoes.


Catherine Milne October 9, 2011 at 12:35 PM  

good post, but in two places you've put 'probiotics' instead of 'prebiotics'.

gwarm October 31, 2011 at 3:52 PM  

From DrGreger’s PDFs re: AGEs and microflora:

may oxidise to dicarbonyls, e.g. glyoxal and methylglyoxal
which are particularly reactive towards arginine residues in
protein to form hydroimidazolones. When a reducing sugar
reacts with the epsilon amino group of lysine, a reaction
intermediate, known as an Amadori rearrangement product
(ARP) is formed. ARPs are pre-AGEs and when the initial
reducing sugar is glucose, the ARP is known as fructoselysine
(FL). ARPs are unstable reaction intermediates that
degrade to AGEs, including those reported to be the most
abundant representatives in food, i.e. Ne-(carboxymethyl)-
lysine (CML) and pyrraline [2]. AGEs comprise a diverse
group of compounds and the structures of l20 have been
elucidated to date. So far, most research on AGEs have
been directed to their effects in vivo, where they are associated
with the complications of diabetes, especially renal,
retinal and cardiovascular disease [3].”

“Up to 80% of dietary ARPs are not absorbed but are
degraded by the gut microflora.” PDF linked here:

Anonymous June 19, 2014 at 7:40 AM  

Haven't seen a post for a while. Right on the money! Antibiotics(against life) will kill you or at least cause irreparable damage to the immune system. Which can take months are even years to repair if you're a fairly healthy eater. I have repaired myself for years. Thanks to probiotics, high level plant compounds and minerals.,
Great information on the synbiotic effect follows my own inhuman experience. Thanks, 7AR

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