Research Review: Busting belly bugs with bacteria | Precision Nutrition

Research Review: Busting belly bugs with bacteria

By Helen Kollias


Chances are that you’ve seen those yogurt commercials with the “14 day challenge” involving belly-dancing midsections, cartoony yellow bubbles that presumably represent tiny happy faces in your tummy, and Jamie Lee Curtis oversharing digestive issues with coworkers and friends.

But thanks to the new probiotic yogurt, in only 14 days your innards will be happier and you won’t need that copy of War and Peace to read when you go to the bathroom. Hooray! Now that’s something to discuss with Suzy in Accounting!

In the last five years or so there has been a boom in the marketing of the new it food or more accurately the new it supplement — probiotics.

Yes, the people on TV tell you that probiotics are fantastic, but do you really know what probiotics are and why you even need them?

There’s a party in your tummy

Before I get into probiotics you need to know a little about bacteria, the active ingredient in probiotics. (I guess calling it “probiotics” is easier to sell than “billions of tiny wiggling micro-organisms that live in your tummy”.)

This may gross you out a bit, but let’s persevere in the name of science: You have bacteria on your body. A lot. All over.

In fact, you have bacteria anywhere your body is in contact with the outside world: on your skin, in your mouth, in your respiratory tract, in your mouth, in your gut (gastrointestinal tract), your rectum and your urinogenital tract.

Why does your body keep these little animals around? They protect you and your body from other bacteria (as well as other micro-organisms like yeast and viruses).

If you want to read more about what your bacteria do in your gut, check out Say Hello to (My Trillions of) Little Friends: Gut Bacteria and Your Metabolism. In this article, I explain what your good bacteria in your gut (intestine) do for you. Also, check out Bryan Walsh’s Fix Your Gut, Fix Your Health.

Take a moment and thank all your bacteria for their hard work… I’ll wait. (You might want to give them a collective shout-out via the PA system instead of shaking all their teeny hands.)

probiotics 0987


Even though you have a lot of bacteria hanging out with you, not all bacteria is good bacteria. Basically, there is bacteria you want in your gut (good bacteria) and bacteria you don’t want in your gut (bad bacteria).

Good bacteria in your gut do things like:

  • help you absorb nutrients (e.g. by breaking down oligosaccharides)
  • regulate gas and acid balance
  • produce vitamins (K & B)
  • produce amino acids.

Things like infection, antibiotics, hormones, radiation, change in diet, and stress tend to bump off the good bacteria in your gut.

Because we always have bacteria in our GI tracts, and because bacteria compete for territory, a decrease in good guys can mean an increase in bad guys.

What are probiotics?

The World Health Organization and the Food and Agriculture Organization of the United Nations define probiotics (from the Greek “pro”, or “in favour of” and “bios”, or “life” — thus, “life-favouring”) as “live micro-organisms, which, when administered in adequate amounts, confer a health benefit on the host.” In other words, good bacteria.

There are a bunch of different bacteria (and other micro-oorganims) that are used as probiotics, but most come from one of two bacterial families, Lactobacilli and Bifidobacteria [1].

What do probiotics do?

Nobody knows what exactly probiotics do but there are a few ideas [2]:

  • Probiotics provide good bacteria to either push bad bacteria out of the gut or prevent them getting a foothold in the first place
  • The good bacteria in the probiotics help in making an intestinal barrier (I call this the “Red Rover” idea)
  • Probiotics can help the immune system

Chances are probiotics works in more than one way and that all three of these ideas turn out to be true.

Good luck getting through these good bacteria!
Good luck getting through these good bacteria!

Research question

In this week’s review I take a look at an article that tries to figure out how probiotics work and if they work for diseases such as Crohn’s, which cause inflammation of the gastrointestinal tract.

Pagnini C, Saeed R, Bamias G, Arseneau KO, Pizarro TT, Cominelli F. Probiotics promote gut health through stimulation of epithelial innate immunity. Proc Natl Acad Sci U S A. 2010 Jan 5;107(1):454-9.


Since it’s really really hard to find people without any bacteria in their gut already, the scientists had to use mice in this study that were born and raised without being exposed to any bacteria, viruses, etc (think Bubble Boy).

These bacteria-free mice were also genetically designed to have Crohn’s-like intestinal inflammation (these mice are called SAMP1/YitFc).

In the study, the mice got the probiotic for 6 weeks either before they started having symptoms of intestinal inflammation (3 weeks old) or after (30 weeks old).

The probiotic had a bunch of bacteria:

  • Bifidobacterium breve
  • Bifidobacterium longum
  • Bifidobacterium infantis
  • Lactobacillus acidophilus
  • Lactobacillus plantarum
  • Lactobacillus paracasei
  • Lactobacillus bulgaricus
  • Streptococcus thermophilus

And when I say “a bunch”, I mean 5×109 CFUs (colony forming units – think of this as a unit of measure like a teaspoon). When you look for a probiotic supplement, check to see whether the CFUs are listed on the package.


Taking a 5×109 CFU dose of the probiotic prevented intestinal inflammation in mice if they got the probiotic before they started having symptoms. However, the probiotic didn’t help once the mice already had intestinal inflammation.

How did the probiotics work?

The bacteria from the probiotic work in a couple of ways:

  • They restore the protective barrier of the intestinal lining, aka the epithelium (the Red Rover idea)
  • They boost the immune system by getting the cells to make more tumor necrosis factor, TNF-alpha.

The researchers also wanted to know: Do the good bacteria actively change the other bacteria and microorganisms in the gut (thus crowding out other bacteria)? Or were the good bacteria anti-inflammatory?

Turns out the probiotics were only passing through. However, the good bacteria actively triggered an anti-inflammatory response in the lining of the intestine.

Do probiotics make it to our guts?

One important question that the researchers wanted to answer: Do probiotics actually get to the GI tract?

This isn’t a stupid question — our acid-bath stomachs are pretty good at terminating bacteria with extreme prejudice. Just because there are bacteria in the gut doesn’t mean that they’re the right ones.

As it turns out, the answer is yes: Genetic testing of the intestinal bacteria showed that the little guys survived their fantastic voyage through Mr. Mouse Tummy.


As the saying goes, “An ounce of prevention is worth a pound of cure.” Taking a high dosage of probiotics prevented, but didn’t cure, genetically predisposed Crohn’s-like intestinal inflammation.

The best time to take probiotics is before you have a digestive problem, instead of after — especially in the case of inflammatory diseases like Crohn’s disease.

You can take probiotics as a supplement, or you can look for foods containing beneficial bacteria, such as yogurt, kefir, or naturally fermented foods like raw sauerkraut and kimchi.


Click here to view the information sources referenced in this article.

Learn more

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