Research Review: Good bacteria, gut health and exercise | Precision Nutrition

Research Review:
Good bacteria, gut health and exercise

By Jennifer Koslo


Our digestive systems are home to hundreds of different bacterial species that keep our intestinal linings healthy, break down food, and regulate our immune response.

Evidence suggests that by controlling the immune response, supplemental probiotics can help prevent and treat diarrhea and decrease inflammation caused by diet and stress — whether from life or exercise.

But can probiotics also reduce GI damage, symptoms, and illness caused by intense exercise?


Is your belly in balance or do you suffer from CPBBS (caca-poopy-blocked-up-bowel syndrome)?

Okay so maybe CPBBS isn’t exactly an official term for GI disturbances, but more than likely you or someone you know suffers from occasional “plumbing problems” ranging from gas and bloating to nausea, stomach cramps, constipation or diarrhea.

Not surprisingly, diet and lifestyle play a key role in keeping our intestines running smoothly. Common culprits that can wreak havoc on our GI tracts:

  • not eating enough fruit, vegetables, and/or dietary fiber in general;
  • food intolerances (such as a gluten or dairy intolerance);
  • taking antibiotics; and/or
  • a stressful lifestyle (which can include stress from anything — life events, relationships, finances, travel, even intense regular exercise).

That last point may surprise you a little. Yes, exercise is good for you. But high-performance athletes, especially endurance athletes, suffer a lot of GI complaints.

Exercise shunts blood to the muscles, away from the GI tract, and raises our core temperature. Less blood to internal organs and an increased internal temperature can disrupt the intestinal lining, setting off the inflammatory response. High training loads — training hard for several hours a week — creates a chronic stress from which the body struggles to recover.

And before you know it, you’re sick with a respiratory infection or some other illness (1).

Hmmm. Maybe it’s not such a great idea to work out to the point of puking, after all.

Our intestinal ecosystem

From birth, our gut is populated with about 1000 known species of microorganisms — and we’re discovering more all the time. This microbial ecosystem is so complex that it is considered to be a virtual organ system essential to the maintenance of our health!

How do these microscopic super-hero bugs keep us in balance?

Let’s go back to biology class for a review. The good bacteria, aka probiotics, interact with the cells of our intestinal lining and affect our immune cells. When the good bugs outnumber the “bad” bugs, or toxins, the result is a smoothly functioning digestive system and less overall inflammation.

Our gut microbiota can be altered by things like:

  • genetics;
  • the overall state of our immune system (i.e. whether there is another disease present like celiac or allergies);
  • diet;
  • exercise; and
  • stress.

We all host similar species of beneficial bacteria, but how much and which type can vary greatly, depending on the factors above, and they can also vary over time (1, 2, 3).

For example, let’s say you come down with pneumonia. When you take antibiotics, these drugs kill the good and the bad bacteria. Ridding you of your illness thus becomes a catch-22.

Most likely you’ve heard that after taking antibiotics you need to repopulate your intestines with good bacteria to keep from getting sick again and put balance back into your intestinal ecosystem.

The GI barrier and GI permeability

Scientists think that there are several reasons that probiotics work. Here are a couple of important ones.

Decreased inflammation

First, probiotics help decrease inflammation.

Generally, we don’t want inflammation in the body because it can cause our proteins to lose function and can damage the lipids (aka fats) in our cell membranes, creating free radicals. Too many free radicals result in an increase risk of illness and disease (1, 3, 4).

Tight junctions

Probiotics also affect the “tight junctions” between our intestinal cells.

Tight Junctions – sounds like a good name for a band, doesn’t it? But really, tight junctions are barriers that seal the space between the tissues lining our internal surfaces (epithelial cells). They “glue” intestinal cells together and regulate the flow of large molecules between the bloodstream and the inside of the intestine (the intestinal lumen).

Celiac disease is an example of what can happen when these junctions are compromised. Undigested gluten fragments seep into the underlying tissue, setting off an immune response.

Tight junctions are composed of more than 50 proteins. They seem to hold the key to intestinal barrier function. The expression of these proteins is influenced by dietary components like polyphenols—the antioxidant compounds found in foods like legumes, berries and chocolate – and it is also influenced by a number of probiotic strains.

"Tight junctions" in the intestinal epithelium
“Tight junctions” in the intestinal epithelium

The athlete, GI health, and probiotics

While manufacturers of popular yogurts and probiotic drinks may try to persuade you that their product holds the key to your intestinal health, not all probiotics are created equal. Nor do they have the same function.

For example, some strains like Saccharomyces boulardii may help with diarrhea, while strains of Lactobillus and Bifidobacterium have been shown to have beneficial effects on tight junctions and intestinal barrier function (5). Interestingly, certain strains of probiotics have also been shown to play a role in the development of obesity and type 2 diabetes (2).

Sadly, there are a good many other species found in foods that simply don’t survive digestion and won’t make it intact to your GI tract. So supplementing with those could be a total waste.

While taking probiotics is an area that is being researched for ailments ranging from irritable bowel and ulcerative colitis to allergies and diarrhea, there is little research in the context of sports and exercise. But wouldn’t you like to know if adding a daily dose of good bugs to your routine would make you an even healthier athlete? I know I sure would!

Research question

This week’s research review explored the effects of probiotic supplementation on intestinal permeability in male endurance athletes. The question:

Does probiotic supplementation affect markers of oxidation and inflammation in plasma, before and after intense exercise?

Lamprecht, M., Bogner, S., Schipper, G., Steinbauer, K., Fankhauser, F., Hallstrom, S., Schuetz, B., Greilberger, J.F. Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial. J Int Soc Sports Nutr 9:45, September 20, 2012.


This study used a randomized, double-blinded, placebo-controlled design, which means that the subjects were randomly assigned to either the experimental group or to the control group The experimental group took a probiotic supplement; the controls took a placebo supplement.

Because the study was double-blinded neither the researchers nor the subjects knew who was receiving what.

At this point you might be wondering who in the study actually knew what was going on. Fortunately, in double-blinded studies the treatments are usually coded so that at the end of the study the researchers can find out which subjects belonged to which group.

At baseline and at the end of the 14 week study all subjects completed 90 minutes of intense exercise.

While it wasn’t clear why 3.5 months (14 weeks) was chosen as the treatment time, most likely it was due to study feasibility along with the fact that 14 weeks should be ample time for the probiotics to have an effect. While there is no science behind it, anecdotal evidence seems to suggest that probiotics can have an effect in as little as a few days.

At baseline and at the end of the study, the subjects’ poop and blood was collected and tested.

Yeah, fun.


This study used 23 endurance-trained men (triathletes, runners, cyclists) each of whom were:

  • 30-45 years old;
  • had a VO2max greater than 45 ml/kg/min (which is considered to be good to excellent for this age group according to normative data (6);
  • had less than 20% body fat;
  • didn’t smoke; and
  • didn’t take dietary supplements within four weeks of the start of the study.

Experimental protocol

The 23 men were randomized into blocks of 6, with 11 subjects in the probiotic group and 12 in the placebo group. The researchers wanted to ensure that there was a balanced distribution of VO2max between the groups so they stratified the participants using rank statistics.

In plain English: ranking is a relationship between a set of data (in this case VO2max) that “ranks” values as either higher than, lower than or equal to the second. Why do this? In statistics it makes it easier to evaluate complex information without relying on a particular characteristic.

On the morning of the first exercise test, everyone received the same pretty substantial breakfast of just over 1000 calories, 3 hours beforehand. It was high carb (60%), moderate fat (27%) and moderate protein (13%) – a  good breakfast for a pre-workout meal – and while high in calories, the subjects needed the fuel for the intense exercise test that was to follow.

Dietary and lifestyle assessment

Before the first triple step test the men completed a 7-day food diary that was then analyzed. This food diary provided the “menu” that the subjects would subsequently follow — to ensure that nothing changed in their regular routines.

The subjects were then given copies of their 7-day food diary records and asked to duplicate this diet exactly for the 7 days leading up to the second triple step test at the end of the study. On both testing days, the subjects ate the standardized breakfast as described above.


Both groups received sachets, which either contained probiotics (experimental group) or a placebo composed of a cornstarch maltodextrin matrix (control group).

The strains contained in the sachets of the experimental group included those you would find on most common priobiotic supplements including Bifidobacterium bifidum W23 and Lactobacillus acidophilus W22. The brand name of the supplemented used was OMNi-BiOTiC®POWER.The minimum concentration of probiotics was 2.5 x 109 colony forming units (CFU) per gram.

Both groups were instructed to take 2 sachets for a total of 4 grams per day, which was equivalent to 1010 CFU per day.

So how does this dosage compare to OTC probiotic supplements? The one in my fridge has 12 billion cells per serving compared to 2 billion in the study.

Exercise tests

For 3 days before each exercise test, the subjects were told not to perform physical training. First they had to undergo eligibility testing by completing an incremental step test to exhaustion on a cycle ergometer.

During the test, an electrocardiogram, oxygen uptake, carbon dioxide, breathing rate and heart rate were recorded. Subjects wore a face mask for the collection of the gases. The actual exercise test in the experiment used a similar protocol, but repeated the incremental test twice more for a total of three step tests to voluntary exhaustion.

The entire test lasted between 80 to 90 minutes, depending on how long it took the subjects to reach exhaustion during each of the 3 steps. They had 15 minutes between intervals and were allowed to remove their face mask to drink some water.

Well, now we know why the subjects ate the 1000-calorie breakfast. Talk about a workout! This same procedure was used for testing at the end of the study at 14 weeks.

Blood and feces collection

Researchers collected blood pre-exercise and within 10 minutes post-exercise. They also needed to collect some of the subjects’ poop. They did this at baseline and at 14 weeks.

Blood chemistry panel

The subjects also had blood drawn after an overnight fast so that standard blood chemistry values could be determined.


Researchers collected several different types of measures, to get a broad picture of what was happening to the subjects. Most of the indicators focused on measuring inflammation and GI health (for instance, the integrity of the intestinal barrier).

Measure 1 Description
Triple cycle step test ergometry Measurement of VO2max, VO2max related to body weight, maximum performance and performance related to body weight were assessed in each group in each of the tests.
Zonulin Zonulin is a protein that is released from liver and intestinal epithelial cells. It plays a key role in controlling intercellular tight junctions. Measuring zonulin is one way to measure gut permeability. Increased zonulin is a marker of gut leakage.
α 1-antitrypsin This is another measure related to the integrity of the GI barrier, which estimates protein leakage into the intestinal tract.
Carbonyl groups on proteins (CP) This is a measure of protein oxidation and when elevated can result in a loss of enzyme and protein structure and function. Chronic exercise can elevate CP.
Malondialdehyde (MDA) This is a marker used to estimate lipid peroxidation. Lipid peroxidation sets off a chain reaction that can result in tissue damage and can lead to the initiation of disease.
Total oxidation status (TOS) This represents the amount of total lipid peroxides, an indicator of lipid peroxidation throughout the body.
Tumor necrosis factor alpha (TNF-α) This is a pro-inflammatory cytokine (signaling molecule) and central mediator of systemic inflammatory response.
Interleukin 6 (IL-6) This is a cytokine that originates in skeletal muscle and is known to increase with strenuous exercise.


In this study, the researchers asked two key questions:

  • How does 14 weeks of probiotic supplementation affect surrogate markers of intestinal barrier function, including intestinal permeability?
  • How does probiotic supplementation and a given exercise protocol affect markers of inflammation and oxidative stress?

What they found: Probiotic supplementation improves intestinal barrier function and reduces inflammation in trained male endurance athletes.

Here’s what they found for each indicator.

Measure Description
Triple cycle step test ergometry No significant differences between probiotic supplementation or placebo for the performance measures taken during the exercise test. Probiotics didn’t affect VO2max, which was not surprising.
Zonulin Slightly elevated at baseline in both groups. After the 14 week intervention the level decreased significantly (>20%, p=0.019) in the probiotic group, bringing the concentration into a healthier, normal physiological range.
α 1-antitrypsin No significant differences in either group with treatment or with exercise. Fecal concentrations were normal at baseline and after the 14 week intervention in both groups.
Carbonyl groups on proteins (CP) No differences between groups at baseline, but both groups had concentrations that were 15-25% above normal. After the first exercise intervention CP significantly increased in both groups. After the intervention a post-exercise increase was still observed, but it wasn’t significant.
Malondialdehyde (MDA) Measured MDA values were within normal range and there were no differences between groups at any point either with exercise or with treatment.
Total oxidation status (TOS) Measured TOS values were above normal at all time points but there were no differences between groups as a result of exercise or intervention.
Tumor necrosis factor alpha (TNF-α) Concentrations at all time points were higher than normal. After probiotic supplementation they decreased slightly but not enough to be significant. Exercise had no effect.
Interleukin 6 (IL-6) IL-6 levels were within normal range pre-exercise in both groups at baseline and at 14 weeks. However, in both groups IL-6 increased significantly by similar amounts after exercise at baseline and at 14 weeks.


Intense exercise seems to take its toll on the immune system by compromising the integrity of the intestinal barrier leading to “leaks” and increased permeability. Any type of leak, whether under your sink or in your intestines, is not good.

In the case of your intestines, leaks mean that toxins and other undesirables make their way into your bloodstream. When the bad bugs overtake the good ones, illness usually results.

In this study, after 14 weeks of supplementation with probiotics, zonulin concentrations – a modulator of intestinal barrier function – decreased from slightly above normal to normal range.

This means the probiotics worked to “seal the leaks” by affecting the expression of the signaling pathway that increases intestinal resistance.

Supplementation also decreased protein oxidation and the chronic inflammatory marker TNF-α.

Lastly, the exercise protocol did not induce oxidative stress but increased concentrations of the inflammatory cytokine IL-6.

This means that probiotics don’t have an effect on the normal increase in this signaling molecule as a result of strenuous exercise. That’s neither good nor bad. It merely provides information about how the probiotics worked.

For anyone who exercises intensely, the results of this study seem to point to a role (albeit modest) for probiotics as part of a daily routine. More research needs to be completed with a larger sample size. Including women as well as men, using different exercise protocols and evaluating more strains of probiotics – namely the common ones that you and I buy – would be extremely helpful.

Bottom line

Evidence supports including fermented foods or probiotic supplements into your routine for maintaining a healthy digestive balance. If you decide to try a supplement, choose one that contains a variety of strains and at least 1 billion or more active cells.

If you prefer to stick to foods, fermented foods like sauerkraut, kimchi, sourdough bread, and soft cheese like Gouda are all good sources of various strains of lactobacillus bacteria. Fermented soy foods like miso and tempeh also include over 160 different bacteria strains (5).

So, next time you sit down to a meal, don’t forget to feed your ecosystem!

Eat fermented foods, such as sauerkraut, for a healthy digestive balance.
Eat fermented foods, such as sauerkraut, for a healthy digestive balance.

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