The forgotten factor for optimal gut health

For the vast majority of people looking to improve their gut health, the entire focus is on diet and probiotics.  Diet is a powerful factor in regulating the gut and microbiome, but it’s just a single factor.  Other important factors include meal timing, stress, sleep/sleep timing, and physical activity.  In this blog we’ll focus on physical activity.

We can break physical activity up in to 2 separate subgroups: Low level physical activity and moderate to vigorous physical activity.  Both are important for regulating the microbiome because both will change your internal workings.  This includes:

  • Maintaining an ideal blood glucose range
  • Regulating insulin secretion
  • Modulating the inflammatory response
  • Increasing bile flow
  • Modifying bile content
  • Regulating stress hormone secretion (adrenaline, cortisol, etc.)
  • And more…

There’s no greater misunderstanding with regard to the microbiome than the fact that it’s multifactorial.  Focusing solely on diet is probably the biggest obstacle preventing people from changing their microbiome and healing their gut.  In this blog I’ll cover how moderate to vigorous physical activity can change the microbiome and heal the gut.

Before we dig in to this, let me state something important.  There’s absolutely no way you are going to optimize your microbiome or gut health without regularly performing moderate to vigorous cardiovascular exercise.  Period.  Now let’s find out why…

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Cardiovascular exercise, the microbiome, and the data

There’s loads of data showing exercise to be a powerful regulator of the microbiome.  There are too many animal studies to count showing positive changes in the microbiome with exercise.

There are studies showing exercise to improve microbial diversity and immune function(1)

There are studies showing that exercise blocks the negative effects of exposure to environmental toxins(2).

And there are even studies showing that changes due to exercise are independent of changes made via diet(3).  This is pretty important because that means changing both can have an additive effect.

But maybe animal studies aren’t your thing.  There are a few studies in humans we can look at as well.

There’s a study in rugby players showing increased microbial diversity compared to non-athletes(4).

There’s a study showing cardiorespiratory fitness is correlated to microbial diversity, particularly to butyrate producing bacteria(5).

Yet another study shows better cardiorespiratory fitness to be indicative of increased microbial diversity in breast cancer survivors(6).

There’s a large body of evidence showing that exercise may be a powerful modulator of the microbiome.  I use “may” because I don’t want to overstate the science.  If you’re looking for some huge randomized clinical trials on this stuff you aren’t going to find them because they don’t exist.

What we do have is a bunch of preliminary data coupled with some pretty powerful mechanisms that can shape the microbiome and gut health.  Let’s take a look at these mechanisms.

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Bile and cardiovascular exercise

One of the more striking benefits of cardiovascular exercise is a change in bile composition and output.  Cardiovascular exercise has been shown to increase bile flow and the bile acid content of bile in mice(7, 8).

Another study found that mice that were fed a diet that caused gallstone formation were protected against gallstones when they exercised.  Mice that didn’t perform exercise had gallstones that were 2.5x larger than mice that performed exercise(9).

Both are likely due to an increased bile acid content in mice that exercise.  Bile with a higher percentage of bile acids is less likely to form stones and is better at emulsifying fats.  Basically, exercise caused the conversion of cholesterol to bile acids which lowered cholesterol saturation of bile.  Greater cholesterol saturation promotes gallstone formation.

There’s quite a bit of talk about “sludgy bile” as a problem for people.  The way I see this discussed is that it’s a consequence of accumulated toxins in the bile.  A more likely scenario is that the bile is “sludgy” because it isn’t flowing properly.

Like the oil in a car, proper flow is required to prevent sludge.  This could help explain the results of the study where mice were protected against environmental toxins with exercise(2).

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Bilirubin and exercise

Cardiovascular exercises changes bile in another important way.  Red blood cells are responsible for carrying oxygen to tissues for use in aerobic energy generation.  As red blood cells become old and damaged, they rupture and release their contents in to the plasma.  This process is called hemolysis.

Heme is the protein in red blood cells responsible for carrying oxygen.  During hemolysis, the enzyme heme oxygenase 1 breaks heme in to iron, carbon monoxide, and biliverdin.  Almost instantaneously, biliverdin is converted in to bilirubin.

One of the adaptations to chronic cardiovascular exercise is an increase in red blood cell turnover.  The whole process of transporting oxygen is improved.  You make more red blood cells, each of those red blood cells carries more oxygen, and these red blood cells die and are replaced more often(10).  This leads to more bilirubin being created and mildly elevated serum bilirubin levels(11, 12).

I’ve mentioned bilirubin before as it’s a very interesting molecule.  (Check out this blog for more info)  Bilirubin was once thought of as a toxic byproduct of heme breakdown due to its role in jaundice.  The problem is, it makes no sense to convert biliverdin in to bilirubin if bilirubin is toxic.  Biliverdin is water soluble and can be easily excreted in the urine.  Bilirubin is fat soluble so it sticks around.

This has led to a new role for bilirubin as a fat soluble antioxidant.  While an extremely high level of bilirubin in the blood is bad due to its toxic effects, levels in the high reference range appear to be protective.

Studies have shown mildly elevated serum levels of bilirubin to be protective against cardiovascular disease(13).  Another interesting finding is that people with Gilbert’s syndrome, a benign disorder where bilirubin sticks around a little longer, are protected against cardiovascular disease(14).

If bilirubin is indeed protective against lipid oxidation, it would be a very important factor for gut health.  Your intestinal barrier is effectively a force-field of lipid based plasma membranes and bilirubin is sent through the gut several times a day with bile.  Having an antioxidant capable of repairing lipid-based molecules cycle through the gut is extremely helpful in maintaining a healthy gut.

On the microbiome side of things, stool and urine color are both a product of bilirubin being acted on by your gut bacteria.  Pale stool or clear urine can indicate that this process isn’t happening.  This could be due to low bilirubin flow through the gut or a lack of bacteria that carry out this task.  I can tell you from experience that cardiovascular exercise is a powerful tool to improve this situation.

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Cardiovascular exercise and pancreatic enzymes

Now that we’ve covered bile, the next stop on our journey is next door at the pancreas.  During digestion, the pancreas stores and secretes enzymes that break down proteins, fats, and carbohydrates.  This helps digest the food you eat in to absorbable units.

As a chronic adaptation to cardiovascular exercise, the pancreas stores more pancreatic enzymes and ejects them in to the duodenum much faster than in sedentary controls(15, 16, 17).  This improves digestion but also has another benefit.

The pancreas also secretes bicarbonate in to the duodenum when the acidic contents of the stomach empty in to it.  This increases the pH and protects against acid induced injury.  This is important because enzymes have a pH where their activity is maximized.  Most of the enzymes in the duodenum function best at a higher pH.

Cardiovascular exercise: A requirement for optimal digestion?

An important concept here is that the default condition for humans is high levels of physical activity.  What I mean by that is for most of our evolution, survival has been dependent on high levels of physical activity to attain food.  Now…not so much.

When you remove an environmental factor from your lifestyle that was part of the default condition for so long, you change physiology in a profound way.  A great example of this is what happens to astronauts in space.  When you remove gravity, part of the default condition, there are major consequences to health(18).

The longer an environmental factor has been part of the default condition, the more likely removing it will have a substantial impact on physiology.  Our lack of physical activity has certainly had an impact on our waistline and physique.  Given the evidence, it’s not completely out of the realm of possibility that it impacts digestion as well.

Something you may have to come to grips with if you have a digestive disorder and are sedentary is that you have to get up and moving.  I think the major block here is that people often look at things through their own perspective which is completely normal.  But when you are looking at things from a biological view, evolution should be the perspective you take.

From an evolutionary point of view, physical activity doesn’t improve digestion because it’s the default condition.  On the contrary, it’s physical inactivity that reduces digestive efficiency because it’s the more recent environmental condition.

So from this perspective, your digestive disorder isn’t improved by increasing physical activity.  In fact, your digestive disorder is a consequence of your lack of physical activity.

But this sets up a troubling scenario.  In many people, a digestive disorder makes them averse to physical activity because they either have no energy or exertion makes their symptoms worse.  And by limiting physical activity they are making their digestive disorder worse.  In effect, they are reinforcing their digestive disorder by avoiding physical activity.

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Minimum requirements for moderate to vigorous physical activity

The US government recommends a minimum of 150 minutes per week of moderate to vigorous activity for optimal health.  In my opinion, this is just the starting point for gut health.

There are modern pockets of hunter gatherer tribes that give us a glimpse in to the amount of physical activity we evolved under.  While most people in the Western world struggle to get 150 minutes of moderate to physical activity per week, members of a modern hunter gatherer tribe called the Hadza attain it in just 2 days(19).

Moderate physical activity is actually not as difficult to get as you think.  Walking at a good pace for 10 minutes or more qualifies as moderate for most people.  If you do that twice per day every day you’re almost at the recommendations.  Most activity trackers on the market will calculate this number for you.  I use a fitbit and get in the 300 range pretty much every week.

Fitbit active minutes

It may seem that this amount of weekly physical activity is easy to attain, and that’s because it is.  Despite this perception, fewer than 10% of adults in the US meet this criteria(20).

They think they do.  In a study from 2011, participants reported that they got 324.5 minutes of moderate physical activity per week.

When it came to put up or shut up, researchers strapped an activity tracker on them and this painted a different picture.  The trackers showed the average participant got 45.1 minutes of moderate physical activity per week(20).  This doesn’t even take vigorous physical activity in to consideration.

While I also believe that you should get some higher intensity activities during the week, you don’t need a ton.  While moderate physical activity appears to promote good digestion and a healthy microbiome, too much higher intensity activity is actually detrimental.

Another important thing to take in to consideration is your current state.  If you’ve been laying in a bed for 2 months the last thing you should do is get up and go for an hour-long walk.  Start low and work your way up slowly.  Over-stressing your system is the last thing you want to do, as I’m sure many of you with digestive disorders will attest to.

Where does gut healing begin?

Let’s be honest, anyone with any type of problem wants a simple solution and the gut is no different.  In my personal opinion, gut health begins with the default condition.  I consider the default condition to be the one our ancestors thrived in.  This includes:

  • Regular fasting
  • Waking up early and exposing your eyes to the sun early in the morning
  • Getting well above 150 minutes of moderate to vigorous physical activity per week
  • Managing stress
  • Limiting the amount of time you sit every day
  • Eating a healthy amount of food that’s minimally processed
  • Reducing your exposure to artificial light at night
  • Getting to bed at a decent hour and sleeping

People often want to know if they should take methylfolate, digestive enzymes, or try coffee enemas.  They want to know if acupuncture works, if floating improves health, or if using an infrared sauna will help heal X.  The truth is, if you’re looking for the solution to your problem, it start with the 8 bullet-points above.  That other stuff may help, but it’s definitely not where you should start.


If you’re someone who’s looking to improve your digestion and heal your gut, you absolutely need to be physically active.  Moving is the default condition that our ancestors evolved under so our fairly rapid descent in to physical inactivity has caused profound changes in our physiology.  I think there’s enough mechanistic evidence out there to take action.

Current government recommendations state that we should get at least 150 minutes per week of moderate to vigorous physical activity for optimal health.  In my opinion, this is a very low bar that most people never meet.

Looking at the Hadza can give us guidance and paints a very dire picture of our physical inactivity.  Not only do they exceed this amount in 2 days, they get 14x the amount of physical activity that we do(19).  This may partially explain their greater microbial diversity than people living a more modern lifestyle(21).

Moving forward I plan on covering all of the other bullet-pointed stuff.  There are other factors that are important such as establishing strong social connections.  But I think the above list is a great place to start.  Join the private facebook page here and follow all of the action.

Interested in improving your digestion, protecting your digestion while taking pharmaceutical drugs, or deciphering your digestion woes ?  Shoot me an email by clicking the “contact” page on the menu at the top and we can see if I can help. 

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