When I first began writing this blog I decided I wanted to start a private group on Facebook to help direct some of my research efforts.  I wanted to interact with my readers in a way that would allow me to dig in to some of the things that mattered most to them.

If you’ve read most of my work, you know that I think bile flow is a crucial piece of the puzzle in optimizing gut health in general and digestion in particular.  Bile plays many roles in helping set the microbiome by regulating motility, preventing SIBO by causing the secretion of antimicrobial peptides, and promoting an environment that selects for commensal microorganisms over pathogenic ones.

One of the most frequent questions I received early on was what someone without a gallbladder should do to optimize their bile output.  I didn’t have an answer then, but after doing a little digging I believe I may have that answer.

But, the answer I came across isn’t specific to people with poor bile flow or a missing gallbladder.  In fact, what I found may answer the question, “How do you optimize bile output in all organisms?”  Even if it doesn’t answer that question, the study I found that provided the answer was done in humans, so it directly applies to us.

Timing is everything…

After a substantial amount of digging through the interwebz, I came upon a study that looked at bile output in humans.  One of the most powerful concepts you’ll get from circadian research is that timing matters…a lot.

People understand that they need to get physical activity.  However, what if when you do physical activity is just as important of a concept as how much you do?  That’s what lead me along the path to find this excellent study.

Before we dig in to the study, I feel it’s important to go over the limitations of the data and some of the strong points.  First, it was a tiny study, only 11 participants and they were all male.  Second, the study was conducted in 1979 and hasn’t been reproduced since.  Finally, measurements were recorded while people performed their “exercise” while lying in bed and cycling on an ergometer which isn’t exactly real world conditions.

While those are some pretty significant limitations, there is one factor that makes the data very intriguing.  This study was performed using a within-subjects design.  What this basically means is that each person was measured under a no-exercise condition and an exercise condition.

Basically we’re getting a look at Joe’s bile output while being sedentary vs Joe’s bile output while exercising and not what Joe’s bile output while exercising looks like in comparison to Steve’s bile output while being sedentary.  In other words, individual genetic variability isn’t a factor in the data.  And since the measured difference in bile output between the 2 conditions was so large, the authors obtained significant results with such a small number of subjects.

The study…

In the study, participants had a tube placed in their duodenum to measure bile output every 30 minutes.  They were restricted to a bed during both conditions to prevent the tube from becoming dislodged.

Bile output in to the duodenum was then measured over 9 data points during strict bed rest or while exercising with a bicycle ergometer for 1 hour.  As mentioned, each subject had measurements taken during both conditions and the order in which they were exposed to each condition was randomly determined.

When the data was collected and analyzed, the researchers found that physical activity caused a substantial increase in bile acid output in to the duodenum.  Bile acid output was 242 micromol/30 min in the sedentary condition and increased to 2,204 micromol/30 min in the exercise condition.

This is a pretty substantial increase in duodenal bile acids, but where the bile acids came from is even more interesting.  The researchers measured changes in the size of the gallbladder to see if the bile was coming from there.

As it turns out, the gallbladder didn’t decrease in size, it increased.  This indicates that the bile was not coming from gallbladder contraction, it was coming directly from the liver.  It also indicates that physical activity may help the gallbladder fill to an even greater extent than when you are sedentary.

This data indicates that physical activity may increase bile acid output in to the duodenum by a factor of 10 in comparison to being sedentary.

Physical activity and feeding: Should they be coupled?

This data brings up an interesting point:  Does feeding need to be coupled to physical activity in order to optimize digestion?  Every other organism on the planet, from bacteria to mammals, performs physical activity in order to procure food.

Modern humans have managed to decouple physical activity from acquiring food through technological advances that allow for mass food storage and distribution.  Keep in mind this is a relatively new phenomenon.

Even agricultural humans 50 years ago had to do something physically active to acquire food.  Food acquisition, distribution, and storage were limitations that have only recently been lifted from us.  As a result, we’ve decoupled physical activity from food consumption.  Based on this limited set of data, it would seem that this would have a major impact on our digestion and absorption of fats and fat soluble vitamins.  It could also promote a less than ideal gut.

The significance of pre-meal bile output

So what would the dumping of bile acids in to the duodenum with physical activity do for us?  Primarily, it would saturate the mucus layer in the small intestine with bile acids in anticipation of a meal.  This will tighten up the intestinal barrier, restrict the growth of bacteria, promote motility, and improve the digestion and absorption of your meal.

If that meal doesn’t come, the bile acids will simply make their way to the ileum and be recycled for later use.  When that happens, antimicrobial peptides are released in to the mucus layer to prevent bacteria from overgrowing there.  (You can read all about the above wonderfulness in a blog I wrote called Is bile the key that turns the gut clock?.)

Since these bile acids are coming directly from the liver, the gallbladder still has stored bile acids for when the meal comes.  The assumption has always been that gallbladder emptying is the most critical aspect of bile secretion for meals.  But this doesn’t explain how people without a gallbladder can digest and absorb significant amounts of fat without gallbladder bile output.

Perhaps the primary driver of bile in to the duodenum is the coupling of physical activity to food consumption.  This anticipatory saturation of the mucus layer in the small intestine would certainly optimize digestion and strongly influence the gut.  Gallbladder emptying, then, would be more like the cherry on top.

Conclusion

This tiny little study in humans may have some big implications for food digestion and absorption as well as regulating the gut and microbiome.  During 99.99999999% of evolution of life on the planet, physical activity has been coupled to acquiring food.  It’s quite possible that physical activity induces some processes that are necessary for the proper digestion and absorption of nutrients.

Bile acids also play an important role in regulating the environment in the gut and inhibiting the growth of bacteria in the small intestine.  It’s no secret that nearly all of the exposure to bacteria in our gut comes from when we eat.  Physical activity prior to exposing our gut to food-based bacteria may be a crucial factor in ramping up mucosal defense against pathogenic bacteria and in promoting an environment where commensal bacteria can do their job.

Overall, this study indicates the physical activity should precede food consumption for optimal digestion and gut function, both in the short- and long-term.