What do exercise and a diet high in fibre have in common? We’ve known for some time now that both of these are good for our gut health and decrease our risk of colon cancer. However, it seems as though there may something extra that fibre and exercise have in common, and it comes as a fatty acid called butyrate. This link between exercise, fibre and gut health will be explored, and you’ll see that the effects travel as far as the brain.

What actually is butyrate and what does it do?

Butyrate is a short chain fatty acid produced by our gut bacteria as they break down foods that are high in fibre. Resistant starches are a type of fibre, that are some of the best fuels for these butyrate producing bacteria (Bourassa 2016). These starches come in foods such as legumes, oats and starches that are cooked and cooled like potato and rice salads.

Now butyrate is an important fuel for the cells of our colon. In fact it supplies up to 70% of their energy (Bourassa 2016). Keeping your colon cells healthy is thought to be one of the reasons why higher butyrate levels decrease your risk of colon cancer by 50% (Matsumoto et al, 2008).

However, the benefits of butyrate go well beyond reducing our risk of colon cancer. This is because healthier gut membranes improve their integrity (how closely they bond together) allowing them to act as a better barrier, which has flow on effects to improving our immunity and reducing inflammation (Ji Wang et al, 2018).

What’s the evidence on exercise and gut health?

Most of the interest on the effect of exercise on butyrate levels started back in 2008. Matsumoto and colleagues showed that butyrate levels, and the bacteria that produce butyrate, were higher in rats that exercised versus a sedentary control.

In 2014 a group of Irish researchers found that professional rugby players had a greater diversity of gut microbiota than a group of sedentary controls (Clarke et al, 2014). However a signifiant limitation in this study was that professional athletes eat very differently than the general population. And these results could possibly be related to their diet and not their activity.

We had to wait until late last year when a group from the University of Illinois designed a study that looked at the impact of aerobic exercise on butyrate. Previously sedentary individuals were asked to exercise three times a week for a 6 week period (Allen et al 2017). What they found was that there is a link between butyrate, exercise, and gut health in humans.

Much like the rodent study back in 2008 they found that aerobic exercise increases the levels of butyrate along with the colonies of bacteria that produce butyrate. Interestingly this effect was most pronounced in lean subjects. The overweight group did still increase the colonies of the butyrate producing bacteria (not to the extent of the lean group) but they didn’t see an increase in butyrate levels in their stools.

Exercise and gut health can also improve your brain!

Now here is where it really gets interesting. The term “your gut is your second brain” has been well used over the last decade. This has been used to explain that the enteric nervous system of the gut is not only quite complex, but it also  has the capacity to signal the brain via many neurotransmitters.

We know that butyrate can cross the blood brain barrier and it is well known to suppress HDAC (Histone deacetylase; Bourassa 2016). Now HDAC inhibitors will increase the expression of BDNF (Brain-derived neurotrophic factor) in the brain. This is important for memory and learning as BDNF is like fertiliser for the brain. It helps your brain cells grow in number and connections!

So where’s the research at?

An interesting experiment, albeit in mice, was published back in 2013 where mice were given an object recognition memory task that is usually not enough to form in either their short or long term memory (Intlekofer et al, 2013). They had a sedentary group and a group that was exercising 3 weeks before the task. They also had a sedentary and exercising group that was injected with butyrate.

The non-butyrate injected sedentary mice could not successfully remember the task 24 hours post initial exposure However, both the sedentary/butyrate injected group and the exercise group could. And when it came to remembering the task 7 days after the initial exposure, it was only the butyrate group that could.

It is important to know that the exercise group only did so for the 3 weeks leading up to the task, and not during the 7 days after the task. This highlights that to get the improved learning outcome, continual exercise exposure is needed.

This mechanism of increased BDNF release via butyrate is probably why we see that children who are fed a high fibre diet perform better in cognitive tasks than those on a low fibre diet (Bourassa 2016). And it could also be the reason why it shows promise in the treatment of neurodegenerative diseases (Bourassa 2016).

We also know that aerobic exercise has an effect on increasing BDNF levels, and this may be why individuals have a 20% improvement in learning tasks (Winter et al, 2007). So it makes sense to eat a high fibre diet and exercise at the same time right?  

 

Take home points about exercise and gut health:

  • It appears as though aerobic exercise continues to benefit our health in many different ways, and improving our gut health is another reason to be active. Aerobic exercise of around 30 to 60 minutes a few times a week can give you this benefit to your gut.
  • Improve the diversity of your microbiota through eating foods that are high in butyrate producing fibre such as legumes, oats and potato salads.
  • Combine this with regular exercise to improve the butyrate production of your gut as this have effects that travel to your brain.
  • And while there is still much more research to be done, it seems to indicate that by doing this you are improving your capacity to learn and remember things, along with decreasing your risk of developing neurodegenerative conditions such as Alzheimer’s.

 

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