The importance of 'gut health' for athletes.

Alan Couzens, MS (Sports Science)

Feb 10th, 2016

After listening to another great Endurance Planet podcast on ‘gut health’, I wanted to jot down a few thoughts that sprung to mind that may be of some use to serious athletes who may be struggling with ‘gut health’ issues or, on a strongly related note, slow recovery/ general health issues.

A lot of the focus on athletic nutrition has centered around the ratio of the Carbohydrate/Protein/Fat macronutrient breakdown & its impact on performance and health. I've offered my thoughts on the 'right' answer for various athletes/activity levels here. However, there is another important nutrient that is often put in the (literal) 'too hard basket' for hard training athletes - fiber.

This is a mistake. Fiber is one of the most important contributors to overall athletic health on a number of levels. Not only does it 'keep us regular'. It provides a critical barrier to pathogens in our gut & provides an important fuel source for some of our most important (& friendly) 'neighbors'. Let me explain...


First a quick intro to one of the major problems in 'gut health': Dysbiosis (an imbalance of bacteria in our gut)...

The bacteria in our guts has 100 times the number of genes present in the rest of our body. Put another way, about 90% of our organism is bacteria. In a very real way, we’re more ‘bug’ than human. Unsurprisingly, an ‘eco-system’ of this magnitude has a huge bearing on the overall health of its host, i.e. us!

Just how much of a bearing does our gut have on our overall health?

A 2003 animal study by Montagne et al., found a direct link between imbalance(/lack of diversity) in gut bacteria & inferior growth rates, propensity to infection and even premature death(!) among a variety of species.

Yes, like all eco-systems, balance & diversity is immensely important. A healthy person/system has a balance of ‘good’ and ‘bad’ bacteria in their gut at any one time. When things get 'out of whack' & the system detects an imbalance in the bad-v-good ratio, it perceives a threat and reacts in the only way it knows how – our immune system goes on high alert!

When a threat to the overall system is detected, our body starts devoting (energy) resources to the perceived threat. It increases blood flow/inflammation, the output of inflammatory, cytokine producing immune T-Cells increases and, for the moment, it puts less important tasks (e.g. repairing the muscles after a hard training session) on the back-burner.

It goes without saying that for athletes, then, making an effort to maintain this balance of good and bad bacteria in our gut to avoid this 'full alert' auto-immune response & to keep the focus on rest & repair of training related damage is a high priority in terms of maximizing recovery between sessions & preserving overall health.

So how do we do that?

Number 1 – we keep the bad bacteria in its cage!

The real ‘high alert’ phase comes when the body detects these bad bacteria in our blood stream. This occurs when intestinal permeability increases beyond normal levels (i.e. our gut becomes ‘leaky’). This is tightly linked with activation of the sympathetic nervous system - it happens in response to stress (training or otherwise). Perceived stressors force the body to let down its (gut) guard and divert blood and other resources away from the gut to other areas of ‘need’.

In addition to the stress interplay, the body also keeps the bad bacteria out of our blood stream via a protective barrier - a 'mucosy' lining that is created as soluble/fermentable fiber passes through our intestines.

Fermenatable/soluble fiber plays a large protective role in the overall health of the body. A 2003 study by Correa-Matas et al. showed an increase in diversity of the microbiome and a significant protective effect of fermentable fibers against infection in the gut. Additionally, they found that those who did get infected on the high fiber diet had significantly reduced recovery time. The proposed mechanism for this was significantly greater glutamine transport in the high fiber group - a crucial amino acid to both immune function and protein synthesis, i.e. recovery & growth!

This protective role that fiber plays in our immune system brings us to point 2..

Number 2 – we keep the bad bacteria in check by feeding and nourishing an equal number of good bacteria.

Closer to home, a 2011 study on Australian distance runners found a direct correlation between the quantity of the 'good' gut bacteria - Lactobacillus fermentum, & a decreased incidence and severity of upper respiratory tract infections over a season

This ‘good’ bacteria in our gut feeds on short chain fatty acids (which, incidentally, also offer very positive benefit to our blood glucose and cholesterol profiles) that are created when fiber has the time to ferment in our intestines. Hence these fibers are 'pre-biotics' in the sense that they must be present first in order to feed the good bacteria when it arrives - build it and they will come!

Therefore, a large part of keeping our microbiome 'eco-system' balanced comes down to 2 things….

  1. Give your gut the time and blood flow that it needs to properly break down the fiber to feed our friends.
  2. Eat a good amount of fermentable fiber!

While seemingly simple enough, the above can represent a real challenge for serious athletes in training. Let me explain…

One of the highest sources of fermentable fibers is raw onion. Have you ever tried to eat large amounts of raw onion on a training camp? If so, I hope it wasn’t a twin share set up! :-)

Yes, eating good amounts of fiber can be rough on the gut. It can also make you feel quite full – a good thing for weight loss but a bad thing when you’re prioritizing getting a lot of calories in to keep up with high workloads.

During times of big training, it can become an either/or proposition of getting enough calories in to meet energy demands or getting high quality nutrients in to maintain overall health. I should point out, that from a health standpoint, option B isn't any better than option A. Our health can be severely compromised when we run at large energy deficits for extended periods.

So, what’s the solution?

In the podcast, Dr. Tommy hit the nail on the head when he talked about the importance of ‘periodizing’ your nutrition – recognizing the importance of quantity, i.e. just getting enough calories in at various points in the year/month/week when energy demands are high (a training camp etc) but then swinging to a quality emphasis when energy demands are a little more moderate.

During these times when we scale back on training (& life) stress to support our health, fermentable fibers should play a large role. A happy side effect of prioritizing fiber in your diet during these periods is that it is also very satiating – it will make you feel full and you’ll have less desire to eat large amounts of calories so it will keep your bodyweight in check.

Good sources of fermentable fiber…

Basically all of the stuff that your training camp partners don't want to see you munching on :-)

  • Garlic
  • Onions
  • Leeks
  • Brussel Sprouts
  • Carrots
  • Chicory root
  • Legumes
  • Unripe bananas

The above is the stuff you should be including in high quantity (up to 40g/of fiber per day) during your recovery days/weeks/months, coupled with some proactive strategies to switch on the parasympathetic 'rest and digest' system - lots of good quality sleep, SMR, yoga, meditation etc.

This quality/quantity balance is the often unconsidered area of nutritional periodization but it is an important one. In order to maintain nutritional quality, include regular times in your training year (recovery days/weeks/blocks) where digestive stress is low. Facilitate parasympathetic activation at these times to slow down the system and give the gut everything it needs to switch on the 'rest & digest' system, have the time to pull out all of the 'good stuff' from the food passing through & feed the most important exhibits in your 'zoo’.

Not only will this prevent chronic systemic inflammation which can lead to serious threats on your health(!) But, for you as an athlete, it will ensure that when you do stress the system with training, it has sufficient resources to deal with it quickly and efficiently.

Train (and eat) smart,



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