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Unraveling Runner’s Guts

Runner's Guts

Unraveling Runner’s Guts
By Alan McCubbin
Image © nito / Dollar Photo Club

Runner’s guts; a potentially embarrassing and completely disarming problem most runners will face at some point. Have you? Well, if you’ve ever been trotting along and felt the unforeseen and dramatically urgent need to find a toilet, you can probably claim an attack of runner’s guts. A while back the issue was raised on Facebook by Rachel M and I figured it was the perfect topic for bugging a highly respected sports dietician, Alan McCubbin.

Alan is the President of Sports Dietitians Australia, an Accredited Practicing Dietitian and an SDA Advanced Sports Dietitian with ten years of experience in the industry. He is also the founder of Next Level Nutrition where he provides expert advice and support for athletes of all levels. Read what Alan has to say about the ‘trail trots’:

This sounds like a very simple question to answer, but in fact it’s incredibly difficult. Our gastrointestinal tract is a complex beast, and there’s lots of different reasons that runners can experience problems, many of which we don’t really understand or have good answers for yet. The main reason for this is that gut issues in runners are difficult to study, because they’re often unpredictable in their nature. So a lot of the research done to date is what we call observational – where runners have been observed in events to see what happens, and trying to pick out any underlying themes as to why the problems might be occurring.

But to start off with we need to understand what we’re talking about when we say “runners gut”. Runners can experience all sorts of gastrointestinal problems during exercise. Starting with the top half of our gastrointestinal tract, we can experience nausea, reflux or vomiting during exercise. The causes of these are many and can range from similar issues that can occur at rest (but exacerbated during running either due to the intensity, the movement of our organs as we run, or the consumption of food and fluid during a run) or something that’s more specific to exercise. Then there are lower gastrointestinal issues, ranging from abdominal pain, bloating and gas, through to needing to visit the toilet! When most people think of “runner’s gut” though they’re referring to bowel issues, and needing to get to a toilet – fast. So that’s what I’ll focus on here.

There are a few things that have been observed to be at least in some way associated with runner’s gut. Firstly, we know that some people never have any problems, regardless of what they do before and during exercise. Others have tried everything under the sun and still have problems. Whether this is genetic or due to some other factor is not really understood.

We also know that runner’s gut is more common at higher intensities of exercise, in younger people and in more elite runners. This is probably at least in part because at higher exercise intensities more blood is flowing to working muscles (and to the skin to dissipate the body heat produced by the working muscles). As a result, less blood flows to the gut.

As far as diet is concerned, there are a few issues that can potentially cause gut issues:

Malabsorption of carbohydrates and related food components – known as FODMAPs. FODMAPS can cause abdominal discomfort, bloating, gas, diarrohoea and constipation. People who experience these issues at rest will also experience them during exercise. But in addition, recent research at Monash University suggests that some people that have no issues normally will actually experience problems with FODMAPs during exercise, probably because the amount of FODMAPs consumed during a run can be increased compared to normal. The major FODMAP component that exist in sports food and drinks is the fructose component, which is present in the majority of commercial products.

Fructose can actually be beneficial to performance in some scenarios, which is why it’s added, but for some people it causes them no end of problem.Going for fructose-free products can assist with this. Of the commercial energy gels commonly available in Australia, I only know of three that are fructose free – Hammer, Shotz and Winners. As far as sports drinks are concerned, the only one I know of that’s completely fructose free is Hammer HEED. But remember that these products are constantly changing and new ones emerging, so this could be incorrect from next week!

Also bear in mind that some people may benefit from eliminating (or at least reducing) FODMAPs in their day-to-day diet in the hours leading up to a run as well.In addition, most people will only absorb a limited amount of carbohydrate during exercise, even the non-FODMAP components. Generally speaking, the average person only absorbs around 60 grams per hour of glucose (the main sugar that carbohydrates are digested down into), as well as 30-40 grams per hour of fructose (assuming no FODMAP issues as discussed above). But researchers in this area will tell you that the individual variation is very large – some people won’t absorb more than 20 grams an hour, while others can shovel in 100g or more in an hour and absorb the lot.

The good news is that the gut can adapt and become better at absorbing carbohydrate, but like all forms of training it takes practice. Consuming race-like quantities in training regularly (at least once a week) will probably assist. The Monash Uni team found that runners could improve their absorption of carbohydrate in as little as ten training sessions, provided they were pushing their gut by consuming more than they could already tolerate.

Caffeine and high doses of Vitamin C, Zinc and Magnesium –  These nutrients are considered a gut irritant to some people in large doses. So for some people it’s simply a matter of cutting out caffeine in the hours leading up to a run, as well as during it. For others however it doesn’t seem to make any difference whatsoever. Likewise, if you’re taking Magnesium, Zinc or Vitamin C tablets, or even a multivitamin with large doses of these, it might be worth going without them for a couple of weeks to see what happens.

Protein, fat and fibre – Observational research suggests that runners who consume foods and fluids that are high in protein, fat and fibre during exercise are more likely to have gut issues when they run compared to those who don’t. Based on this, many experts suggest deliberately reducing the amount of protein, fat and fibre in the 3-4 hours leading up to a run, as well as during it. But I’ve yet to see studies where one group tried this approach and the other didn’t, to really show whether or not it makes a difference.

Hydration – It’s unclear exactly why (possibly the blood flow issue discussed above) but reduced hydration may also be a cause of runner’s gut. On the flipside though overhydration can cause gut issues as well. Dehydration is more common in elite athletes who produce more body heat, and hence sweat losses, and in moderate distance events (20-40km) where the intensity is higher than ultras and there are relatively less opportunities to drink. Marathon distances and above in recreational runners and ultra distances in recreational and elite athletes are more likely to result in over-hydration because the body heat production (hence sweat rate) is lower, there are more opportunities to drink and it’s easier to stomach drinking more at the lower intensity.

If you’re drinking when you’re not thirsty, especially in longer distance events, then there’s a good chance you could end up over-hydrated. The only way to really know is to get a rough estimate of sweat losses during exercise by weighing yourself before and after. The weight loss (after accounting for food consumed that adds weight and toilet stops that reduce weight) is a reasonable estimate of fluid losses from sweat, where 1 gram of body weight lost is equivalent to 1mL of sweat. Bear in mind though that you need to replicate the environment (temperature, humidity) and pace you’d be racing at in order to accurately estimate race fluid losses.

As you can see, runner’s gut is not a single problem with a single solution, it’s a symptom that can occur as a result of one or more potential problems. And because we don’t fully understand all of these problems from a scientific perspective, it’s impossible to give a one-size-fits-all solution. What I would suggest is to experiment in training with some of the factors above. Only ever change one thing at a time so you can tell what’s working and what’s not. And never, EVER try something for the first time in a race. Finally, if you’re still not getting anywhere then I’d suggest you consult with an Accredited Sports Dietitian who has experience in this area – they can look at all the individual factors that might be affecting you, and help you put together a specific eating plan to try and pinpoint the cause and potential solutions to your problem.

To say thanks to Alan McCubbin for sharing his knowledge and time, be sure to click over and check out his web home at Next Level Nutrition. Click here to head on over that way. You can also follow Alan on Facebook. Click here to head to the Next Level Nutrition Facebook page.

Will Lind
About Will Lind (168 Articles)
A minimalist runner that otherwise doesn't discriminate, Will Lind is the Editor-in-Chief and Founder of Functional Running. A true run lover, Will's passion encompasses the full spectrum of running and lies in the soul of the run. A Personal Trainer, Run Coach and romantic at heart, Will enjoys flipping from heartfelt run reflection to critical analysis on a whim.
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