Sunday, May 15, 2022

Need To Poop Mid Race?

Our Singapore cycling champion Donaben Goh came to see me yesterday for one last tune up before he leaves for the Vietnam SEA Games tomorrow morning. We were discussing his fuelling needs in the cycling road race event (167 km long) and talking about stomach upsets while racing.

Familiar sight at races
If you're an endurance athlete, you would definitely have experienced gastrointestinal (or stomach) issues (GI). That includes nausea, bloating, abdominal pain, reflux, flatulence and diarrhoea during your longer traning sessions or races.

How and why does this happen? 

It all starts at the lining of our gut (or alimentary canal from the stomach to the anus, consisting of the small and large intestine), which has 2 jobs. First, it allows food to pass from the gut to our bloodstream and it also prevents nasty bacteria and toxins from entering the same route.

When we exercise, blood from our digestive organs (up to a quarter of our blood) are diverted to our muscles to supply more oxygen to them. Moderate exercise can reduce the blood supply to the gut by up to 70 percent. 

During prolonged endurance exercise (usually longer than 2 hours at 60 percent VO2 max or more), the gut lining starts to malfunction since it is now lacking oxygen and energy. Food that the gut is trying to absorb gets blocked while toxins start to leak into our bloodstream.

In addition, the bouncing and jostling from exercise can cause direct mechanical damage to the lining of the gut. This is why GI issues happen more with running compared to cycling.

Heat and dehydration will divert more blood away from the gut, allowing more gases and/ or toxins to pass through. 

What's worse with GI distress is, it often gets worse when you're anxious or stressed, for example before your big race. Anxiety and psychological stress trigger adrenaline which further diverts blood away from the digestive system while increasing leakage in the gut lining.

How do we prevent it? In a perfect world the obvious approach would be to find out the food that triggers our GI distress and avoid them prior to our races and long training sessions.

Studies show that a class of poorly digested carbohydrates known as FODMAPs (fermentable oliosaccharide, disaccharide, monosaccharides and polyols) may cause GI distress for many of us as they are not well absorbed in the small intestine. This causes fermentation and produce gas in the colon.

This include food containing wheat, milk, onions, garlic, legumes (beans, peas and lentils) and stone fruit (apricots, peaches, plums, mangoes, lychees etc).

Timing matters too, as eating too much fat, protein or fiber 90 minutes before exercise may increase the risk of GI problems. 

Please note that people who keep to low FODMAP diets tend to have less healthy and diverse gut microbiomes.

Personally I've found that 'training your gut' works well. Many other athletes I've spoken to and treated say that eating and drinking energy gels/ bars and sports drinks that are palatable over time makes them less susceptible to GI issues. 

You have to try them out during your long training sessions or less important races. A gel or bar may taste fine at room temperature, but may taste terrible and be difficult to swollow in hot, humid conditions. Research suggests that 2 weks of training the gut can make a difference (Miall et al, 2018).

All the best to Donaben and the rest of Team Singapore at the Hanoi SEA Games.


Miall A, Khoo A, Rauch C et al (2018). Two Weeks Of Repetitive Gut Challenge Reduce Exercise-associated Gastrointestinal Symptoms And Malabsorption. Scand J Med Sci Sports. 28: 630-640. DOI: 10.1111/sms.12912 

Smith KA, Pugh JN, Duca FA et al (2021). Gastrointestinal Pathophysiology During Endurance Exercise: Endocrine, Microbiome And Nutritional Influences. Eur J Appl Physiol. 122(10): 2657-2674. DOI: 10.1007/s00421-021-04737-x

*I did not write about probiotics (supplements) as they are capable of producing a good environment in the gut but do not eliminate symptoms entirely. That's my personal experience as well. Plus 3 out 5 of this review's authors receive research funding from companies that make supplements.

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