Ask an Expert: The Role Of The Gut In Performance Athletes


How addressing physical complaints related to the gut might unlock a competitive advantage for performance athletes

As an avid competitive cyclist in his youth, Floris Wardenaar, Assistant Professor in Nutrition at the College of Health Solutions at Arizona State University (USA), discovered the pivotal role that nutrition played in enhancing his athletic performance. Now, his research and expertise are devoted to optimizing the work of (sports) health professionals and delving into various aspects of performance nutrition. Wardenaar shares valuable insights into common physical complaints experienced by well-trained athletes, and the potential benefits of nutrition in alleviating these issues.

Q: Could you share a little more about your work, and what initially sparked your interest in the field of performance nutrition?

A: My work aims to inform (sports) health professionals on how they can optimize their work, and my research focuses on multiple areas, including but not limited to dietary supplement behaviour, the impact of sports nutrition interventions, hydration, thermoregulation, and gastrointestinal (GI) complaints.

As a young competitive cyclist, I wanted to gain a performance advantage compared to my peers. For me, that was about focusing on my nutrition – before, during, and after each race or training session.

Q: When considering well-trained athletes, what are some commonly observed physical complaints they may experience?

A: Many athletes (four out of five) experience some form of moderate GI complaints, such as belching, nausea, bloating, and flatulence, and one out of five experience more severe GI complaints. Other physical complaints that often occur are muscle cramps, and if people drink more than necessary, they may feel the urge to urinate more frequently, which during exercise can understandably be a nuisance.

Q: Do we know why this might occur? As athletes usually adhere to demanding schedules, could stress also be a factor?

A: The numbers provided above relate to GI complaints during endurance exercise – there isn’t a lot of data on other types of sports. We have seen that some team athletes can report relatively high numbers of GI complaints[i] (in this case, we investigated American Football athletes reporting general complaints, separated from their practice). This is slightly lower than what is observed in endurance athletes – but still very substantial.

Stress could certainly be a factor at play. Some research links anxiety to GI distress – especially for people that compete regularly – and this may have an impact on the type and number of complaints that may be experienced.

Q: It has been widely acknowledged that the role of the gut is important for overall good health. Could you elaborate on the mechanisms of action that are relevant to athletes?

A: GI issues in athletes can broadly be linked to compromised gut barrier function, local inflammation, microbiota disbalance, and exercise stress-related nutrient malabsorption[ii]. A healthy gut should protect against all these imbalances. It’s often believed that GI complaints directly relate to gut injury and/or food intake, yet studies showing a strong relationship in real-life events are scarce.

An idea that has been proposed is that good gut microbiota can help you to keep good gut integrity, reduce inflammation and microbiota disbalance, and therefore also exercise-induced nutrient malabsorption.

Q: On the topic of microbiota – how can nutrition play a role in alleviating these issues? Could it also improve exercise performance?

A: We know that nutrition can cause GI complaints and alleviate GI symptoms. Therefore it’s a sensible idea that when people do not experience complaints that they will perform better, but at the same time it is very difficult to prove that. For example, improved gut health leads to improvements in exercise performance. We have seen in a recent study[iii] that athletes that score reduced GI complaints, also tend to self-report better general well-being and a better trend toward mental well-being and sleep.

Q: It appears that addressing physical complaints among elite athletes could provide a competitive advantage, as it may also help to address underlying mental challenges associated with their demanding careers. Considering the rising activity levels in the general population, could there be similar benefits for them as well?

A: From experience, I know that certain physical complaints can make an athlete insecure. By removing the complaints, well-being can increase, and therefore it potentially may result in better performance. On the other hand, especially when we talk about GI complaints, athletes experience all types of complaints during their exercise activity – and in some way, these complaints are part of their performance.

The strange thing is that when you ask ultra-endurance runners about their complaints while they are running, you do not get a lot of issues reported – even though as an observer you hear them huff and puff while showing multiple signs of GI complaints. It’s not until afterward that they will report these actual complaints. So there seems also a disconnect during exercise between actual complaints and how the athlete experiences them while being active.

Q: Strange, but interesting! Are there any theories as to why this might occur?

A: I don’t know of any theories circulating in the literature about this. It’s something that I have personally noticed during an observational study performed in an ultramarathon covering 120 km.

My best bet? The brain filters out or blocks certain stimuli while performing arduous exercises, but the systems behind this go beyond my expertise.

Q: Many people are leading an increasingly active lifestyle. Although your work focuses on athletes, could these insights also be relevant for the everyday athlete?

A: Yes, for sure! Being active will influence your fitness level, and this likely will impact elements that influence overall well-being, such as gut health. At the same time, all type of exercise that goes beyond your initial comfort zone may impact how you feel.

Although it’s reasonable to believe that gut injury leads to GI complaints, we mostly see moderate correlations between both – similar to the fact that we see a moderate relationship between GI complaints and the intake of certain foods or nutrients. The causes of the complaints are likely complex and multifactorial. Therefore, there is unlikely a one size fits all approach, and the approach to relieving these complaints should be looked at on a case-by-case basis.

About Floris Wardenaar

Floris Wardenaar was born in Amsterdam, the Netherlands. Despite the fact there was no previous history of competitive sports within the family, all the brothers were competitive in different areas of sport. At the age of 14, he started cycling, both on the road and the track. From that moment on his interest in performance nutrition grew. During his second year as a junior cyclist, he was selected for the newly formed National track cycling team. As part of his cycling career, he collected more than 30 stage places and victories.

Wardenaar studied nutrition and dietetics at the Hogeschool van Amsterdam (HvA, Amsterdam Applied University) with specific interest in sports nutrition. Following this, Wardenaar started a master’s program at Wageningen University in human nutrition and physiology. During the second year at Wageningen, he founded his own consultancy firm in sports nutrition advice and during the third year he was full-time vice-president of the Dutch Chamber of Student Associations (LKvV). Subsequently he followed an internship at the Department of Kinesiology at the University of Texas in Austin and wrote his master’s thesis on the interaction between alcohol consumption, exercise and blood glucose levels at SENECA, expert centre of HAN Sports and Exercise Studies at the HAN University of Applied Sciences at Nijmegen. He graduated in 2005 both in nutritional physiology and in nutrigenomics.

In September 2012 he commenced his doctoral project in cooperation with Wageningen University, which was partly financed by a regional grant Eat2Move. At the beginning of 2013 he became program manager of work package 3 within Eat2Move and from 2014-2017 he was team leader of the Team Nutrition of the Dutch Olympic Committee.


[i] Wardenaar et al. Unpublished, currently under review.

[ii] Costa, RJS, Snipe, RMJ, Kitic, CM, and Gibson, PR. Systematic review: exercise-induced gastrointestinal syn-drome—implications for health and intestinal disease. Aliment Pharmacol Ther 46: 246–265, 2017.

[iii] Wardenaar et al. Unpublished, currently in preparation.


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