Plant-based runner with digestive challenges a case study


Gastrointestinal distress is a common issue, especially among long-distance runners. Simone do Carmo shares an interesting case of a competitive plant-based runner that shows how improving gut health can have a major impact on an athlete’s performance.

John was a 19 year old, competitive long-distance runner and full-time student with a typical A-type personality: ambitious, determined and competitive. He ran 80 to 120 km per week, including long runs and high-intensity track sessions. He also incorporated core sessions, some light cycling for active recovery and a complete rest day. John approached me in May 2018 because of gastrointestinal issues compromising his performance.

During our first consultation, we looked at his timeline, a tool used in Functional Medicine, that looks chronologically into a client’s case history. John had developed IBS-like symptoms in September 2017, particularly loose bowels and bloating. These were more prevalent during his training sessions, which often had to be cut short to go to the toilet.

Gastrointestinal distress complaints are very common among endurance athletes (1). Considering his training and timing of his symptoms, his running was likely a major trigger. The bouncing effect and reduced blood flow to the gut during exercise were probably compromising his gut function (1,2). Heat stress was not overly a concern as he trained in cold-to-mild conditions.

Both of his grandfathers had suffered from bowel cancer and his sister had been diagnosed with IBS and iron deficiency anaemia. There therefore seemed to be a genetic predisposition towards gastrointestinal problems and malabsorption. John also had a history of taking antibiotics: first in childhood for a toenail infection and again in November 2017, when he took a strong course of antibiotics for a blood infection, which he described as very scary. The antibiotics could also have been both a predisposing factor and a mediator of his gut problems, since research shows that gut microbiota are disturbed during antibiotic treatment and can take several months to recover (3,4).

In June 2017, John turned vegan for animal welfare reasons. He felt good on the diet despite his symptoms and did not want to change. This was a lightbulb moment for me as the change in his diet was close to the time he developed symptoms – was this a major trigger? John additionally started university in September 2017, which could also have been a triggering event. In December 2017, he desperately asked his aunt, a doctor in Australia, for advice. She recommended a low-FODMAP diet that has been shown to improve IBS symptoms (5). Since then, he self-managed with this diet and avoided gluten. Although he noticed minor initial improvements in his symptoms, he felt that the low-FODMAP approach was not working. Since a low-FODMAP diet should only be followed for six weeks (6) and one of his main symptoms was loose stools, micronutrient deficiency and malabsorption were a major concern.

After analysing John’s diet, I determined that his overall nutrition intake was good for a vegan following a low-FODMAP and mostly gluten-free approach, although it lacked some variety as he often ate the same meals every day. But he met his energy demands and was conscious of his food choices. He took no supplements because he disliked the idea.

In terms of macronutrients, John’s intake was 7.5 g/kg of carbohydrates, 1.3 g/kg of protein and 1.6 g/kg of fat, which is in line with sport nutrition guidelines. However, his protein intake could have been slightly higher due to the lower digestibility of plant proteins compared to animal proteins (7,8). The only major concerns in his micronutrient intake were iodine, vitamin D and omega-3. 

First interventions

Based on John’s goal of improving his IBS-like symptoms, the focus of my intervention was to restore his gut health through a food-first approach, supported with supplementation, training modifications and stress management strategies.

Testing and diet

I firstly advised John to have basic blood tests done to check his iron and vitamin B12 status since he was worried that he might be anaemic, and vegans often have subnormal vitamin B12 levels (8,9). This aimed to reassure him because he had an analytical personality and wanted to see data before taking any tablets or supplements. Meanwhile, I encouraged him to ensure that his plant-based milk was fortified with vitamin B12 and to incorporate nutritional yeast into his diet, a good vitamin B12 vegan source (8). Further testing was not possible due to budget constraints.

I encouraged John to introduce more variety into his diet and to slowly implement some high-FODMAP foods and gluten, noting any negative reactions to particular foods. I also recommended that he stewed apples to release pectin, which could help modulate his gut microbiota and improve his gut barrier function (10,11). And I advised him to introduce fermented foods into his diet, such as sauerkraut, kimchi and tempeh, due to their enhanced nutritional and functional properties and being a natural source of probiotics (12). Other changes I suggested included substituting his post-exercise cornflakes with a more nutritious post-exercise option, like a smoothie with added glutamine (discussed below). I also talked to him about using kefir or natural bio-yoghurt as a base of the smoothies, emphasising that although these were not vegan sources, they were a good way to get more natural probiotics into his diet, even if only for a short period. Flaxseeds, chia seeds and walnuts would also improve his omega-3 intake. All these changes would moreover help his overall protein intake since he was not keen on taking supplemental protein. To improve his iodine intake, I proposed a food-first approach of incorporating some seaweed into his diet. Lastly, I recommended he eliminate his pre-training morning coffee because the laxative effect of caffeine could be a contributory trigger (13).


Although John was not keen on supplements, I encouraged a prebiotic and probiotic blend with glutamine supplementation, and described the promising evidence behind these, particularly at improving gut integrity in runners (14,15). Glutamine is also relatively low in a vegan diet, which further supports the need for supplementation. As a SENr-registered nutritionist, any supplements I recommend are batch-tested through Informed-Sport.

Training and stress management

Since John was experiencing symptoms every training session and was becoming frustrated, I suggested that he reduce his running and substitute it with some cycling or swimming that are less impactful on the gut. Finally, I recommended some active restoration strategies, such as yoga and Pilates, to stimulate the parasympathetic system, attenuate any stress or anxiety, and improve his symptoms (16).


I followed-up regularly with John by email. Over the summer months, he reduced his running to allow his gut to recover. He took my recommendations on board and his symptoms reduced greatly. In September 2018, he ramped up his training again for the new season. We met for a second visit and I could immediately see that John looked more vibrant and had gained some healthy weight. He rated his gut health a seven out of ten compared to two out of ten when I had first seen him in May 2018. We knew that we were on the right track, but we dug a little bit deeper to see what else could be improved.

Follow-up interventions

John stated that he was experiencing some bloating in the mornings. After questioning him about his eating habits, he revealed that he would eat a pre-bed snack or smoothie late at night. I encouraged him to finish eating by 8pm to see if this would make any difference.

I talked to him about my light-bulb moment when we first met. The fact that his symptoms appeared a few months after turning vegan made me question whether this dietary approach was suitable for him. I encouraged John to introduce certain animal-based foods into his diet that may have additional benefits for gut health, like dairy kefir for its natural probiotics and bone broth for absorbable forms of collagen, gelatine, and key amino acids such as proline, glycine, glutamine and alanine. Kefir could be easily incorporated into his smoothies and bone broth into his cooking. I also encouraged him to introduce oily fish for omega-3s and eggs for choline – nutrients often deficient in a vegan diet. These foods would also help boost his protein intake, support recovery and bring musculoskeletal benefits. For example, a study in healthy young men showed that kefir supplementation improved glucose metabolism and attenuated the effects of muscle soreness after high-intensity exercise, which the researchers suspected may have been due to regulating antioxidant capacity (17). After discussing the evidence with John, he was keen to experiment with these foods.

As autumn was approaching, I recommended an Informed-Sport approved vitamin D supplement, and a multivitamin, thinking that since he may not be absorbing nutrients effectively, it would be a good strategy to cover all the bases. We also adjusted his glutamine timing. John had been taking it with a smoothie, often after training and then again in the evening. But I encouraged him to take it first thing in the morning on an empty stomach so it would not compete with other amino acids, and then after training sessions, especially high-intensity training or prolonged exercise periods. I also introduced some nutritional support during high-intensity or prolonged training sessions in the form of DIY sports drinks, aimed at moderating his cortisol response, preventing muscle protein breakdown and immunosuppression (18,19)

I also emphasised a ‘pre-eating routine’ – a mindful practice that helps to put the body in a relaxed state prior to eating, by taking deep breaths, chewing well and noticing every mouthful. By drinking a glass of water with lemon juice or apple cider vinegar, smelling his food and visualising taking a bite of food, this would also activate the cephalic phase of digestion, stimulating gastric secretion to aid digestion and subsequent absorption of nutrients.

Since John’s training had ramped up, I talked to him about some monitoring tools: a subjective quiz to do upon waking and a readiness-to-exercise app that would provide more objective data on his recovery and allow him to train more smartly. Since he had tried and enjoyed a yoga-based class, I encouraged him to do it more consistently.

Performance outcomes and reflections

John had done some serious racing, including the university cross-country championships, that he won, and a team relay in which they came third. Since I started working with him, he also managed to improve his 10 km PB by a second (currently 31:40). He was extremely happy with his performance and said that focusing on his gut health had a major impact. He also believed that introducing the recommended animal-based foods had made a big difference within a short time.

In November 2018, with two weeks left before the GB trials, we met again because he’d had a minor set-back in a recent race that had knocked his confidence. We also discussed key points for tapering and race day, such as eating foods he knew would not affect his gut, minimising fibre intake three days ahead of the race, and cooking his own food the night before and for breakfast on the day. Most importantly, we talked about his unrealistic sense of urgency, typical of an A-type personality, as he was doing a lot of work for university that he admitted was unnecessary because the deadlines were a month away, but he always felt the need to finish early. I encouraged him to really focus on relaxing as race day was approaching and to minimise unnecessary stress as it may exacerbate symptoms.

I illustrated this with a ‘threshold’ concept to help him understand his gut better – an imaginary line below which his symptoms are dormant, but when he added stress from training, competing and university work, he passed that line, and the symptoms would manifest and may exacerbate over time if the stress was not managed properly. I emphasised the importance of staying under the threshold by using nutrition, training and stress management strategies. It is vital that an athlete learns how to listen to their body through intuitive thinking and regular monitoring.

Unfortunately, John caught a cold which prevented him from competing on the day. However, he learned from the experience and realised that had been imposing deadlines on himself to improve (usually target races). He has now decided to listen to his body more instead of over-competing and to focus on strategies for key races like the GB trials. He also revealed that he stopped consuming kefir and bone broth just before the relapse in his last race and believed that that may have contributed as he had been doing well when consuming these regularly.

Take home message

This case study is a great example of an athlete’s health being the best ergogenic aid – a concept that Paul Ehren discussed in the Jan/Feb 2019 FSN issue (20). I focused on John’s gut health as this was the major lever that needed change. His gut health improved through a multi-faceted approach of nutrition, training and stress management strategies, which shows how we, as sports nutrition practitioners, can do so much more with an integrative view than the performance-centric view that often dominates the world of elite sport.


1) de Oliveira et al (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med. 44(1):79-85.

2) Zuhl et al (2014). Exercise regulation of intestinal tight junction proteins. Br J Sports Med. 48(12):980-986.

3) Pérez-Cobas AE et al (2012). Gut microbiota disturbance during antibiotic therapy: a multi-omic approach. Gut. 62:1591-1601.

4) Zaura E et al (2015). Same exposure but two radically different responses to antibiotics: resilience of salivary microbiome versus long-term microbial shifts in feces. mBio. 6(6):e01693-e01715.

5) Altobelli E et al (2017). Low-FODMAP diet improves irritable bowel syndrome: a meta-analysis. Nutrients. 9(9):940.

6) Monash University. FODMAPs and Irritable Bowel Syndrome. Available at: [Accessed 24 May 2018].
7) ACSM (2016). Nutrition and athletic performance. Med Sci Sports Exerc. 48(3):543-568.

8) Rogerson D (2017). Vegan diets: practical advice for athletes and exercisers. J Int Soc Sports Nutr. 13(14):36.

9) Woo KS et al (2014). Vegan diet, subnormal vitamin B12 status and cardiovascular health. Nutrients. 6(8):3259-3273.

10) Licht T et al (2010). Effects of apples and specific apple components on the cecal environment of conventional rats: role of apple pectin. BMC Microbiol. 10:13.

11) Koutsos A et al (2015). Apples and cardiovascular health – is the gut microbiota a core consideration. Nutrients. 7(6):3959-3998.

12) Marco NL et al (2017). Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. 44:94-102.

13) Rao SS et al (1998). Is coffee a colonic stimulant? Eur J Gastroenterol Hepatol. 10(2):113-118.

14) Roberts J (2016). An exploratory investigation of endotoxin levels in novice long distance triathletes, and the effects of a multi-strain probiotic/prebiotic, antioxidant intervention. Nutrients. 8(11):733.

15) Pugh J et al (2017). Glutamine supplementation reduces markers of intestinal permeability during running in the heat in a dose-dependent manner. Eur J Appl Physiol. 117:2569-2577.

16) Schumann D et al (2016). Effect of yoga in the therapy of irritable bowel syndrome: a systematic review. Clin Gastroenterol Hepatol. 14(12):1720-1731.

17) Iwasa M et al (2013). Fermented milk improves glucose metabolism in exercise-induced muscle damage in young health men. Nutrition Journal. 12:83.

18) Ihalainen JK et al (2014). Effects of carbohydrate ingestion on acute leukocyte, cortisol, and interleukin-6 response in high-intensity long-distance running. J Strength Cond Res. 28(10):2786-2792.

19) Bermon S (2017). Consensus statement immunonutrition and exercise. Exerc Immunol Rev. 23:8-50.

20) Ehren P (2019). Ergogenic aids in professional and recreational sports – a different perspective. FSN. Jan/Feb:8-10.