Gastrointestinal symptoms (GIS) are widely reported in athletes participating in prolonged endurance events including; cyclists, triathletes and marathon runners, although there is a large estimated range of between 4–96% of participants affected [1
]. These symptoms can have a number of aetiologies, including underlying pathology such as inflammatory bowel disease, the physiological changes that occur with exercise such as the reduction of splanchnic blood flow, changes to the physiology of digestion and transit, and the gut–brain axis [1
]. Numerous potential factors may explain the large variance in reported symptoms such as the mode, duration or intensity of exercise, environmental conditions, nutritional intake, type of assessment tool, and method used to classify a “symptom”. For example, studies have used 4, 9, 10, and 11-point scales, each with differing vernacular, to quantify GIS [2
]. Positive responses, of any magnitude, including those that do not affect performance, could be seen to overestimate the prevalence of symptoms, or may lead to erroneous conclusions regarding symptom severity. For example, studies that have reported data for GIS in marathon runners without acknowledging severity have shown prevalence rates of 52% and 71% [6
]. Contrarily, when symptoms were described as ‘moderate’ or ‘serious’ in severity, prevalence has been reported as 4–7% [2
]. Furthermore, symptom severity in the scales used is a subjective measure and not further quantified by, for example, duration or impact on performance. It is, therefore, clear that there is a need to better assess both the frequency and severity of GIS during a marathon race.
One potential cause of GIS during marathon running is nutritional intake before and/or during the race. Carbohydrate (CHO) intake in both the days before and during endurance exercise has been shown to be beneficial to performance [8
] yet there appears to be an association between carbohydrate intake during endurance exercise and GIS [10
]. The mechanisms through which this may occur include potential malabsorption leading to luminal distension, delayed gastric emptying and gas production [13
]. It has been shown that reducing GIS associated with CHO intake during exercise was associated with improvements in performance [10
]. However, to date, there has been little research into habitual dietary intake of recreational marathon runners, and their association with GIS during a race. The aim of the present study was to document the dietary intake and prevalence and severity of GIS during training in the week before a marathon and during a marathon and to investigate any association between them.
Mean time to complete the marathon in each race was 260 (176–361) and 236 (183–278) min, for the Liverpool and Dublin marathon, respectively. Training data are shown in Table 1
, and nutritional data are shown in Table 2
and Table 3
shows the prevalence of any symptoms (score ≥2) and any moderate symptoms (score ≥4). From both races, 41% and 47% of participants reported at least one moderate symptom during the previous 7 days, while 30% and 20% reported experiencing moderate symptoms during the race for Liverpool and Dublin marathon respectively.
To identify potential associative factors, GIS scores were summed to give lower, upper and total GIS scores. Correlations between symptoms during the race and all nutritional factors were low and insignificant (r < 0.20, p > 0.05). There were significant correlations between symptoms in the 7 days prior to the race and during the race for total GIS score (r = 0.510, p < 0.001), upper GIS score (r = 0.346, p = 0.001) and lower GIS score (r = 0.483, p < 0.001).
The current study assessed the incidence and severity of numerous GIS, using a previously validated questionnaire to document the dietary intake and GIS during training in the week before a marathon and during a marathon in order to explore potential predictive factors of GIS. Our data indicate that there is a significant prevalence of moderate GIS in the week leading to a marathon race, and during the race amongst recreational runners. We show that 42% of participants reported moderate GIS in the 7 days prior to the marathon and 27% reported moderate symptoms during the marathon with most common symptoms being flatus (16%) during training, and nausea (8%) during the marathon race. However, it was found that there was no association between nutritional intake and symptoms, neither in the 24 h prior to, during the meal before, nor during the race.
Gastrointestinal symptoms during endurance competitions have been previously reported by 4–96% of participants [1
]. Differences between studies could be due to a number of factors such as exercise intensity or duration, and environmental temperatures, which have been shown to exacerbate gastrointestinal damage and increase symptoms [1
]. Variances may also arise from the questionnaires used, the symptoms that are included, and the criteria for classifying a symptom. Studies that have reported data for GIS in marathon runners, without acknowledging severity, have shown prevalence rates of 52% and 71% [6
], while ‘moderate’ or ‘serious’ GIS prevalence has been reported as 4–7% [2
]. In the present study, 70% of participants reported having any symptoms, while only 27% had symptoms recorded as moderate or worse, with nausea being the most common (12% of all runners). This highlights the need to differentiate symptom severity within studies, as well as the specific symptom, as these may have different aetiologies, and therefore require different interventions for attenuation. Future studies should ensure pathology is excluded (bloods and faecal calprotectin, endoscopy etc.) and psychological factors, along with validating symptoms against Rome III or IV diagnostic criteria for irritable bowel syndrome. We have, however, made some distinction between exertion related symptoms and nutritional factors.
Gastrointestinal symptoms have been shown to relate to higher CHO intake, higher fat intake, and, in particular, lower fluid consumption during ultra-distance events of longer duration [2
]. However, this has not been as clear in marathon running or events of shorter durations [2
]. Here, there was no correlation between total, upper or lower GIS scores and any nutritional factor recorded. This includes dietary intake in the 24 h prior to the race, breakfast on race-day, or in-race nutrition. The difference may be due to the duration of the event. For example, it has been shown that the majority of symptoms during ultra-distance running events did not occur until after 50 km of running and coincided with greater reductions in body weight, attributed to dehydration [4
]. If euhydration is maintained, GIS may be less prevalent, as has been found in events lasting even up to and beyond 24 h [24
]. Longer duration events, and therefore greater total dietary intake, has also been proposed to increase the likelihood of CHO malabsorption [10
]. However, with the recorded CHO intakes during the marathon (mean of 0.4 g·min−1
), this was unlikely to be seen here. While not the primary aim of the present study, it should be noted that the mean values for CHO intake both before and during the race were below those recommended for marathon performance [26
]. This nutritional intake data is in close agreement with previous studies in marathon runners [27
]. Recreational runners’ performance could therefore be improved with appropriate CHO intake. As no association was observed here between nutritional intake and GIS, some other factors, not assessed here may contribute to the prevalence of GIS found.
Gastrointestinal symptoms are often more prevalent during marathon running and other endurance events in individuals with a history of symptoms [2
]. The results here showed a large correlation between symptom scores during the 7 days before the race and during the race. This corroborates previous study findings and may be due to a number of factors. These individuals may consistently be those becoming dehydrated, they may have some underlying pathology, or they may experience greater levels of stress and/or anxiety which has been shown to increase gastrointestinal symptomology [20
A limitation of the present study is the use of food diaries to analyse nutritional habits, and indeed, previous research has shown a potential under-reporting effect of up to 20% [29
]. It is possible that macronutrient, fibre, and fluid intakes reported have been under-estimated. However, total calories and CHO intake reported here are in close agreement with previous studies in marathon runners [27
]. It should also be noted that a reduction in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) intake has recently been shown to alleviate GIS in endurance athletes [30
]. However, FODMAP content was not quantified here, and this may have been a factor associated with symptoms seen in the current study. Additionally, both marathon races included here had over 20,000 participants combined, yet only 216 runners registered to participate, with 96 of these runners completing the online questionnaires to sufficient detail to be included in the dataset. Therefore, the results could be liable to non-response bias [31
] raising the possibility that the data are exaggerating the prevalence of GIS, particularly if those who experience symptoms had more interest in the research project, and therefore were more likely to participate in a related study. Finally, as with any study of an observational nature, there are other confounding variables, otherwise not accounted for, whilst it is also difficult to draw any conclusions of cause-and-effect.