This nutritional study aimed to investigate the perceived effect of acute FODMAP intake on GI symptom severity and ability to exercise in recreational athletes under free-living conditions. Whilst the clinical effectiveness of a LOW FODMAP diet in treating IBS is established in the literature, research into the potential therapeutic effects in otherwise healthy, recreational athletes is limited. The main findings from the current study revealed that short-term LOW FODMAP intake significantly improved exercise-related GI symptoms in 69% of participants. These results support recent observations demonstrating reductions in daily GI symptoms in trained athletes on a short-term (6-day) LOW FODMAP diet, as well as reduced GI symptom severity in case studies of a male and female runner. Consistency between these findings infers that both recreational and more trained athletes may benefit from self-prescribed LOW FODMAP approaches in the short-term, providing there is compliance with food choices. This may have implications for longer-term FODMAP strategies during sustained training periods, which may provide adjunct nutritional support in maintaining training volume and/or intensity particularly in symptomatic individuals who suffer from GI distress with exercise.
Whilst a LOW FODMAP approach appeared to result in improved scores for most individual symptoms, only responses to perceived pain and bloating were significantly different between conditions following the dietary interventions. This suggests that whilst an improvement in overall GI symptom severity may reflect accumulated reductions in individual symptom responses, the effects of a short-term LOW FODMAP diet may, in fact, be specific. The reported improvement in perceived pain, in conjunction with reduced experiences of bloating whilst on a LOW FODMAP diet, is likely explained by a reduction in intestinal water volume and gas production. Strategies to reduce or minimize such GI symptoms may be important for recreational athletes, especially considering the reported negative impact on exercise training and/ or performance. However, based on the wide inter-individual responses observed across conditions, such findings should be interpreted with caution.
An interesting observation from the current study was the improved perception of exercise frequency and intensity from participants whilst undertaking the LOW FODMAP approach. Although this only reflected perceived changes in the short-term (7 days), this may have implications for sustained approaches where training routines may be disrupted (including volume and intensity) due to GI-related issues. Participants were requested to maintain their typical training routine throughout the study to assess whether perceived changes (in frequency, training duration or intensity) were related to the dietary intervention. Whilst a significant effect was observed for improved perception of exercise frequency and intensity following a LOW FODMAP approach, this only occurred in 25 and 38% of the participants respectively. Only one other study appears to have attempted to standardize training sessions (albeit 2 sessions in a 6-day period) whilst participants undertook an acute LOW FODMAP or HIGH FODMAP diet. In this study, daily GI symptoms for flatulence, urge to defecate and diarrhea was reportedly improved in the LOW FODMAP condition. However, the assessment of participants’ perception of training session ability in relation to the dietary approach was not considered. Further research to establish training related benefits of a LOW FODMAP strategy, particularly with symptomatic individuals, is therefore warranted.
Moderate to high-intensity exercise impacts on gastric emptying, GI transit and intestinal absorption due to GI hypoperfusion and ischemia. Provocation of luminal tight junction proteins (e.g. Claudine and occluding) through increased expression of phosphorylation enzymes, reactive oxygen species (ROS) activity, and cytokine mediators may lead to acute GI permeability and Paracellular transport. Although transient, acute GI disruption may exacerbate nutrient malabsorption, as well as provoke delayed systemic immune responses. Increased residual HIGH FODMAP GI content as a result of malabsorption, along with increased delivery of fluid to the colon and reduced GI motility could synergistically impact on the perceived severity of symptoms, including acute or transient pain. This may limit the intensity of exercise training, particularly in symptomatic or hypersensitive individuals. The reduction in pain observed in this study, along with an improved perception of flatulence and bloating symptoms within-group, indicates that lowering FODMAPs in the diet may support exercise training. Mechanistically, a reduction in fluid re-uptake across the GI epithelia, leading to less fluid and gas build-up pre- or during exercise in response to daily or more habitual LOW FODMAP approaches may assist with sustained exercise tolerance.
In connection with perceived symptom changes, this study also investigated whether a short-term FODMAP approach impacted on basal GI damage via assessment of I-FABP. Whilst it was hypothesized that a HIGH FODMAP diet may lead to an elevated residual level of I-FABP following the short-term intervention, no significant differences were observed within or between conditions. Therefore, even though a HIGH FODMAP approach may have resulted in an increased perception of symptom severity, disruption of the epithelial barrier in response to dietary modifications was not evident. Previous research has demonstrated that splanchnic hypoperfusion in response to acute, moderate exercise resulted in elevated I-FABP from 309 ± 46 pg·ml− 1 to 615 ± 118 pg·ml− 1 in healthy, male volunteers, which rapidly returned to baseline concentrations within minutes of recovery. I-FABP is a sensitive marker of small intestinal cell damage. However, rapid changes as observed in the previous study indicate that GI damage is highly transient, and possibly only in response to exercise-based hypoperfusion, which may explain the lack of significant residual findings under resting conditions in the current study. Assessment of I-FABP and/or GI permeability (e.g. urinary lactulose: rhamnose evaluation) in response to daily bouts of exercise in conjunction with a FODMAP approach may, however, provide a mechanistic understanding of the potential benefits of a LOW FODMAP diet.
A limitation to the current study observed when implementing a LOW FODMAP diet in free-living conditions was that participants tended to consume fewer calories compared to both habitual and HIGH FODMAP intakes, albeit non-significant. Taking into consideration methodological constraints in maintaining a weighed food diary, this observation was supported by a significant reduction in carbohydrate intake to achieve LOW FODMAP adherence. This finding is consistent with a case study of a female athlete competing in a Multistage Ultramarathon, which reported that whilst following a LOW FODMAP approach total daily energy intake did not meet estimated energy requirements. Upon further investigation, suboptimal carbohydrate intake rather than protein and fat was observed.
Similar findings have been reported elsewhere, in which 29% of participants reported acute weight loss whilst on a LOW FODMAP approach in free-living conditions. Many carbohydrate-rich foods typically consumed by active individuals (e.g. pasta, cereals, bread, energy drinks) are HIGH FODMAP, whereas alternative food sources (e.g. rice, corn) may be less palatable or more difficult to substitute. Indeed, in the previous study, participants cited that LOW FODMAP approaches were either too complicated, expensive, or did not enjoy the overall taste as reasons for not sustaining the diet. The potentially restrictive or limiting nature of food choices on a LOW FODMAP diet could, therefore, outweigh GI symptom benefits in the longer term due to weight loss, lethargy, fatigue, perceived effort, cost and/or enjoyment. Furthermore, a sustained energy/carbohydrate reduction in the longer term could also impact on training maintenance and recovery adaptations, and lead to unintended reduced nutrient availability.
However, the finding that acute dietary FODMAP manipulation positively impacted on overall GI symptom severity has pertinent implications for active individuals, particularly those more symptomatic or hypersensitive. Future research should consider whether there is a threshold of symptom severity in the context of exercise above which individuals may benefit from a LOW FODMAP nutritional approach. There is also the need to establish the minimum intervention length required to alleviate GI symptoms in both recreational and trained athletes; as well as how long interventions can be sustained or indeed whether a FODMAP approach can impact on prolonged training periods. This is especially important considering the finding that carbohydrate intake was reduced on the LOW FODMAP diet in free-living conditions and the known importance of carbohydrates in fuelling regular exercise. Finally, whilst a LOW FODMAP diet is known to significantly affect the gut microflora composition, the consequences of prolonged LOW FODMAP intake on other types of physical activity, particularly those of a high-intensity or intermittent nature, has yet to be determined.
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