Exploring the practises and effects of gluten-free and low FODMAP diets in noncoeliac athletes

Background and Aims Exercise-associated gastrointestinal (GI) symptoms are widespread and estimated to occur in 30-50% of endurance athletes. GI symptoms are multi-factorial but primarily caused by physiological, mechanical and/or nutritional triggers. Symptoms generally occur during exercise or within the few hours following exercise. Gluten is touted by many to be detrimental to GI health in athletes particularly with a compromised gut barrier caused by reduced splanchnic blood flow, which most commonly occurs during higher exercise intensities. It is suggested that exercise-induced injury to the gut barrier could in turn increase susceptibility to dietary triggers, such as gluten. Gluten is further perceived to elicit undesirable proinflammatory responses in healthy athletes, partially through compromised gut epithelial barrier function, allowing the passage of gluten peptides or the interaction of these peptides with tight junction proteins. However, these theories alongside the overall idea that a glutenfree diet (GFD) provides an ergogenic benefit have yet to be substantiated. Athletes persistently explore dietary strategies perceived to offer ergogenic benefits or beneficial impacts on parameters influencing performance, such as reducing GI symptoms. There has been an explosion in the prevalence and use of gluten-free products in recent years, which is exacerbated by unsubstantiated commercial health and sport performance claims. This has led to numerous athletes touting a gluten-free lifestyle as the secret to their success. It is well known that a GFD is necessary for the treatment of clinical conditions such as coeliac disease or noncoeliac gluten (wheat) sensitivity (NCGS). However, anecdotal reports suggest that many athletes believe a GFD directly improves exercise performance and parameters influencing performance, particularly GI symptoms as well as inflammation and immune health. Dietary changes may occur alongside the avoidance of gluten-containing foods that could influence health parameters or GI symptoms. A predominant dietary change that occurs subsequent to eating a GFD also includes a reduction in the intake of short-chain carbohydrates, otherwise known as fermentable, oligo-, di-, monosaccharides and polyols (FODMAPs). Significant FODMAP reduction may actually modulate GI symptoms, and not necessarily the gluten itself. Given the absence of peer-reviewed data on the effects of either gluten or FODMAPs on athlete performance, the studies that comprise this thesis were first aimed to understand and quantify the prevalence of GFD adherence, and relatedly, high FODMAP food avoidance among noncoeliac athletes (NCA). A second step was to undertake intervention studies to investigate the efficacy of these diets on GI symptoms, performance and related parameters in an athletic population. Methods and Results An electronic-based questionnaire (n=910) was distributed internationally to athletes to determine athlete-specific GFD and high FODMAP avoidance food behaviours and beliefs. Specifically, this questionnaire was designed to evaluate GFD practises, demographics, experiences, and sources of dietary recommendation and information. Our initial findings established that 41% of NCAs followed a GFD at least 50% of the time. Negative GI symptoms (e.g. diarrhoea, bloating) were the most highly reported indicators believed to be triggered by gluten with 84% of respondents indicating symptom improvement with gluten-removal. Athletes adhering to a GFD also perceived a GFD to improve body composition for sport (74.4%), reduce inflammation (73.3%), decrease GI distress (61.1%), and improve exercise performance (56.3%). Self-diagnosed gluten-related conditions were the primary reason for adopting a GFD with non-medical dietary prescription and advice from coaches/other athletes reported as the most common source of GFD information. Given the high uptake of a GFD in athletes and the belief that a GFD improved exercise performance, GI health and wellbeing, the next study within this thesis aimed to investigate the effects of a GFD on performance in endurance-based NCA. Thirteen competitive NCA (endurance cyclists) were allocated to a 7-day gluten-containing diet (GCD) or GFD (16 g gluten.day\\(^{-1}\\)) using a controlled, double-blind, crossover intervention design. During each diet, cyclists completed GI questionnaires (daily and during exercise), the Daily Analysis of Life Demand for Athletes (DALDA) and an exercise test on day seven of each dietary period. Blood samples were taken pre-exercise, after a 45-minute steady state exercise bout at 70% Wmax and following a 15-minute time trial (TT) to measure acute intestinal injury and inflammatory markers. Exercise and dietary intake was tightly controlled and replicated during each dietary period. A GFD had no beneficial or negative effect on 15-minute cycling TT performance (GCD 245±53 and GFD 245±55 kJ). GI symptoms, DALDA evaluation and biomarkers of acute epithelial injury and systemic inflammation were also similar in the GCD and GFD periods. The GFD intervention did not show a GFD to be ergogenic; however, when a GFD is adopted, FODMAPs may be reduced. The low rates of GI symptoms reported in our initial study may have been confounded by a reduction in fructans on both trials, which are part of the FODMAPs family. Initial findings led to subsequent studies investigating FODMAP avoidance or reduction in NCA. First, athletes' dietary behaviours regarding FODMAPs were established via FODMAP-specific questions in the preliminary questionnaire-based study. Offending foods that happened to be part of the FODMAP family were quantified as a popular strategy employed by 51% of NCA to reduce GI symptoms with 83% of this group reporting symptom improvement. To examine the effects of short-chain carbohydrate restriction on GI symptoms, a short-term low FODMAP dietary intervention was conducted utilizing a case-study methodology in a multisport athlete with persistent exercise-associated GI distress. A 6-day low FODMAP compared to a habitual high FODMAP diet was implemented and the athlete was evaluated for GI symptoms and DALDA scores indicating 'worse than normal.' On each day of the intervention a measurable reduction, from symptom severity scores of 0-9 to 0, in exercise and daily GI symptoms was observed. DALDA scores remained stable across the habitual and intervention periods. The GI symptom improvement in this athlete suggested the necessity for a larger crossover intervention to further explore the use of a FODMAP restricted diet as a tool to reduce GI distress in healthy symptomatic endurance athletes. To further explore the potential of a low FODMAPs intervention to reduce GI symptoms, a larger preliminary trial was conducted. GI symptoms and perceptual wellbeing were assessed during a high FODMAP vs. low FODMAP diet in runners (n=11) with persistent exerciseassociated GI symptoms, but no diagnosed functional gastrointestinal disorder or food intolerance. Runners were randomized to low (<9 g FODMAP.day\\(^{-1}\\)) and high FODMAP (>20 g FODMAP.day\\(^{-1}\\)) dietary periods of 6-days each with prescribed strenuous running sessions completed on day-4 and day-5 and a single day washout before crossing over to the other diet. Exercise and diet were replicated with study meals and snacks provided alongside suitable low or high FODMAP food choices. During each dietary trial runners recorded dietary intake and exercise and completed electronic GI symptom and DALDA questionnaires. Large variability in GI symptoms was apparent with no statistical difference in exercise GI symptom frequency or severity and DALDA score. While exercise GI symptoms were not different, daily GI symptoms were lower each day of the low FODMAP dietary period. Short-term FODMAP reduction may be a novel tool in improve daily GI symptoms in healthy runners with exerciseassociated GI distress. Future work in this area should incorporate exercise protocols with higher intensity and longer duration to better assess the impact of this diet on GI symptoms occurring during exercise. Conclusions This progressive work has quantified widespread adherence to a GFD amongst NCA. Although, many NCA adhere to a GFD due to beliefs underpinned by unsubstantiated health, GI and performance benefits, a short-term GFD was not found to have a beneficial (or negative) effect on performance, GI health, systemic inflammation or overall wellbeing. FODMAP intake may be consequently reduced with a GFD and is proposed to modulate GI symptoms, rather than gluten itself. Relatedly, elimination of high FODMAP foods were found to be a common dietary strategy employed by athletes aimed at attenuating GI symptoms with high rates of self-reported success. Results from our successive intervention studies showed improvement in GI symptoms with elimination of high FODMAP foods. Based on these findings, FODMAP manipulation, rather than gluten-elimination, may be a more successful and novel intervention to consider for the sport nutrition practitioner's toolbox for management of GI distress in athletes. A practitioner supported systematic and individualized approach will be essential for the potentially successful implementation of these dietary approaches.