Acute Topics in Sport Nutrition

M. Lamprecht

• Editore: S. Karger
• Anno: 2012
• ISBN:
  9783805599931
• Argomento: Medicina
• Categoria: Endocrinología y metabolismo

In high-performance sport an optimal diet and nutritional interventions can make the difference between victory and defeat. In recent years, sport nutrition research has increased. This publication provides scientifically-based information with regard to the bioefficacy of trendy sport supplements and dietary approaches off the mainstream. International experts in the specific fields inform and clarify under which circumstances the application of certain supplements and nutritional interventions would be beneficial, either for the performance or health of the athletes. A broad spectrum of recent topics in sport nutrition is provided: selected sport supplements aside of mainstream, nutritional interventions and athlete's health, hydration and fluid balance and current aspects in exercise and exercise recovery. Finally, the publication concludes with recent information about the risk of supplementation and inadvertent doping. The book will be of benefit to sport physicians and scientists, nutritionists, coaches and athletes, as well as to the sport nutrition trade and related industries.

Nutritional Interventions and Athlete’s Health

Lamprecht M (ed): Acute Topics in Sport Nutrition.
Med Sport Sci. Basel, Karger, 2013, vol 59, pp 47–56

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Exercise, Intestinal Barrier Dysfunction and Probiotic Supplementation

Manfred Lamprecht^a,b · Anita Frauwallner^c,d

^aInstitute of Physiological Chemistry, Center for Physiological Medicine, Medical University of Graz, and ^bInstitute of Nutrient Research and Sport Nutrition, Graz, and ^cAustrian Society of Probiotic Medicine, Vienna, and ^dInstitut Allergosan, Forschungs- und Vertriebs GmbH, Graz, Austria

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Abstract

Athletes exposed to high-intensity exercise show an increased occurrence of gastrointestinal (GI) symptoms like cramps, diarrhea, bloating, nausea, and bleeding. These problems have been associated with alterations in intestinal permeability and decreased gut barrier function. The increased GI permeability, a so-called ‘leaky gut’, also leads to endotoxemia, and results in increased susceptibility to infectious and autoimmune diseases, due to absorption of pathogens/toxins into tissue and the bloodstream. Key components that determine intestinal barrier function and GI permeability are tight junctions, protein structures located in the paracellular channels between epithelial cells of the intestinal wall. The integrity of tight junctions depends on sophisticated interactions between the gut residents and their expressed substances, the intestinal epithelial cell metabolism and the activities of the gut-associated lymphoid tissue. Probiotic supplements are an upcoming group of nutraceuticals that could offer positive effects on athlete’s gut and entire health. Some results demonstrate promising benefits for probiotic use on the athlete’s immune system. There is also evidence that probiotic supplementation can beneficially influence intestinal barrier integrity in acute diseases. With regard to exercise-induced GI permeability problems, there is still a lack of studies with appropriate data and a gap to understand the underlying mechanisms to support such health beneficial statements implicitly. This article refers (i) to exercise-induced intestinal barrier dysfunction, (ii) provides suggestions to estimate increased gut barrier permeability in athletes, and (iii) discusses the potential of probiotic supplementation to counteract an exercise-induced leaky gut.

Copyright © 2012 S. Karger AG, Basel

In performance sports there is a high prevalence of gastrointestinal (GI) complaints, especially among endurance athletes like runners and triathletes [1]. These problems are attributed to changed blood flow that is shunted from the viscera to skeletal muscle or the heart [2]. Symptoms described are nausea, stomach and intestinal cramps, vomiting and diarrhea. An increased permeability of the GI epithelial wall precedes and accompanies these symptoms. This so-called ‘leaky gut’ leads to endotoxemia, and results in increased susceptibility to infectious and autoimmune diseases, due to absorption of pathogens/toxins into tissue and the bloodstream [3–5].

Probiotic bacteria are described as live microorganisms that beneficially modulate microflora and health of the host [6]. In the last few years they have become increasingly popular as nutritional supplements, especially to achieve reduction of GI complaints and common infectious illnesses. In sports and exercise, there is some evidence for probiotics’ potential to reduce the incidence and severity of respiratory tract infections [7, 8] and to shorten the duration of GI symptoms in trained athletes [9]. Other studies report attenuation of exercise-induced increase in pro- and anti-inflammatory cytokines after 11 weeks [10] and increased plasma antioxidant levels after 4 weeks of probiotic supplementation [11].

The effects of probiotics on intestinal barrier integrity are not sufficiently elucidated and even less in the framework of sports and exercise. Our research using PubMed did not reveal any study reporting the effects of probiotic supplementation on exercise-induced gut barrier dysfunction, although such nutritional solutions could be of reasonable practical relevance for athletes.

This lack in sport nutrition research encouraged us to write this article dealing with exercise-induced intestinal barrier dysfunction and discussing the potential of probiotic supplementation to counteract the associated problems.

Intestinal Barrier

The intestinal mucosa is the largest boundary layer between the surrounding world and the internal human milieu representing a surface area similar to the size of a soccer field [12]. The ability to control and balance the invasion of harmful content from the intestinal lumen into the internal organism is called intestinal barrier function. This barrier can roughly be divided into three parts where (i) luminal bacteria, (ii) epithelial cells, and (iii) the gut-associated lymphoid tissue (GALT) work in concert to prevent potential pathogens from translocation from the lumen into the internal milieu [13] (fig. 1).

(i) Most bacteria within the GI tract are killed by bactericidal salivary lysozyme, gastric acid and pepsin, bile salts and Paneth cell-derived defensins [14]. If bacteria survive this security system they are combated by the commensal microbiota to inhibit their colonization. Commensal bacteria produce antimicrobial substances to kill competitor strains, they induce pH modification of the luminal content and act competitively to get nutrients required for bacterial growth [15].

(ii) The epithelial layer covers the inner surface of the intestine. These epithelial cells are connected to each other by junctional complexes that consist of tight junctions, adherens junctions and desmosomes. The tight junctions are the most important physical barrier protein structures that allow selective passage of ions and small molecules and they form a tight barrier to protein-sized molecules and bacteria [16]. Beside the physical barrier function, the epithelial layer is also responsible for the communication between the luminal contents and the basolateral located gut-associated lymphoid tissue. Epithelial cells are equipped with Toll-like receptors, which are capable of recognizing both commensal and pathogenic bacteria and their toxic products such as lipopolysaccharides. When detected by Toll-like receptors, potential pathogens induce proinflammatory mechanisms within epithelial cells, leading to an immune response directed against these intruders [17].

(iii) The GALT is the largest immune organ in the body and most of it is organized in structures named Peyer’s patches. The covering epithelium of the Peyer’s patches contains M-cells, which possess the ability to take up antigens and bacteria from the intestinal lumen through endocytosis and deliver these to antigen-presenting cells and lymphocytes located in the basolateral side of the Peyer’s patches [18]. Below the epithelial layer, dendritic cells are mainly responsible for the decision to either ignore or to respond to invading antigens and bacteria [13]. They orchestrate immune responses by instructing T-cells to express pro- or anti-inflammatory cytokines like IL-12 or IL-10.

Fig. 1. Three levels of barrier function (from F. Lutgendorff: Defending the barrier [13]): (1) Luminal commensal bacteria prevent colonization of potential pathogens by producing antibacterial substances and by forming competition for nutrients required for bacterial growth of pathogenic microorganisms. (2) Epithelial cell form the most obvious physical barrier and are interconnected by means of tight junctions. Recognition of pathogens and commensal bacteria is mediated through differential activation of Toll-like receptors (TLRs). (3) Upon recognition of potential pathogens by TLRs, epithelial cells can respond with an innate reaction to activate nuclear factor NF-κB. Dendritic cells (DCs) are key players in the adaptive immune response and reside primarily within the subepithelial dome (SED) of Peyer’s patches, which is covered with specialized M-cells. Once potential pathogens are recognized by DCs, these respond with the production of interleukin-12, skewing the T-cell response towards a proinflammatory Th1-type response.

Exercise and Disturbed Intestinal Barrier Function

Strenuous exercise can lead to functional disturbances in the complex barrier system of the intestinal wall. The main causative base that triggers decreased barrier function during exercise might be a changed blood flow, which is shunted from the viscera to skeletal muscle and the heart [2]. The higher the intensity and the longer the duration of the conducted exercise model, the more distinctly this changed blood flow occurs in the gut, heart and skeletal muscle regions. A mesenteric undersupply with blood, oxygen, nutrients and the insufficient removal of metabolites leads to a metabolic disturbance in the intestinal barrier area including hypoperfusion/ischemia-induced pH decrease which in turn results in oxidative stress. Also, the increased production of catecholamines during intensive exercise and their subsequent autoxidation may contribute to disturbing the mesenteric redox balance. The overwhelming production of reactive oxygen and nitrogen species (RONS), including hydrogen peroxide, results in oxidized and damaged biomolecules, changed cell communication pathways and inflammatory processes induced by cytokines from GALT-based immune cells. Subsequently, tight junction proteins and epithelial cell membranes are some of the affected structures that change and/or lose their integrity [19, 20]. In addition, there might be some other exercise-induced disturbances in the mesenteric area like water availability (dehydration), changed osmolality and gut motility that can contribute to a decreased intestinal barrier integrity [21].

Decreased tight junction competency leads to a ‘leak’ in the paracellular absorption route that enables p...