Sports dietary supplements: overview and effect on the gluten-sensitive athlete.
Athletes risk glycogen depletion and muscle breakdown from extensive energy expenditure. They face dehydration and electrolyte imbalances due to fluid losses during exercise. Athletes are also susceptible to many physiologic stressors. Increased sympathetic nervous system output and increased expression of multiple hormones including vasoactive intestinal polypeptide, gastrin, secretin, and motilin during exercise commonly manifest in the athlete as lower gastrointestinal distress. These physiologic changes decrease blood flow to the intestines (1), affecting GI motility and nutrient absorption. Athletes complain of transient fecal urgency, diarrhea, and abdominal cramping associated with athletic activity. These symptoms increase with harder exertion (2). They are further exacerbated by dehydration. Athletes that also complain of diarrhea without temporal association to exercise may have a concurrent lower gastrointestinal disorder further altering athletic performance such as celiac disease, inflammatory bowel disorder, or irritable bowel syndrome. Of these, celiac disease, a gluten-sensitive enteropathy, is the only common disorder that is preventable through diet modification.
It is possible to combat physiologic dysfunction related to athletic activity through the use of sports dietary supplements (SDS). When used properly, supplements may prevent glycogen depletion by maintaining energy stores during exercise and may ameliorate exercise-associated diarrhea by preventing dehydration and electrolyte imbalances (3). However, their use becomes complicated in the athlete with gluten-sensitivity or celiac disease, as the athlete has many additional risk factors for performance-altering symptoms and many sport dietary supplements contain gluten. This article explores the use of SDS, characteristics of celiac disease, dietary challenges of patients with this disease, effectiveness of a gluten-free diet, and options for dietary supplementation in the gluten-sensitive athletes.
Characteristics of Celiac Disease
Celiac disease is a common autoimmune enteropathy caused by permanent intolerance to gluten, a protein found in wheat, barley, and rye. The prevalence of celiac disease is between 1/100 to 3/500 throughout the world with highest predominance in the U.S. and Europe. The disease is classically defined by a triad of characteristic endoscopic findings, clinical symptoms, and resolution of mucosal lesions and symptoms within a few weeks to months of withdrawal of gluten-containing foods from the diet. Proximal small intestinal biopsy on endoscopy reveals villous atrophy, crypt hyperplasia, and epithelial lymphocyte infiltration of the small intestinal mucosa. Symptoms of celiac disease are classically those of malabsorption, including steatorrhea, weight loss, and deficiency of fat-soluble vitamins. In the past decade, howevr, celiac disease has become recognized as a multisystemic disorder that more commonly presents clinically through non-specific symptoms including fatigue, anemia, low-impact bone fractures, and changes in bowel habits (4), (5). Iron and folate deficiencies arc seen more commonly in people with isolated proximal small bowel disease, while those who advance to more distal disease commonly present with diarrhea (6). Another common source of diarrhea in people with celiac disease is secondary lactose intolerance, caused by decreased lactase production by the damaged villi (7).
Role of Gluten in Celiac Disease
Gluten is a complex mixture of proteins found in wheat, barley, and rye that plays an important role in the baking qualities of dough through influence on its cohesiveness, viscosity, and elasticity (8), (9). The gluten complex in wheat is divided into gluteinins, alcohol-insoluble fractions, and gliadins, alcohol-soluble fractions (4). Although gliadin peptides make up only approximately 10% of the gluten complex, it is this fraction that contains the majority of the toxic components of gluten in celiac disease. Analogous to the gladins in wheat are the hordeins in barley and secalins in rye (9), (10). Avenins in oats may also be cross-reactive in a small percentage of people with celiac disease; however, this is a matter of debate (11). These alcohol-soluble portions of gluten are resistant to digestion by gas-tric and pancreatic enzymes, and thus reach the intestinal epithelium. They exert their toxic effects in celiac disease by passing through the intestinal epithelium and causing both an innate immune response and an adaptive immune response by binding IILA-DQ2 or HLA-DQ8 on antigen presenting calls to activate CD4+ T cells (12).
Effectiveness of Gluten-Free Diet for Celiac Disease Patients
Currently, the only effective treatment for celiac disease is the life-long elimination of foods containing wheat, barley, and rye from the diet. Within two weeks of initiating a gluten-free diet, 70% of patients report improvement or elimination of their symptoms (13),(14). This clinical improvement correlates significantly with decreased endomysial antibody titers, increased mean villous height, and decreased intraepithelial lymphocyte count found on studies performed after elimination of gluten from the diet. Complications of celiac disease such as osteoporosis or decreased bone mineral density may also improve greatly on a gluten-free diet (15). Because there is potential avenin cross-reactivity and gluten-contamination of oats (16), patients are recommended to temporarily eliminate oats from the diet when first diagnosed with celiac disease. Patients newly diagnosed with celiac disease are also recommended to eliminate dairy products from the diet for the first three to six months of treatment, as longstanding celiac disease often leads to lactose intolerance (17).
In patients that do not show remission after beginning a gluten-free diet, continued symptoms are most commonly found to be due to continued ingestion of gluten-containing foods, whether intentionally or unintentionally. Barriers to maintaining a gluten-free diet include difficult-to-interpret food labels, poor palatability of gluten free foods (18), and gluten-contamination in the production of gluten-free foods. To further clarify food labels, the Food Allergen Labeling and Consumer Protection Act was passed in 2004 to mandate that the top eight allergens, including wheat, are labeled on packaged foods (19). The requirement is satisfied by either a separate "allergens" section on the label or clear use of the allergen name in the "ingredients" section. Contamination of gluten-free products is an ongoing issue due to methods of production. In the United States, most gluten-free products are produced without the use of wheat, barley, or rye. These products, however, are at risk for gluten contamination from external sources, such as shared machinery. In northern European countries, naturally gluten-containing foods such as wheat starch may also be rendered gluten-free (20) by removing the gluten-containing protein component from the starch component. These products are at risk for inherent gluten contamination if not enough of the protein component is removed, They are also at risk for external contamination. The Codex Draft Revise Standard released in 2000 set the amount of gluten contained in naturally gluten-free foods at 20 ppm and those rendered gluten-free at 200 ppm (21), (22). Although these quantities are low enough to induce remission in most patients with celiac disease, the amount of tolerable daily gluten varies greatly from one individual to another. Thus, some individuals may require even lower amounts of dietary gluten for improvement in symptoms (23).
Dietary Challenges of Athletes with Celiac Disease
Athletes with celiac disease are not only faced with the transient gastrointestinal disturbances common to many athletes, but also with baseline gluten-related diarrhea and steatorrhea due to malabsorption. These symptoms can affect athletic performance through associated abdominal cramping and dehydration. Athletic performance in individuals with celiac disease may also be affected by fatigue and increased propensity for anemia and stress fractures due to deficiencies in iron, folate, and fat-soluble vitamins (15). As athletes traditionally take in many of their daily calories in carbohydrates potentially contaminated with gluten, athletes with celiac disease have to balance increased nutritional requirements due to physical activity with predisposition for malabsorption of nutrients. Through adherence to a strict gluten-free diet, symptoms and vitamin deficiencies may be eliminated, allowing the athlete to perform at their best. This, however, requires that the athlete consume gluten-free foods that contain sufficient carbohydrate sources to match their energy needs (24).
Survey Results: Gluten-Free SDS versus Gluten-Containing SDS
In this study, sport drinks (SD), sport bars (SB), and sport gels/beans (SG) are targeted as SDS. Other SDS in the form of vitamin/mineral pills, proteins, and amino acids have been excluded. Our observation between January and June 2010 indicates that 1163 SDS are available in the U.S. market (SD= 310, SB=745, SG=108). Among these products, 716 are gluten-free (SD=276, SB=334, SG=1()6) and 447 of them contain gluten (SD=34, SB=4ll, SG=2) *. The term "gluten-free" specifically refers to the products that contain no wheat, rye or barley. In most cases, manufacturers do not guarantee that at least one of their ingredients does not come from a production line that previously processed nuts, wheat, or dairy. This fact can be applied to their supply chains, as well. In our study of products, "Nutrition Fact Labels" were the main source for indicating the presence of gluten in sport bars. For other products, in most cases, labels do not indicate the presence of gluten. Therefore, the information had to be obtained by e-mailing or calling (he manufacturers or searching their websites.
Athletes require additional fluid to cover sweat losses and additional energy to fuel physical activity. SDS can be used to fulfill these needs before, during, and after sport activities. Despite numerous sources of information being available and huge demand for SDS, many athletes use these products without a full understanding or evaluation of the potential benefits and risks associated with their use, and without consultation with sports nutrition professionals. The lack of knowledge about SDS ingredients and effects can contribute to lower gastrointestinal problems which are common in athletes and as a result of the high prevalence of celiac disease throughout the world, this disease has been targeted as one of the possible causes of diarrhea in athletes. Therefore, it is important for health and nutrition professionals to identify and treat nutritional challenges that impact the health and performance of athletes. This study concludes that celiac disease patients have a wide variety of choices among gluten-free SDS. Interestingly, 61.56% of SDS available in the U.S. market are gluten-free; however, SDS labeled as gluten-free are at risk for gluten contamination from external sources.
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* For a comprehensive listing of the SDS products reviewed in this study, go to www.amaasportsmed.org and click on AMAA Journal in the navigation bar.
Sara Keihanian, MD; Kristen Burke; and John Levey, MD, MBA; University of Massachusetts School of Medicine and University of Massachusetts/Memorial Healthcare
Address for Correspondence: John Levey, MD, MBA; University of Massachusetts School of Medicine; 55 N. Lake Avenue; Worcester, MA 01655; E-mail: firstname.lastname@example.org; Tel: 508-334-3833; Fax: 508-856-3981.
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|Author:||Keihanian, Sara; Burke, Kristen; Levey, John|
|Article Type:||Clinical report|
|Date:||Sep 22, 2010|
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