Gut distress is common among athletes, particularly endurance athletes. About 30-50 percent of athletes report gut distress symptoms that include bloating, abdominal discomfort, nausea, vomiting and diarrhea (1).
Although gut distress may affect performance outcomes, it may also affect recovery ability. Gut, or gastrointestinal (GI), distress can be caused by a variety of underlying issues ranging from food intolerances and GI disease to suboptimal nutrient timing and volume intolerance. With so many different root causes of gut distress, it is not uncommon for a coach or athlete to rapidly reach an incorrect conclusion regarding the cause behind an athlete’s gut distress. As a result, those struggling with gut distress are encouraged to work with a certified professional to help identify health conditions and dietary habits that might be contributing to gut distress symptoms.
In the United States, GI diseases are estimated to affect 11 percent of the population (2). Examples of gut abnormalities include Inflammatory Bowel Syndrome (IBS), gastritis, Celiac Disease, Diverticulitis, and gastroparesis among others. Although the pathophysiology of GI conditions differs from one to another, these conditions share a common trait, which is their interference with digestion and absorption of nutrients. The way that these conditions affect digestion and absorption can often be attributed to lack of enzyme production, immunological responses, inflammation, and/or poor nutrient timing.
For example, lactose intolerance, a condition that affects 68 percent of individuals, occurs when the intestinal lining produces insufficient enzymes to breakdown “lactose,” a sugar found in dairy products (3). Consequently, the undigested lactose molecule is fermented causing flatulence, abdominal pain and diarrhea. Conditions such as Celiac disease, on the other hand, provides us with a suitable example of an immunological response to the ingestion of a particular food. When an individual has Celiac disease, consuming gluten, a protein found in wheat, rye and barley, causes an immunological response that targets your small intestines, in particular your villi, causing abdominal pain, diarrhea, and bloating (4). Both Celiac disease and lactose intolerance can be treated by removing the food item(s) responsible for gut distress symptoms.
However, conditions such as IBS, which has no clear etiology and treatment, offer much more complicated challenges. IBS is a condition which is diagnosed based off of an individual’s reported symptoms leaving medical providers with no clear root problem to address. Often it is recommended to eliminate foods containing FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) from the diet, although with no guaranteed alleviation of symptoms (5). With help from your medical provider, an appropriate course of action can be taken in treating IBS symptoms. This is especially important given simply removing FODMAPs without strong rationale can lead to more symptoms as fermentable carbohydrates have beneficial effects on gut microbiota. Simply removing FODMAPs can cause more harm than good
All three of these conditions require medical diagnosis from medical providers. As a result, it is important to seek help from medical providers if symptoms are present and interfering with activities of daily living. As an athlete, it is important to familiarize oneself with foods that they can and can’t tolerate given that individual responses to food vary significantly from person to person.
Gut Intolerance and Exercise
Although gut diseases can cause gut distress during exercise, even a healthy athlete can experience what is called “exercise-induced gut distress.” When engaging in physical activity, blood flow is shifted away from the GI tract towards active muscles and the lungs. Concurrently, gastric emptying is slowed down causing food to sit in the stomach longer than normal. As a result, consideration of nutrient timing, nutrient composition and food volume is an important factor to consider. Given nutrients such as protein, fiber and fat slow down digestion, it is recommended to consume foods containing these nutrients 2-4 hours before exercise. Opting for simple carbohydrates before exercise is more favorable. It is well recognized that carbohydrates are the preferred fuel source for energy expenditure in the body.
In fact, a foundational sports nutrition principle for athletes is “fueling” for exercise with simple carbohydrates (e.g., sports drinks, fruits, candy), given the rapid absorption and subsequent utilization during exercise. General recommendations suggest having 1-4 g/kg of carbohydrates 1-4 hours before exercise depending on intensity and duration of exercise, with the higher range catering towards longer and more intense activities while the lower range catering to shorter and less intense activities (6).
However, although crucial to optimizing an athlete’s performance, simple carbohydrate intake may also induce exercise-induced gut distress. This is especially prominent in endurance sports in which athletes engage in extended durations of exercise requiring intra-exercise fueling (7). As a result, athletes may be left weighing the benefits of carbohydrate intake at the cost of exacerbated gut distress.
However, research has shown an alternative option to help alleviate exercise-induced gut distress. This work supports the idea that gastric emptying of carbohydrate can be accelerated by increasing overall dietary intake of carbohydrate days before exercise. In one study, individuals who supplemented with 400g of glucose for 3 days improved their gastric emptying time by an average of 8.4 minutes (8). A different study demonstrated that supplementing with 440g for 4-7 days accelerated gastric emptying of glucose and fructose by an average of 24 and 36 minutes respectively (9). Therefore, by improving the gastric emptying of simple carbohydrates, these nutrients are able to be digested, absorbed and used as energy more rapidly, minimizing the chance of gut distress symptoms occurring.
Another culprit behind exercise-induced gut distress is intake that exceeds the stomach’s volume capacity. Fullness is in part related to how full the actual stomach is and exceeding the stomach’s volume capacity may elicit gut distress symptoms. If stomach capacity is significantly limited, athletes may once again be left weighing the options between rehydration and avoidance of gut distress symptoms.
A solution may be found in “training” their stomach to hold tolerate content. While currently there are no established protocols to increase tolerance to larger food volume, progressively increasing the volume of food through the course of several weeks can increase the stomach’s food volume tolerance (10). In theory, this would reduce perceived fullness while improving the stomach’s volume capacity consequently reducing gut distress symptoms; however, doing so should be done with guidance of a qualified professional to ensure safety in practice.
GI diseases are estimated to affect 11 percent of the population in the United States (2). Gut abnormalities often compromise the GI tract’s ability to digest and absorb nutrients. Having a medical provider diagnose and provide a treatment plan for a GI condition is essential in minimizing gut distress. However, gut distress may also be a consequence of exercise unrelated to any medical GI condition. Nutrient timing, composition and food volume are important considerations to account for when attempting to mitigate exercise-induced gut distress symptoms. Increasing overall carbohydrate intake days before exercise has demonstrated the ability to increase gastric emptying of carbohydrate which minimizes exercise-induced gut distress symptoms.
Additionally, although there are no established protocols, a gradual increase of food volume over the course of several weeks may increase the stomach’s food volume capacity. This would in theory reduce fullness which would consequently reduce gut distress symptoms. However, as mentioned, doing so should be done with guidance of a qualified professional. Minimizing gut-distress symptoms can optimize an athlete’s performance and recovery. This can be achieved by engaging in optimal fueling strategies and screening for GI conditions.
This article was written by Glenn Castro, RD, a Collegiate and Professional Sports Dietitians Association Registered Dietitian (RD). To learn more about sports nutrition and CPSDA, go to www.sportsrd.org.
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- Storhaug C. L., Fosse S. K., Fadnes L. T. (2017). Country, regional and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. The Lancet, 2(10), 738-746.
- Gujral N., Freeman H. J., Thomson A. B. (2012). Celiac disease: prevalence, diagnosis, pathogenesis and treatment. World J Gastroenterol, 18(42), 6036
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- Costa R. J. S., Miall A., Khoo A., Rauch C., Snipe R., Camoes-Costa V., Gibson P. (2017). Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Applied Physiology, Nutrition, and Metabolism, 42(5), 547-557.
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- Jeukendrup A. (2017). Training the Gut for Athletes. Sports Med, 47(Suppl 1):101-110.