Dr. Douglas W. Stoddard

“The Road to Kona-Supplement to Inside Triathlon”

Many of you have experienced the nausea, cramping, bloating and pain that can accompany stomach and intestinal distress. These symptoms are directly related to your gastrointestinal (GI) system malfunctioning; therefore, I will call these “primary” symptoms.

The symptoms that you may not attribute to GI dysfunction but that can be related are bonking (low blood sugar), muscle cramping, muscle burning and dizziness. These symptoms I will call “secondary” GI symptoms. Secondary symptoms can be indirectly related to GI dysfunction through malabsorption – where your stomach and intestines are not adequately absorbing the fluid and nutrients required to sustain performance. Therefore, your stomach/intestines play a huge role in optimizing (or not) your training and competing.

Several causes for digestive system dysfunction exist.

Blood Flow

“Blood flow” problems stem from the fact that the stomach and intestines (and other digestive organs like the pancreas, gall bladder and liver) require a certain amount of blood flow to function optimally. During exercise, blood flow is shunted away from your digestive system in order to supply your muscles with oxygen/energy, to remove waste products of metabolism from your muscles and to supply your skin with blood to aid in cooling/sweating.

The human gastrointestinal tract is not generally forced to digest and absorb fluid and nutrients with so little blood flow, which is a big reason athletes working hard run into trouble. Bear in mind that the more intense you are working (the higher your percentage of VO2 max), the more problematic these symptoms can become. The length of the event is also important (longer equals higher chance of symptoms). Finally, for those of you who bike, the mechanical compression exerted on your abdominal region resulting from riding in the aero position may also play a role in impairing blood flow to your GI system.

Prevention of blood flow-related GI dysfunction means you must train your GI system to work with less blood. This means during training, drink and eat as if you were in a race. Secondly, you may have to slow down during a race, reducing the blood required in your muscles and skin and allowing more blood to flow to your GI system. This can help reverse what may seem like a very uncooperative digestive system. Finally, I advise anyone on a bike to sit up out of the aero position for 30-60 seconds at least once every 15-20 minutes, especially if you are GI sensitive.


Inside Triathlon anxiety and nervousness have an incredible effect on the digestive system. Nervous impulses can alter the way your stomach and intestines work, often leading to the primary symptoms of nausea, cramping, bloating, pain and diarrhea. Also, various hormones secreted in response to exercise and anxiety, such as adrenaline, can have a negative effect on the GI system. Most athletes Inside Triathlon have had at least one episode of diarrhea prior to an important event, which is attributable to these nervous/hormonal factors.

Prevention of anxiety-related GI dysfunction is challenging at best. Anxiety explains the common complaint – “everything seemed fine in training, but my stomach just shut down during the real thing.” Assuming that your nutritional plan did not change from that which you followed in training, anxiety may well have been the culprit. Never underestimate the power of anxiety and its role in shutting down your digestive system when the stakes appear to be high. Sport psychologists can help teach you to harness all of that nervous energy and use it to your advantage.

Carbohydrate source and concetration

Your choice and concentration of carbs can play a dramatic role in the functioning of your gut. Fructose, or fruit sugar, is a sweet sugar found in many sports nutritional products. It also happens to be a well-known irritant to the stomach and intestine. Gut-troubled athletes should not ingest this sugar during training or competition. Natural sources of fructose include bananas and other fruits – these should also be avoided. More GI friendly carbs include dextrose, sucrose, maltodextrin and amylopectin starches.

Concentration of carbs ingested is also important. All gels have a high concentration of carbs in them, and highly concentrated carbohydrate substances like these can be irritating to the GI system. This is a tough issue for which there is no easy remedy, as in order to ‘get the calories in’ Inside Triathlon, one has push the limits of their GI systems. However, one factor is the concept of resistant starch, which is derived from amylose, a common vegetable starch often used to make maltodextrin and other carbohydrate chains used in sport nutrition products.

If your sport nutrition products contain maltodextrin, as many do, ask the manufacturer what carbohydrate sources were used to manufacture the maltodextrin. Since cornstarch is the most abundant source for these carbohydrates, it’s important to know that there is only one variety of corn grown that has no amylose, and that is ‘waxy maize’ corn. The most common variety of corn, called Dent corn, contains about 30-40% amylose, as does the less common variety of ‘amylomaize’ corn, which is for all intents and purposes pure amylose. Resistant starch escapes digestion, and passes through to the colon, behaving like fibre, and potentially contributing to gas, bloating, cramps, nausea and diarrhea.

Also, your sports drink should have no more than a six-percent solution of carbohydrate in it (some have up to eight percent). Basically, this means a maximum of 60 grams carbohydrate per liter. Inside Triathlon Higher percentages of carbohydrates in your drinks may slow down digestion, and this is compounded when using highly concentrated carbohydrate sources like gels.

Too much “stuff” in your nutrition plan

The more “stuff” packed into your competition diet, the more potential for irritation. This is due to a concept called osmolarity, and its close cousin, osmolality. Both of these concepts involve the number of particles (atoms and/or molecules) dissolved in a solution. The more particles in a solution, the higher the osmolarity or osmolality – and the more potentially irritating it is to the gut.

Some companies are trying to make their drinks the answer to everyone’s nutritional needs, including everything from protein to chromium. A sports drink used during training and competition should be as “clean” as possible, supplying only the Big 3, those being carbohydrate, electrolyte and water. Adding more than this means more potential for gut irritation.

Sure, you need protein and trace minerals like chromium as well as a whole host of other things for optimal health. However, the time to ingest these is not during training and competition, especially if you are GI sensitive. Your daily diet needs to supply all of this other stuff.

The “empty stomach” syndrome

This syndrome results from not having at least a partially filled stomach at all times during your training/competition. Gastric (stomach) emptying decreases exponentially as gastric volume decreases. Therefore, you must maintain your gastric volume, i.e. always have something in your stomach. Again, this underscores the importance of training with food and fluids. Start your race with something in your stomach, and make sure you keep it “topped off” with fluid and food throughout.

Lactic acid buildup

It is well established Inside Triathlon that gastric emptying is reduced with rising lactic acid levels. Lactic acid is a product of glycolytic anaerobic metabolism (glucose metabolism without oxygen), and more is produced as your exertion level rises closer to VO2 max. This must be controlled, and ingesting substances that buffer lactic acid can be helpful, citrate being the most FI friendly.

Also, stemming the production of lactic acid is important if you are struggling, and this ties into the concept of reducing your exertional level, or slowing down. This means less reliance on the glycolytic anaerobic system and less production of lactic acid. Thus, lowering your exercise intensity can help not only by allowing more blood flow to your GI system, but also by reducing lactic acid production.

Ingesting caffeine

Ingesting caffeine-containing substances may contribute to your GI problems as caffeine helps induce relaxation of your gastroesophageal sphincter (the valve between your esophagus and stomach), which can contribute to heartburn and stomach pain. Many sports nutrition products contain caffeine, presumably for its stimulatory effect and effect on free fatty acid metabolism (it should also be noted that caffeine may also have an inhibitory effect on carbohydrate metabolism – probably not good for endurance athletes). Again, if you are stomach-sensitive, you might want to avoid caffeine both in your daily diet and during training and competition.

Dehydration, electrolyte depletion and bonking

Failure to maintain adequate hydration, electrolyte and blood sugar levels all can contribute to GI shutdown, which can lead to dehydration, electrolyte depletion and hypoglycemia. Thus, a vicious cycle develops, and this has ruined athletic events for many individuals. The gastrointestinal tract is highly dependent on normal hydration, electrolyte (especially sodium and potassium) and glucose levels for optimal function.

Falling hydration, electrolyte and glucose levels only increase the risk of GI shutdown. Once in this state, it is difficult, if not impossible, to digest and absorb necessary fluid and nutrients to fuel your performance – bloating, nausea, flatulence and diarrhea usually result. Ask yourself: “Am I replacing what I am losing?” Bear in mind that your sweat has an average of 700-1200 mg of sodium per liter and 180-315 mg of potassium per liter.


This is a measure of acidity Inside Triathlon. Stress, whatever the source, induces elevations in the acidity of your stomach. Exercise counts as stress, especially if particulary intense or long. Ingesting highly acidic foods and fluids never helps this issue. Check out pH comparisons in the product comparison charts on this site.

Medical causes of gut shutdown

While the above causes may be applicable to you, you may have other medical reasons for your GI problems. Seeing a sports medicine doctor is a good place to start. Various conditions like reflux esophagitis, ulcers, gastritis, dysmotility and gallstones can all cause gut symptoms. All are treatable, once diagnosed. How do you know when to see your doctor? Simply, if you have any GI symptoms outside of exercising times, or, if you have tried addressing the above causes during exercise and you are still struggling.

Dr. Douglas W. Stoddard is the medical director of the Toronto Sports & Exercise Medical Institute, Iron man Canada and the Subaru Triathlon Series.

Dr. Douglas W. Stoddard
“The Road to Kona-Supplement to Inside Triathlon”