Running – gastrointestinal problems, and what to do about them
by Stacy Sims
I recently gave a talk to a room full of runners, some experienced marathoners, others just starting to get into the race scene with a couple of 5 or 10km runs.
The one thing that they all had in common, GI issues. Regardless of planning or what they’ve heard (celery the night before?!!!), they still couldn’t get over the fear and real occurrence of gastrointestinal disturbances.
Let’s have a closer look. Different types of upper and lower GI symptoms occur in ~45-50% of runners. The symptoms may be related to more than one causal factor. The physiology is complex, so the fuel (carbohydrate choices primarily) and fluid you put into your system may compound the problem(s).
The Physiology: When exercise is intense or when dehydration causes hypovolemia (decreased blood volume), exercise induces changes in blood flow by the virtue of shunting blood from the gut to the working muscles. This blood shunt effectively causes a bit of hypoxia to the GI tract and increases neural activity of the submucosa of the gut (the connective tissue). This change to the GI tract increases the secretion of certain hormones and decreases absorption through the intestinal cells. This combination induces diarrhea, intestinal cramping, delayed gastric emptying (extra pressure in the stomach-“slosh” factor), and some bleeding of the stomach and colon may result (which is why some individuals experience blood in the urine and stool). The common use of anti-inflammatory drugs (NSAIDs, aspirin) aggravate the bleeding and interferes with fluid balance at the level of the kidneys (perpetuating the dehydration issue).
Exercise, in particular running (with its impact forces), promotes a reduction in the GI muscle tone and motility, leading to reflux from the stomach or loose stools escaping from the colon. None of this is pleasant, for sure.
Both upper and lower GI symptoms are affected by exercise intensity, recency of meals, specific food intake during exercise, and ingestion of acidic drinks (coffee, orange juice). Anxiety tends to induce lower GI symptoms and of additional interest, there tends to be a sex difference in symptoms as well. Women have a 5:1 increased risk of diarrhea, intestinal cramping, and side aches as compared to men; men tend to have greater risks of vomiting and nausea. Most of this increased lower GI symptom risk is attributed to the fluctuation of estrogen and progesterone, with a greater incidence of lower GI issues during the 5-7 days preceding menstruation (aka the high hormone phase of the menstrual cycle).
So… What do I do?
The pre-race meal
Your food choices, timing of meals and hydration status can dramatically improve or worsen GI symptoms you experience during exercise.
One of the most common mistakes athletes make on race day is to gauge the size of their pre-race meal on the distance of the event. This faulty reasoning can lead to a host of GI problems as excess amounts of food will tax the body, demanding blood flow to the stomach while muscles in the periphery are screaming for fuel. If you know you have GI issues, it might be best practice to fuel up the day and night before, and topping up with a lighter pre-race/pre-exercise meal. This morning meal needs to have time to work it’s way through your system, so looking at a light breakfast that doesn’t have dairy (lactose intolerance), fructose (hard to digest and in general, few people cannot absorb more than 25 grams of fructose, even at rest, without experiencing some GI symptoms such as gas, bloating and possibly diarrhea), is low in fat and has moderate protein.
An example may include a high protein cereal such as Kashi GoLean with vanilla almond milk, and slice or two of low fiber bread (only pre exercise!!) with a bit of nutbutter and a sprinkle of salt. Best to avoid the breakfast smoothie; although delic, it is full of fiber, dairy, and protein (best to have this after your session!).
Best carbohydrate fuel during exercise
The goal in choosing the right food for a race day is primarily to provide fuel for the muscles without causing GI symptoms. As a rule, these types of food should have a blend of simple sugars to speed the delivery of the sugar from the stomach, through the intestinal wall, and into the blood stream. Be a label reader. With the competition stiff on the sports nutrition market shelves, more and more companies are moving towards “all natural” aka dried fruit, evaporated cane sugar and/or agave nectar. Cane sugar is fine, as it is sucrose. Products that contain fructose should be avoided as fructose is not rapidly absorbed through the GI tract, but has to go to the liver to be metabolized. A big amount of fructose in the intestines is associated with a reverse water flux- effectively dehydrating the body’s water stores and “flooding” the intestines, contributing to diarrhea.
What products should I avoid and which ones should I try?
Most gels are made of maltodextrin, fructose and most have additives like protein or fatty acids. The issue with gels is that they are a concentrated carbohydrate in a compromised gut (reduced blood flow), with the gel ingestion, there is a change in the osmotic pressure; means water has to come from within the system to “dilute” the carbohydrate for absorption. (see blog: maltodextrin and fructose)
What about blocs, chomps or jelly beans?
These products are generally not made of maltodextrin and fructose, so that solves one problem. Secondly, chewing small bits of carbohydrate ends up slowing the distribution of the load on the digestive system and allows for better absorption than swallowing a big bolus of gel.
What about sucralose and other sugar substitutes?
Increasingly common in sports drinks and engineered nutrition is the addition of sucralose, stevia, and/or sugar alcohols to maintain a sweet taste but reducing overall carbohydrate concentration.
The issue with these sugar substitutes is the effect on GI physiology as these compounds are not very well absorbed and can increase the osmotic load within the GI tract, become a source of energy to fuel rapid bacterial fermentation, and reduce gastrointestinal motility and alter bacterial flora.
One trick to try is to eat a few peppermint Tums (calcium carbonate) about 20 min before heading out the door. In an intensity session (e.g. track intervals, race), have some additional tums handy will help slow down any GI issues. The calcium works with neuromuscular contraction and muscle metabolism, the carbonate helps to “coat” the intestinal cells, reducing endotoxin release and the ensuing symptoms, and the peppermint is well used homeopathic remedy for GI disturbances.
To minimize GI issues, you should think about what you are eating the day/night before and try to minimize high fiber and high fat foods. Before heading out for your run, (be it a race, a track session, or a steady-state), if you are susceptible to GI issues, you’ll want to avoid dairy, high fiber, fructose, and high fat foods. Chew on a few peppermint tums and drink OSMO Active. During your run, pay attention to your nutrition and hydration plan- try a hydration strategy that doesn’t let fluid sit in your stomach, and try not to over eat (you can come back from low blood sugar, but it takes hours to come back from dehydration). And please, leave the anti-inflammatory drugs in the cabinet for real injuries!
Most of all, everyone is individual, so you’ll have to tweak your fluid and food intake to find your gold standard, but keep in mind the nuances described above, and your GI symptoms should quickly dissipate.