When a runner complains of a troublesome gut, a well-meaning coach or dietitian will often quickly search for answers by looking at the standard perpetrators: poor food choices, underhydration, ingestion of gut-provoking medications, inadequate training. In other cases, it turns out that a runner’s gut distress arises because of a more serious issue like Celiac disease or inflammatory bowel disease.
Oftentimes, though, the origins of gut woes can be maddeningly hard to pin down. In some respects, medical conditions like irritable bowel syndrome (IBS) and dyspepsia fall into this enigmatic diagnostic category, in that there is usually no obvious anatomical defect to the digestive tract. As such, these conditions are often labelled as functional gut disorders because it is the function, not the structure, of the gut that seems most affected.
Although much is still to be learned about IBS, dyspepsia, and other functional gut disorders, there is at least one important shared feature to the pathology of these diseases: visceral hypersensitivity. In basic terms, hypersensitivity means a person experiences discomfort/pain in response to a typically non-painful stimulus, or that they report heightened pain from something that causes most people mild discomfort. More specifically, visceral hypersensitivity refers to these sorts of pains/discomforts in the body’s abdominal region.
Importantly, a person can exacerbate or lessen visceral hypersensitivity based on the lifestyle choices they make. For runners, this has potentially important implications for preventing and managing some types of gut distress during training and competition. In this article, we’ll take a close look at some of these lifestyle choices and how they just might lesson a runner’s odds of being stricken by gut troubles.
Visceral Hypersensitivity and Functional Gut Disorders
If you’re not familiar with IBS, it’s a disorder that predominantly impacts that lower half of the digestive tract, with common symptoms being the backdoor trots, straining on the loo, abdominal cramping, and bloating. Many studies have found that people with IBS are often viscerally hypersensitive. To figure this out, researchers conduct fun-sounding procedures (insert sarcasm) like rectal barostat testing. Lucky volunteers start by undergoing a bowel cleansing protocol, which is followed by the insertion of a balloon into the rectum. Said balloon is then gradually inflated until the volunteer can’t take the pressure any longer. In one illustrative study, people with IBS handled only about half as much balloon pressure as healthy subjects. In another study, the severity of IBS symptoms was correlated with pain thresholds from barostat testing. All in all, these and other experiments strongly support the idea that visceral hypersensitivity is an important contributor to IBS.
Dyspepsia is an exceedingly common gut disorder, with estimates of about 10–40 percent of people in Western countries being afflicted. In Greek, the prefix dys- means bad and peptos translates loosely to digestion; hence, the phrase dyspepsia has historically been used to describe many a condition marked by indigestion or an upset stomach. In contrast to IBS, dyspepsia’s symptoms generally originate from the upper gut and include excessive or premature fullness, upper abdominal discomfort, and heartburn. Although dyspepsia can be due to readily identifiable causes like ulcers, in many instances there is no structural defect to the gut, and the term functional dyspepsia is used to describe these cases.
Like with IBS, visceral hypersensitivity has been documented in studies of dyspeptic patients. Take for example an experiment that administered capsaicin to volunteers with functional dyspepsia as well as healthy folks. Capsaicin is a major constituent of chili peppers and gives them their spicy kick. The study volunteers ingested 0.5-gram capsules of capsaicin every 15 minutes until they reported moderate pain. In the end, two-thirds of the dyspepsia patients reported moderate pain after just one capsule, while only half of the healthy people did. Interestingly, about 10 percent of the healthy volunteers were able to handle four or more capsules while none of the people with dyspepsia could.
Because visceral hypersensitivity plays an important role in both IBS and functional dyspepsia, it is perhaps not overly surprising that many people with one of these disorders also has the other. In one analysis of outpatients from a gastroenterology clinic who had been diagnosed with at least one of these ailments, 64 percent of them met the criteria for having both disorders based on a standardized questionnaire.
Nervous System Dysregulation
Sensations that you perceive in your gut and visceral region of your body are controlled by your nervous system. Sensory nerves in and around your gut detect chemical and mechanical stimuli, and this information is ultimately relayed to your spinal cord and brain. This means that aberrations anywhere along this chain can make your gut hypersensitive, and it has been speculated that visceral hypersensitivity is due to a combination of the following: 1) sensitization of sensory nerve endings in the gut wall, 2) greater flow of sensory information through nerves of the spinal cord, and 3) amplification of sensory information in the brain. Regardless of what the true mechanisms are, we know a person’s visceral sensitivity level can, to a degree, change over time based on their environment and lifestyle choices.
One of the most consistent things that induces visceral hypersensitivity is acute stress. In patients with IBS, for instance, placing a hand and forearm into a tub of ice-cold water amplifies pain sensitivity to electrical current in the rectum. (These hypersensitivity experiments sound like a treat, huh?) Dipping your hand in bitterly cold water is a sort of mixed physical-psychological stressor, so perhaps you’re wondering if a similar response would be seen with a purer psychological stressor. It turns out that simply listening to one type of music (folk) in one ear while simultaneously listening to another type of music (rock) in the other ear can also increase rectal pain sensitivity in people who have IBS.
Beyond acute physical and psychological stress, what else can aggravate visceral hypersensitivity in people with IBS, dyspepsia, or other gut disorders? There are many possibilities, but sleep loss and dietary factors are at the top of the list. Individuals with acid-reflux disease were found in one experiment to have more pain with acid exposure after one night of getting less than three hours of sleep, which jibes with other research showing that sleep deprivation makes general pain perceptions worse. On the dietary side of things, it’s well documented that among patients with IBS, lowering the intake of what are called FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) is often associated with symptom improvement. FODMAPs are short-chain carbohydrates that aren’t digested and absorbed particularly well in some folks. Recent experiments have even pointed to less visceral hypersensitivity as a possible explanation for symptom improvements with low-FODMAP diets (see here and here).
Targeting the Nervous System and Mind to Reduce Visceral Hypersensitivity
Clearly, visceral hypersensitivity is more likely to be a problem for runners who suffer from IBS, dyspepsia, regular reflux, and the like. Still, there is reason to suspect that many people, even those who don’t have one of these illnesses, are susceptible to becoming a bit more hypersensitive to pains and discomforts in certain situations.
Race morning is a prime example of when visceral hypersensitivity could rear its ugly head. This may be precisely why some runners are unable to consume their regularly sized pre-exercise meal; they are so stressed and nervous that their gut has become oversensitive to even the smallest food portions. Obviously, this could have implications for being able to carry out pre-race and in-race nutrition plans.
What, then, are some strategies runners can implement to decrease visceral hypersensitivity or the chances they will encounter this problem in the future? Obviously, avoiding undue psychological stress and sleep deprivation are important pieces of the puzzle, but in both life and sport, there are many situations that are unavoidably stressful. In these circumstances, one simple intervention that may diminish visceral hypersensitivity is slow deep breathing (e.g., six breaths per minute), which may stem from its capacity to activate the parasympathetic (“rest and digest”) branch of your nervous system. To ensure that you are fully activating the parasympathetic branch of your nervous system, it’s important to exhale fully and slowly (i.e., over 4 to 5 seconds) with each breath cycle. Even a few minutes of slow deep breathing is enough to get the parasympathetic nervous system going, though doing it for longer may elicit greater effects.
A way to get potentially even more benefits out of slow deep breathing is to add in a mindfulness component. The practice of being mindful basically means trying to focus on the present moment instead of the past or future. Constantly ruminating on the past or excessively worrying about the future often leads to mental and physical problems, so there is a strong rationale underpinning the practice of mindfulness. Your focus of attention when doing mindfulness training can be on bodily sensations, thoughts, feelings, or things in your environment. A key aspect of most mindfulness techniques is to avoid judgment when your mind eventually wanders. One of the simplest ways to be more mindful is to count your breaths, which can easily be paired with slow deep breathing. The evidence behind mindfulness meditation as a pain reducer is somewhat mixed and the research quality has not always been great, but the chance of any harm from trying it is low.
Diet and Medication Fixes
For people with IBS, following a low-FODMAP diet may bring some relief, though the long-term health effects of eating this way are largely unknown. An alternative to a long-term low-FODMAP diet is to just avoid them for the day or two before an important training session or race. From a practical point of view, low-FODMAP diets can be a bit complicated to follow, in large part because FODMAPs are found in most food groups and there is not a simple rule of thumb when it comes to the types of foods that should be avoided. (Information on what foods contain FODMAPs can be found here.) In addition, people have different thresholds in terms of the amount of FODMAPs they can ingest before they start to experience gut problems. If you can afford it, consulting with an experienced dietitian or nutritionist would be ideal when implementing a FODMAP-restricted regimen.
Finally, athletes who have been diagnosed with IBS or functional dyspepsia could potentially benefit from certain drugs, such as antidepressants, that have reduced visceral hypersensitivity in some studies, and interested individuals should talk to their doctor. If you haven’t been formally diagnosed with IBS but suspect you could be suffering from it, you could take the following screening survey.