Power to the Poople

Sometimes It Really Pays to Give a Shit!

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Bernard Picart (1673-1733) The Perfumer

We’re all familiar with the fable recounting the gag argument among the various organs of the human body as to which is most valuable and should be in charge. Even though the brain, blood, stomach, liver and so on put forward compelling arguments as to why what they do should be seen as most important, the rectum wins after not doing its job for several days and distressing every other body system. The moral of the fable is simple: while others do most of the work, the asshole is always in charge. Now, two recent multi-institution studies published in 2023 and 2025, and led by Dr. Chen-Chan Wei of the University of Taipei Laboratory of Exercise Biochemistry, suggest that there is, in fact, some truth to this bit of scatological humor. These researchers looked at how rectal distension (constipation, or more to the point lack of defecation) impacts both physical (2023) and cognitive (2025) performance in elite athletes. So, shall we have a go at what they found out, and how it relates to not only what is evolution’s ‘first brain’ but also traditional Asian spirituality?

Both studies derive from the same clinical trial involving 13 triathlete college students, 7 males and 6 females, with a mean age 20.3 ± 0.5 years. The objective in both studies was to examine how defecation versus non-defecation affected blood distribution and oxygenation between the central nervous system (CNS), specifically the prefrontal cortex, and the sub-navel enteric nervous system (the ‘gut’). The argument here is that defecation reduces competition for oxygenated blood serving the CNS (the ‘brain’) versus the ENS (the ‘gut’) [see footnote 1].

The 2023 Study

The premise of this study was that exercise increases metabolic O₂ demand, to be met by increasing blood flow to the prefrontal cortex, as one of the functions of this part of the brain is coordinated voluntary muscle movements (contractions). If constipation does in fact create competition for blood between the ENS and CNS, then pooping should in theory remove that competition thus providing the prefrontal brain with the extra blood supply needed to support increased exercise and enhance performance.

The elite athletes were tasked with performing an endurance cycling time trial in both a defecated and non-defecated condition. Each athlete cycled to a point of 80% VO₂ Max, a standard measure of aerobic fitness and the efficiency with which the body can deliver oxygen to muscles during exercise. There was a one week ‘wash-out’ period between the two trials with monitoring and control of potential ‘confounding’ conditions such as diet, sleep, use of supplements, stimulants and alcohol (the last three to be avoided) and self-reported ‘habitual bowel evacuation’ times for each participant. (Of the 13 participants, 11 were morning poopers, and of these 11, 7 reported ‘going’ at or around 9:00 am.) For this study, the researchers measured the status of blood flow in the body (aka hemodynamic variables), including blood pressure, tissue oxygenation and blood distribution. These measures were recorded at both the sub-navel level (ENS) and at the prefrontal cortex (CNS). Also measured was cycling time to exhaustion (i.e., how long did it take to reach VO₂ max).

What they found was that defecation led to greater blood perfusion at the prefrontal cortex and improved endurance for the exercise regimen. In other words, more blood was reaching the CNS and muscle fatigue was delayed because of pooping. While not significantly different between the two situations, blood pressure was lower for the defecation group, which was expected as previous research has documented a relationship between rectal distension and hypertension, and has shown that other regions of the brain are activated in addition to the prefrontal cortex, notably the cingulate cortex, inferior parietal lobule, and putamen. Interestingly – and unexpectedly = they also found that oxygen consumption was increased at the sub-navel location in the defecated condition. What the actual physiological role is for this outcome remains unknown, but the authors note that it suggests that the ENS is also implicated in “sustaining muscle contraction in humans”.

The bottom line (sorry!) from this study is that if you like to work out, it is best to go to the bathroom before you go to the gym!

The 2025 Study

The Chen-Chan Wei lab then published a follow-up study looking at the impact of defecation on cognition, under the premise that constipation has been shown to lead to “poor frontal executive performance in patients with dementia [suggesting] a possible communication between the rectum and the brain”. Their justification for conducting this trial with elite athletes was that triathlons involve split second decision making, weighing various options to overcome challenging and unforeseen situations in besting competitors – tasks relegated to the prefrontal cortex. However, for this leg of the clinical trial the researchers added an additional variable, comparing the non-defecated state with both natural defecation as well as induced defecation. This was achieved through dietary supplementation of magnesium oxide, well known for its role in relieving constipation [see footnote 2]. Induced pooping has two benefits from the study’s perspective: it reduces stress on the rectum, and it would also likely reduce variation in the athletes’ schedule’ for bowel evacuation.

The same protocols were used to measure hemodynamic variables (blood oxygenation, distribution etc.) as in 2023, and at the same locations (CNS and ENS). Note that a reduction in blood oxygenation at a given site with no change in distribution overall translates into increased oxygen consumption at that location.

Cognitive performance was evaluated using the Stoop Color-Word Test (you can look it up – I had to!). This test challenges participants to complete 5 tasks involving color- and word matches and mismatches. The first task established a baseline: each triathlete read aloud 50 words stating a color (blue, green or red) printed in black ink. The remaining tasks fell into either a ‘congruent phase’ (the color words were printed in their correct color, or placed in a correctly colored box – e.g.., the word ‘red’ was printed in red ink) or an ‘incongruent phase’ (the words may or may not have been printed in their correct – matching – color OR the word for the color never matched the actual color (the word ‘blue’ might have printed in red ink - like I said, you can look it up!). The subjects were asked to correct any errors before moving on to the next task and the time to complete all tasks was recorded in seconds. The more errors made at each task, the longer it would take to complete the entire 5-stages of the Stroop Color-Word Test, providing a measure of a decrease in cognitive performance. Whew!

It turned out that the poorest performance was recorded for the non-defecated condition (27.1 ± 1.1 seconds), and the best by the induced defecators (23.4 ± 0.8 seconds), a statistically significant difference. The habitual defecators were a little slower, at 24.4 ± 0.9 seconds. At the individual level induced defecation improved performance in all 13 athletes, and non-induced defecation in 9/13 athletes. They also found that, at the sub-navel location, blood oxygenation decreased with no change in distribution, indicating an increase in oxygen consumption at the ENS. This result was not found at the CNS (prefrontal cortex).

OK, so what is going on here? Fact is, we don’t really know. What we do know is that the ENS – which communicates with the CNS primarily via the vagus nerve – has a high density of neurons (over 100 million), including efferent and afferent neurons, as well as interneurons [see footnote 3] making it able to function independently of input from the CNS in regulating functions of the gastrointestinal tract. This makes sense if we consider that, evolutionarily speaking, digestion and waste processing would have been essential processes prior to the appearance of the ‘head brain’. Recall that the ENS is considered the ‘first’ brain from the perspective of evolution (though neuroscientists call it the ‘second brain’ in terms of cognition). The study’s authors speculate that, with defecation, basal activity’ is reduced for nerves in the rectal region (i.e., rectal distension is no longer attention) which, in turn, reduces load in the CNS. This ‘frees up’ neural energy, as it were, for cognitive function.

Here’s another thought: as shown by these two studies, if defecation improves both cognitive function and athletic accomplishment in athletes, should supplements such as magnesium oxide be considered performance enhancing ‘drugs’ by the World Anti-Doping Agency? Hmmmmm….

And finally, what does all of this have to do with Asian spirituality? Here we loop back to the finding reported in both studies of increased O₂ consumption in the sub-navel region. In Chinese tradition medicine, the life force known as qi exists in the three Dantians, found in the head, the chest (heart) and the lower abdomen – the latter Dantian corresponding to the sub-navel region examined in these two studies. Similarly, we can look to possible connections in Japanese (Hara) and Indian (Sacral Chakra) spirituality. So, the next time you have that ‘gut’ feeling about something, you might want to pay attention to it!

Footnote 1. From an evolutionary perspective the enteric nervous system is considered the primal, or first, brain, found not only in chordates (i.e., animals like us] but also in animals that do not have a central nervous system such as hydra and sea cucumbers. There are, however, very complex neuronal connections between the ENS and the CNS.

Footnote 2. Magnesium oxide is one of several forms of magnesium that can be taken for constipation. It is a salt and thus works by osmotically drawing water into the intestines. This additional water is absorbed by the stool which both softens it as well as increases its volume. This then turns on stretch receptors in the colon, triggering a cascade of muscle contractions (peristalsis) that moves the stool toward the rectum. Magnesium oxide typically works within 6–12 hours.

Footnote 3. Efferent neurons are also known as motor neurons, and afferent neurons are also known as sensory neurons. Thus, sensory neurons inform us as to what we are experiencing (sensations), while motor neurons allow us to respond to it (i.e., by some form of movement). As you might guess, interneurons connect afferent and efferent neurons.

Where to find the Science:

Chen-Chan Wei, M. Brennan Harris, Mengxin Ye, Andrew Nicholls, Ahmad Alkhatib, Luthfia Dewi, Chih-Yang Huang, and Chia-Hua Kuo (2025) Defecation after magnesium supplementation enhances cognitive performance in triathletes. Sports Medicine and Health Science 7: 102-108. https://dx.doi.org/10.1016/j.smhs.2024.04.001 

Chen-Chan Wei, Giancarlo Condello, Ai-Lun Yang, Szu-Hsien Yu, Yi-Hung Liao, Chung-Yu Chen, Chi-Chieh Hsu, Chi-Yang Huang & Chia-Hua Kuo (2023) Defecation enhances cerebral perfusion and delays fatigue in elite triathletes, Journal of the International Society of Sports Nutrition, 20:1 https://dx.doi.org/10.1080/15502783.2023.2206380