DATE: March 20, 2025 at 06:00AM
SOURCE: PSYPOST.ORG

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TITLE: Defecation and cognitive function: A surprising link discovered in elite triathletes

URL: psypost.org/defecation-and-cog…

A new study published in Sports Medicine and Health Science suggests that defecation may improve cognitive performance in elite athletes. Researchers found that participants completed a demanding cognitive task, the Stroop test, more quickly after defecation than when they had not defecated. Magnesium supplementation, which aids bowel movements, further enhanced performance.

The motivation for this study arose from an unexpected observation in a previous experiment. While conducting a PET scan to measure glucose metabolism across the body, researchers noticed that a region near the rectum displayed glucose uptake levels comparable to those in the brain.

They suspected the signal was an artifact caused by glucose accumulation in the bladder. However, three-dimensional PET imaging confirmed that this highly active area was distinct from the digestive tract. Given that glucose is the primary energy source for neural activity, the discovery raised an intriguing possibility: Could this region play a role in cognitive function?

This question gained further support from clinical observations. Studies have linked constipation to impaired executive function in dementia patients, suggesting that rectal health might influence cognitive performance. Additionally, historical theories propose that the enteric nervous system—a network of neurons embedded in the gut—could function as a “first brain” that evolved before the central nervous system.

“Many years ago, we conducted a PET scan to measure relative glucose uptake across the human body. Unexpectedly, we observed that the subnavel region exhibited glucose uptake similar to that of the brain (highest in the body),” explained study author Chia-Hua Kuo, a professor at the University of Taipei. “To investigate further, we hypothesized that manipulating pressure in this region might influence cognitive processes, particularly judgment-based decision-making tasks and exercise performance.”

Thirteen elite college-aged triathletes participated in a randomized crossover trial with three conditions: non-defecation, voluntary defecation without supplementation, and defecation after magnesium intake. The study design included a one-week washout period between each condition to prevent residual effects. Participants followed a controlled diet and fasted overnight before each session to minimize dietary influence. Testing was conducted in the morning, with all participants urinating upon waking and consuming a fixed amount of water before defecation.

To assess cognitive function, the researchers used the Stroop test, a widely recognized measure of executive function. This test requires participants to quickly identify the color of printed words, even when the word itself represents a different color (e.g., the word “red” printed in blue ink). The test challenges selective attention and cognitive flexibility, with faster completion times indicating better performance.

To examine physiological changes, the researchers measured blood distribution and oxygenation levels using near-infrared spectroscopy (NIRS). Sensors were placed on both the prefrontal brain, a region associated with executive function, and the sub-navel region, where the highest glucose uptake had been observed in previous PET scans. By comparing changes in blood flow and oxygen consumption during the Stroop test, the researchers aimed to determine whether defecation influenced cognitive function through physiological mechanisms.

The researchers found evidence that defecation improved cognitive performance. Participants completed the Stroop test more quickly after defecating compared to when they had not. On average, completion times were 27.1 seconds in the non-defecation condition, 24.4 seconds after voluntary defecation, and 23.4 seconds after magnesium-induced defecation. Every participant performed better after magnesium supplementation, and the majority (69%) performed better after non-supplemented defecation. This suggests that rectal emptying alone contributes to improved cognitive performance, with magnesium potentially enhancing the effect.

“Our findings suggest that the rectal region plays an unexpected role in rapid decision-making,” Kuo told PsyPost. “Reducing pressure in this area may enhance cognitive judgment, potentially offering practical applications for mental performance.”

Physiological measurements provided further insights. Despite no significant changes in blood distribution to the prefrontal brain, oxygen levels in the sub-navel region decreased after defecation, indicating increased oxygen consumption in this area during the cognitive task. This pattern suggests that this lower abdominal region may play an active role in rapid cognitive processing.

“We found that defecation increases oxygen consumption in the subnavel region during judgment tasks, indicating a possible link between gastrointestinal activity and cognitive function,” Kuo said.

The results challenge traditional assumptions about cognition being solely centered in the brain. The gut’s enteric nervous system, often called the “second brain,” contains extensive neural networks that communicate with the central nervous system. The findings of this study imply that rectal activity might influence cognitive efficiency, potentially explaining why sensations in this region—often described as “gut feelings”—are linked to instinctual decision-making.

But there are limitations to consider. The sample size was relatively small, consisting only of 13 elite triathletes. Future research should examine whether similar effects occur in different populations, including non-athletes, older adults, and individuals with gastrointestinal disorders.

Additionally, the study did not explore the long-term effects of magnesium supplementation or whether regular bowel habits influence sustained cognitive performance. Further research is needed to determine whether other factors, such as microbiota composition or gut motility, contribute to the observed effects.

The findings also raise questions about the broader role of the enteric nervous system in cognition. The high glucose uptake and increased oxygen consumption in the sub-navel region suggest that this area may serve a previously unrecognized function in rapid decision-making. Future studies using neuroimaging techniques could investigate whether neural activity in this region correlates with specific cognitive processes.

The researchers are now investigating alternative methods of inducing defecation to further understand the relationship between rectal activity and cognitive function. “We are currently exploring the effects of glycerin-induced defecation to further investigate this phenomenon,” Kuo said.

The study, “Defecation after magnesium supplementation enhances cognitive performance in triathletes,” was authored by Chen-Chan Wei, M. Brennan Harris, Mengxin Ye, Andrew Nicholls, Ahmad Alkhatib, Luthfia Dewi, Chih-Yang Huang, and Chia-Hua Kuo.

URL: psypost.org/defecation-and-cog…

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