In a groundbreaking study released on March 26, 2025, researchers have found that during a marathon, the human brain temporarily "eats itself" by utilizing its own protective fat layer as an energy source. This revelation sheds light on the extreme demands placed on both the body and brain during long-distance running.
The study, published in the journal Nature Metabolism, involved ten marathon runners whose brains were examined using MRI scans taken before the race, immediately after finishing, and again two weeks and two months later. The findings revealed a significant decrease in myeline, the fat-rich protective layer surrounding nerve cells, particularly in areas crucial for motor coordination, sensory perception, and emotional processing.
Notably, the research indicated that in some brain regions, the reduction in myeline reached as high as 28 percent immediately following the marathon. However, the good news is that these levels returned to normal after two months, suggesting that the brain can recover from this temporary depletion.
Chantal van den Berg, a neurologist involved in the study, emphasized that myeline serves as a sort of emergency fuel during extreme physical exertion. "You can think of it as an insulating layer around a heating pipe," she explained to RTL Nieuws. "When other energy supplies are depleted, the brain can switch to burning myeline, which consists of nearly 80 percent fats." This process, while alarming at first glance, is a testament to the brain's adaptability under stress.
Previous animal studies hinted at myeline being used as an energy source, but this is the first time evidence has been found in humans, marking a significant step in understanding the brain's response to prolonged physical challenges. Despite the intriguing findings, researchers caution that the study's relatively small sample size necessitates further investigation to draw definitive conclusions about the effects of myeline depletion on cognitive functions such as movement, thought, and emotions.
Van den Berg acknowledged the potential implications of this research, suggesting that temporary decreases in myeline could affect motor skills, coordination, and sensory capabilities. However, she reassured avid runners and fitness enthusiasts that there is no need for alarm. "This phenomenon primarily occurs with extreme distances. For regular exercise, there is little to no decrease in myeline," she said.
For those who enjoy running but may not be training for marathons, the study's findings are particularly reassuring. The myeline levels in the participants rebounded after a few weeks, indicating that the brain can recover quickly from the stress of long-distance running. Van den Berg also recommended a diet rich in healthy fats, such as fatty fish, nuts, and avocados, which can support brain health and myeline production. She also advised runners to ensure adequate rest after completing a marathon to help facilitate recovery.
As the research community continues to explore the intricacies of the brain's functioning during extreme physical activities, this study opens up new avenues for understanding the relationship between physical exertion and cognitive health. While marathon running is not for everyone, the implications of this research could resonate with athletes and fitness enthusiasts alike, encouraging them to consider not just the physical but also the neurological demands of their sport.
The study's authors acknowledge that while the findings are significant, they are just the beginning. More extensive studies are needed to fully understand how temporary myeline depletion might influence long-term brain function and whether it has any lasting effects on those who regularly engage in extreme endurance activities.
In summary, the revelation that the brain can temporarily use its protective fat layer as fuel during marathons is both fascinating and concerning. It highlights the incredible resilience of the human body, particularly the brain, during strenuous physical challenges. As runners lace up their shoes for the next race, they can take comfort in the knowledge that their brains are capable of remarkable adaptations, ensuring they can continue to push their limits.
