Unlocking the Mystery: How Intense Endurance Exercise Can Cause Your Brain to ‘Eat Itself’

When the brain runs low on energy, it might turn to its own fat for fuel. A recent study involving marathon runners shows some interesting findings about how our brains adapt during extreme physical activities.

Researchers scanned the brains of ten runners—eight men and two women—before and after they completed a marathon. The scans revealed that during the race, when glucose levels dropped, certain brain cells began to use myelin, the fatty coating that surrounds nerve fibers, as an energy source. This suggests a new way our brains can maintain function even when under stress.

Myelin is crucial for efficient nerve signaling, but it is not just a static insulator. New research indicates that neurons can adapt myelin thickness based on their environment. The study found changes in myelin markers in the brain’s white matter after the race, particularly in areas linked to motor skills and sensory processing. In the days following the marathon, the runners exhibited a substantial loss of myelin, but interestingly, those levels began to recover after two weeks and stabilized two months post-race.

Pedro Ramos-Cabrer and Alberto Cabrera-Zubizarreta, the leading researchers, propose that myelin acts like a metabolic safety net. It allows the brain to access a vital energy reserve when typical nutrients are low. This phenomenon, which they call "metabolic myelin plasticity," challenges the previous belief that the brain mainly relies on glucose as its primary energy source. Although the sample size of this pioneering study is small, it aligns with earlier studies on animals showing that myelin can serve as an energy reserve during nutrient shortages.

Interestingly, the brain’s reliance on myelin for fuel could explain why runners often experience slower reaction times and poorer memory performance immediately after running a marathon. This temporary cognitive decline seems to improve quickly with rest.

Historically, scientists viewed the brain as avoiding fat as an energy source, especially in stressful situations. However, new insights suggest a more complex interaction where myelin could be sacrificed in small amounts to maintain overall brain function. This delicate balance highlights an evolutionary adaptation crucial for human survival, allowing early humans to pursue prey while remaining alert and capable.

Understanding how the brain uses myelin during intense physical activity opens up new discussions about brain health and metabolism. It may also lead to better strategies for recovery in athletes and insights into neurological diseases like multiple sclerosis, where myelin is significantly affected.

This study is published in Nature Metabolism and adds a fascinating layer to our understanding of how our bodies and brains work together under stress.

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