Your Brain Might ‘Eat’ Its Own Myelin During Endurance Exercise

Your Brain Might Start 'Eating Itself' During Strenuous Endurance Exercise: A New Form of Neuroplasticity

When we push our bodies to the limits during intense endurance events like marathons, our muscles aren't the only things that are tested. New research suggests that our brain, too, undergoes a remarkable and surprising process of adaptation under extreme physical stress—one that may involve the brain "eating" its own myelin for fuel.

A pilot study led by neuroscientists in Spain has uncovered evidence that during strenuous endurance exercise, such as running a marathon, the brain may enter a state of emergency metabolism, where it begins to utilize myelin—the fatty sheath that insulates neurons—as a form of fuel when glucose, the brain’s usual energy source, runs low. While this finding may sound unsettling, it introduces a fascinating and potentially transformative concept: a new form of neuroplasticity that helps the brain maintain function even when energy resources are limited.

Myelin and Its Crucial Role in the Brain

Before diving into the details of this new discovery, it's important to understand myelin and its role in brain function. Myelin is a fatty substance that coats nerve fibers in the brain and spinal cord. Think of it as an insulating layer that allows electrical signals to travel efficiently between nerve cells. This helps speed up communication within the nervous system, enabling faster and more coordinated movements and thoughts.

For many years, scientists believed that myelin was simply a passive insulator, a static structure that didn’t change much over time. However, emerging research is challenging this view. It turns out that myelin is more dynamic than previously thought. Neurons can modify the thickness of their myelin in response to changing environmental demands. And, it appears that under extreme conditions, like prolonged endurance exercise, myelin may even serve as a metabolic reserve for the brain.

The Study: Marathon Runners and Brain Changes

In the pilot study conducted by Dr. Pedro Ramos-Cabrer and Dr. Alberto Cabrera-Zubizarreta, 10 marathon runners (8 men and 2 women) underwent brain scans before and after running a full 42-kilometer marathon. The goal of the study was to assess how the brain responds to the intense physical stress of long-distance running.

The results were striking. The brain scans revealed that 24 to 48 hours after the race, the runners showed a significant reduction in the markers of myelin within brain regions tied to motor function, coordination, sensory processing, and even emotional regulation. In other words, the brain appeared to have “lost” some of its myelin following the marathon. However, the damage wasn’t permanent. By the two-week mark, the myelin markers began to recover, and after two months, they had stabilized in the six participants who continued with the scans.

This change in myelin markers suggested that, during the race, the brain was utilizing myelin as a form of energy when its usual glucose stores ran low. Essentially, the brain may have been "recycling" its own fatty tissue to maintain function when the normal fuel sources were depleted.

Metabolic Myelin Plasticity: The Brain’s Safety Net

The researchers propose a novel concept to explain these findings: metabolic myelin plasticity. This term refers to the idea that myelin is not just a static insulator but also an energy reserve that the brain can tap into when other sources of fuel, like glucose, become scarce. In the case of marathon running, this could be a protective mechanism that helps the brain maintain functionality in a state of energy deprivation.

The concept of metabolic myelin plasticity challenges our previous understanding of the brain’s energy metabolism. While the brain has always been known to rely heavily on glucose for energy, this new study suggests that in extreme conditions, such as intense endurance exercise, it may also use fat stores in the form of myelin. This could be an adaptive strategy to preserve brain function when other energy sources are insufficient.

The Implications of the Findings

The results of this study are particularly significant because they suggest that the brain has the ability to adapt in ways that were previously unimagined. The ability to "borrow" energy from myelin during strenuous exercise could help explain why athletes sometimes experience temporary cognitive sluggishness—slower reaction times and diminished memory—immediately after a race. It's likely that the brain’s temporary loss of myelin is linked to these post-race cognitive declines.

However, this loss appears to be transient. As the brain recovers, myelin markers gradually return to normal levels, suggesting that this process of self-repair is part of the brain’s natural recovery mechanism. This may also point to the resilience of the brain and its remarkable ability to rebound from periods of intense metabolic stress.

Does This Mean the Brain Is ‘Eating Itself’?

While the idea of the brain "eating" its own myelin might sound alarming, it's important to emphasize that this process is not as destructive as it may initially seem. Myelin is a dynamic and adaptable component of the nervous system. The brain’s ability to temporarily use myelin as a fuel source during extreme physical exertion likely serves as a protective adaptation, enabling the brain to keep functioning during moments of nutrient scarcity. This means that the brain may be sacrificing a small amount of its tissue in the short term to preserve its overall function and ensure survival during prolonged periods of exertion.

However, it’s worth noting that excessive or prolonged myelin depletion could lead to permanent damage, which is why this process is only triggered in extreme cases of energy deprivation. In normal circumstances, the brain prioritizes the preservation of myelin, as it is vital for cognitive and motor functions. The temporary use of myelin for fuel during endurance events, while fascinating, is likely a short-term adaptive response rather than a long-term survival strategy.

Conclusion: The Brain's Amazing Adaptability

This new finding about the brain’s ability to use myelin as a fuel source during strenuous endurance exercise represents a groundbreaking discovery in our understanding of neuroplasticity. It shows that the brain is far more adaptable than we previously thought, capable of reshaping its structure and function to meet the demands of extreme physical stress.

For those involved in endurance sports or anyone who subjects their body to high levels of physical exertion, this discovery offers a fascinating insight into how the brain copes with the challenges of endurance. It also raises important questions about how our brains adapt to other forms of stress, such as aging or disease, and what this means for brain health in general.

As more research is conducted, we may uncover even more about how the brain’s metabolism works and how we can harness this knowledge to support cognitive health and performance—whether in athletes or in patients with neurological conditions.

Learn more: https://www.nature.com/articles/s42255-025-01244-7