Ever pushed yourself so hard during a workout that you were completely drained? Well, here's something crazy—if you're running marathons or doing high-intensity endurance activities, your brain may be literally eating itself! Sounds terrifying, right? But don't panic just yet. Scientists have learned that with long endurance activities, when glucose stores are low, your brain begins to break down its own fat stores—namely, myelin, the insulating sheath around nerve fibers.Before you swear off running for good, here's the best part: your brain is tough! This phenomenon, known as metabolic myelin plasticity, can actually keep your brain going even when you're stressed. So what does this do for athletes and fitness enthusiasts? Let's explore the science behind this strange phenomenon and how it impacts your brain health.For those who test their bodies to the limit with intense endurance training such as running marathons, there's an incredible biological process going on—your brain begins to eat itself. However, before you jump into a panic, let's see why and how this happens, what it signifies, and why it may not be as scary as it seems.Why Does the Brain Begin to Eat Itself?A revolutionary study in Nature Metabolism illuminates what occurs within the brains of marathon runners. During distance running, marathon runners exhaust their main fuel source—glucose. In response, the brain adjusts by breaking down a different energy source: myelin. Myelin is a fatty covering that envelops nerve fibers, allowing for the quick transmission of signals from neuron to neuron. This phenomenon, termed metabolic myelin plasticity, highlights how the brain temporarily repurposes its own components to keep functioning under extreme physical exertion.Researchers took brain scans of 10 marathon runners before and after a competition. Within 24 to 48 hours after the race, their brain scans showed a significant drop in myelin content, especially in white matter areas responsible for motor control and emotion integration. This self-devouring of myelin is a desperate survival mechanism, keeping the brain alive when energy levels are at their lowest.How Long Does Myelin Loss Last?The better news? The brain does not suffer permanent damage. The same research determined that levels of myelin started to repair themselves within two weeks following the marathon. But it took two months for the levels to fully stabilize. Although this short-term reduction is unlikely to lead to permanent neurological damage, it does temporarily impair cognitive function, including slower response times and reduced memory soon after severe endurance exercise.What This Means for Endurance Athletes?For decades, neuroscientists accepted the idea that the brain mostly shunned using fat as a fuel, even in dire straits. This research pushes back on that idea, proposing that myelin acts as a metabolic safety net—a backup source of fuel the brain can draw upon when glucose critically dips.The results are in accordance with existing studies on animals, especially mice, where myelin was established to be an emergency energy reservoir. Although more research is necessary to establish the long-term consequences in humans, the findings of the study are that our brains have developed the backup system in order to survive physically stressful tasks.Is it a Survival Mechanism?From an evolutionary perspective, this function may have been essential for early humans. The use of myelin may have enabled our forebears to go for prolonged periods of time on hunts without losing mental responsiveness, enabling them to pursue and catch prey over the course of many hours. The observation that highly developed regions of the brain have more myelin implies that it has played an important part in human survival and development.Possible Hazards and Consequences for Brain HealthWhile the brain's capacity for myelin breakdown is intriguing, repeated or excess myelin breakdown may have effects. Myelin is crucial for nervous system functioning, and degeneration of the myelin has been associated with neurological disorders such as multiple sclerosis. Yet, in healthy people, this transitory depletion does not appear to have significant long-term consequences.That said, individuals engaging in frequent extreme endurance activities should be mindful of their brain health. Ensuring proper recovery periods, maintaining a balanced diet rich in brain-supporting nutrients, and staying hydrated can all help mitigate potential risks associated with myelin depletion.Balancing Endurance Training With Good Brain HealthIf you’re an endurance athlete, here are some practical takeaways to support brain function while training:Prioritize Recovery: Provide your body and brain with sufficient time to recover from lost myelin before attempting another intense workout.Fuel Properly: Eat a diet filled with healthy fats, proteins, and complex carbohydrates to stay at optimal energy levels.Monitor Cognitive Performance: If you experience ongoing brain fog, memory loss, or enduring fatigue following endurance activities, seek advice from a healthcare provider.Integrate Cross-Training: Combining endurance exercise with strength training or yoga may curb extended stress to the brain and nervous system.