By Tarun Sai Lomte Reviewed by Susha Cheriyedath, M.Sc. Mar 25 2025 Researchers uncover a surprising side effect of marathon running—temporary loss of brain myelin—hinting that the brain may burn its own insulation for energy during extreme physical stress. ​​​​​​​ Brief Communication: Reversible reduction in brain myelin content upon marathon running . ​​​​​​​Image Credit: Real Sports Photos / Shutterstock In a Brief Communication published in the journal Nature Metabolism , researchers