Marathon runners use brain cell insulation as a source of energy for the race

Marathon runners use brain cell insulation as a source of energy for the race

A fatty substance that insulates the electrical signals transmitted by nerve cells could also be a source of energy for the brain - especially when reserves are running low. This intriguing possibility was revealed by scans of long-distance runners' brains taken before and after marathons.

The scans indicate that the levels of the insulating substance – called Myelin – in brain regions responsible for motor control and sensory and emotional processing decreased after the strenuous events, only to return to normal levels within two months of the races.

Although the idea that myelin acts as an energy source is not entirely new, no one had thought to study it in runners, says Carlos Matute, a marathon runner and neuroscientist at the University of the Basque Country in Leioa, Spain, who led the study, published today in Nature Metabolism 1. “These results raise the possibility that myelin lipids contribute to brain energy processing, at least under certain conditions.”

The temporary loss of myelin after a race shouldn't cause concern from a runner's perspective, adds Matute. His team is currently conducting studies to examine whether reducing myelin has a temporary effect on cognitive function, and so far there have been no results indicating significant effects, suggesting that the effect is either very small or non-existent. “There are no gross changes in brain function,” he says. In fact, Matute suspects that utilizing and replenishing myelin is beneficial because it trains the brain's "metabolic machines."

Mustapha Bouhrara, who studies brain scans and aging processes at the US National Institutes of Health in Baltimore, Maryland, agrees. The loss of myelin only lasts a short time and is therefore not worrisome, he says, and the process teaches the brain how to repair myelin quickly and "could be very, very beneficial."

Matute, who has run 18 marathons, came up with the idea for the study during his training. He wondered how people could complete such demanding races. Given the abundance of myelin in the brain - it makes up up to 40% of the central nervous system by weight - and its fatty composition, Matute wondered whether the brain could use the substance "strategically" to continue functioning when other energy sources dwindle.

His team used magnetic resonance imaging (MRI) to determine the Brains of ten runners - eight men and two women - within 48 hours before and after their participation in various marathons in Spain in 2022 and 2023. The authors found that myelin levels in 12 brain regions were significantly lower after the race than before. “It wasn't much, but it was a significant reduction in certain areas of the brain,” says Matute.

The affected areas are responsible for motor coordination, sensory perception and emotions and are regions you would expect to see active during a marathon, explains Matute. “We feel a lot of things while running and often need to motivate ourselves to keep going,” he adds.

The researchers re-examined the brains of some of the runners in the weeks and months after the races. They found that some “remyelination” had occurred after two weeks and that myelin levels were fully restored after two months.

1. Ramos-Cabrer, P. et al. Nature Metab. https://doi.org/10.1038/s42255-025-01244-7 (2025).

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2. Asadollahi, E. et al. Nature Neurosci 27, 1934–1944 (2024).

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