Marathon runners’ bodies appear to be devouring brain tissue, scientists say

November 7, 2023

Talk about using your head. In a recent—although yet-to-be-peer-reviewed —paper, scientists posit that marathon runners’ bodies might turn to brain tissue as a mid-race energy source, gobbling down the mind’s protective myelin layer and turning it into fuel, reports Futurism.

Myelin is a fatty tissue found in our body’s nervous system, coating our brain and nerve fibers in an extensive casing of insulating plasma known as the myelin sheath. And importantly, as Klaus-Armin Nave, a neurobiologist at Göttingen, Germany’s Max Planck Institute for Multidisciplinary Sciences—who was not involved in the study—recently told Science News, it’s long been “thought that myelin sheathes were assembled, inert structures of insulation that don’t change much after they’re made.”

In other words, myelin sheathes formerly were widely thought to be unchanging structures with a single job to do. But according to the paper—published in early October as a preprint—before-and-after scans of a handful of marathon runners’ brains tell a different story: that myelin is a dynamic and adaptable tissue that’s not only available to the body as a reserve energy source during prolonged physical exercise, but also as a replenishable source of fuel to boot.

The study itself was fairly simple. Led by Carlos Matute, a neurobiologist at the Achucarro Basque Center for Neuroscience at the Leioa, Spain-based University of the Basque Country, the scientists took images of four marathon runners’ brains in the 48 hours leading up to, and in the 48 hours after, a big race.

As it turns out, the before-and-after differences in myelin levels appear to be quite drastic, with the “after” scans showing stark declines in the insulating tissue—a finding that seems to support the hypothesis that the runners’ bodies looked to their brains for an extra hit o’ juice to get over the finish line.

“This is definitely an intriguing observation,” neuroimaging scientist at the National Institute on Aging in Baltimore Mustapha Bouhrara, who was not involved in the study, told Science News of the research. “It is quite plausible that myelin lipids are used as fuel in extended exercise.”

Perhaps most fascinating, however, is what appears to have happened in the brains of some of the runners in the weeks following the race. According to the study, when the researchers scanned two of the original four marathoners’ heads two weeks after the 26.2-miler, they found that the runners’ depleted myelin appeared to have bounced back in full, suggesting that the stuff is much more adaptable than previously thought.

There are a few notable caveats to this research. Again, it’s not peer-reviewed and four people isn’t a particularly large sample size. There’s also a chance that the depletion seen in the scans is actually a case of dehydration—the channels between myelin’s lipid bilayers are packed with water—although the scientists involved in the study seem pretty staunch in their opinion that dehydration has nothing to do with the changes.

“In our opinion, this is not the case,” Matute told New Science, noting that the 48 hours between the race and the following scans would have given the runners enough time to rehydrate. Another sign that dehydration wasn’t the culprit? Like a dried sponge, a dehydrated brain will shrink; the runners’ scans, said Matute, showed nothing of the sort.

“We saw that there is no shrinkage of the brain at all,” the scientist told New Science.

The paper is very preliminary, in other words, but its findings are thought-provoking, especially considering how little we actually know about our own brains. Hopefully this research warrants future research into the unlikely dynamism of the myelin sheath—and whether marathoners are the only folks who might be tapping into myelin as an energy source.

Research contact: @futurism