Researchers find brain may feed on itself during marathon running

• A new study suggested that the brain may temporarily break down its own insulation to fuel extreme physical efforts, such as marathon running. This process is thought to be reversible and may highlight resilience.
• The study used advanced MRI imaging to scan the brains of 10 marathon runners, finding reduced myelin content in specific areas two days after the race.
• The study’s findings have implications for understanding how the brain adapts to physical stress and may inform treatment for demyelinating diseases like MS.

---

Full Story

A new study from the journal Nature Metabolism and researchers at CIC biomaGUNE, a biotech research institute in Spain, suggested the brain may temporarily break down its own insulation for fuel during extreme endurance efforts like marathon running.

While the effect appears reversible, scientists said it raises new questions about how the brain manages energy under intense physical stress — and what that might mean for people with neurological conditions.

What is myelin, and why would the brain burn it?

Myelin is a fatty substance that wraps around brain and spinal cord nerve fibers. It acts as insulation, helping electrical signals move quickly and efficiently between brain cells. It is also energy-rich, and that may be key.

When the body runs out of sugar during prolonged physical exertion, it turns to fat stores for fuel. The study’s authors said that those fat stores in rare cases like a marathon may include the lipids in the brain’s myelin.

How did researchers measure changes in the brain?

The research team scanned the brains of 10 marathon runners using advanced MRI imaging, capturing images 48 hours before the race, then again two days, two weeks and two months after.

Two days after the race, they found reduced myelin water fraction (MWF) signals — a marker linked to myelin content — in 12 specific brain areas, including regions tied to motor coordination and emotional regulation.

In some areas, MWF dropped by 28%.

Does the brain recover from this loss?

Yes. MWF levels returned to their pre-race baseline two months after the marathon.

The study’s authors describe the process as “metabolic myelin plasticity” — a short-term shift in how the brain accesses energy under strain.

They found no signs of lasting harm in the healthy runners studied.

Could this affect people with neurological conditions?

While the process appeared harmless in this small group of healthy participants, researchers said it could have different implications for people with diseases like multiple sclerosis, where myelin damage is permanent.

The study raised questions about whether extreme endurance exercise could pose added risks for individuals with conditions such as MS or ALS, which affect myelin and motor pathways.

More research is needed to explore those outcomes.

Should runners be concerned?

The study didn’t suggest marathons are dangerous for healthy individuals.

If anything, researchers said it highlights how resilient the brain can be. But it also opens new avenues for studying how the brain adapts to physical stress — and how that adaptation might inform treatment for demyelinating diseases.

The findings offered a glimpse into how flexible — and vulnerable — the brain may be when pushed to its metabolic limits.

Editor’s note: This article is for informational purposes only and does not constitute medical advice.