If you’re into really strenuous endurance exercises that push your body and mind to the limits, like running marathons, just know that at some point during all that exertion, your brain will start to eat itself — and it’s not necessarily a bad thing.
A study published in Nature Metabolism found that people who regularly participate in long-distance endurance events like marathons tend to run low on glucose in the middle of the event, which forces the brain to start chewing up a fatty substance called myelin that surrounds nerve fibers and helps neurons transmit signals.
The researchers call this process “metabolic myelin plasticity,” a fancy scientific way of saying that your brain has chosen to eat something other than its typical sugar for fuel.
The researchers scanned the brains of 10 marathon runners before and after a race. In the 24 to 48 hours after a marathon, the researchers found big changes in the amount of myelin in their brains’ white matter, specifically in regions related to motor function and emotional integration.
So much myelin had been depleted that it took two weeks for it to start coming back and a whole two months after the marathon for the numbers to stabilize. In other words, their brains did a little temporary damage to themselves to protect their overall health in the long run.
This is kind of a big deal since before this, we assumed that the brain leaves its fatty reserves alone if it’s starving for energy. We now know that, under extreme conditions, it absolutely will start eating at its all-important fat reserves.
Thankfully, the loss of myelin is temporary, and the effects of that loss seem to be mild at best, which is good considering that myelin is vital to the day-to-day functions of our nervous systems. If we suffered too much loss, we could find ourselves stricken with a variety of neurological diseases, multiple sclerosis among them.
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