... 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.
The article doesn't explain how it's not a bad thing.
In other words, their brains did a little temporary damage to themselves to protect their overall health in the long run.
It says that the brain's fatty tissues seem to return to normal eventually. It feels like saying that an overuse injury isn't a bad thing because you can recover.
I agree with you, in the article it doesn't explain at all how it's not harmful. One of the proposed benefits of fasting is autophagy - it's thought that the body "eats" your diseased, damaged or less healthy tissue first when you don't eat. I really don't know if that's true but undereating & fasting is generally healthy as long as you don't do it all the time or get too thin. And overeating is harmful, so it does seem logical that it's beneficial for your body to sometimes get a chance to eat itself, that you shouldn't always feed it.
Fun fact most of the under eating studies on mice longevity are actually intermittent fasting studies in disguise. When underfed the mice eat all their food immediately when fed... And then don't eat at all until the next days feeding.
Those grad students are not feeding the mice one pellet every hour.
Like shredding a muscle so it knits back stronger?
Is this not why long form runners take those gel packs or whatever I always thought it for like mid run energy or something.
Those are just sugar to help muscles. If you do any high intensity activity for more than 2 hours without rest, your body will begin to consume itself.
Of course if the runners are on a low carb diet for 6 weeks... They don't run out of glucose while running, as they are burning mostly fat.
Fat adapted athletes don't bonk or hit the wall.