In the Economist:
As doctors never tire of reminding people, exercise protects against a host of illnesses, from heart attacks and dementia to diabetes and infection.
How it does so, however, remains surprisingly mysterious. But a paper just published in Nature by Beth Levine of the University of Texas Southwestern Medical Centre and her colleagues sheds some light on the matter.
Dr Levine and her team were testing a theory that exercise works its magic, at least in part, by promoting autophagy. This process, whose name is derived from the Greek for “self-eating”, is a mechanism by which surplus, worn-out or malformed proteins and other cellular components are broken up for scrap and recycled.
To carry out the test, Dr Levine turned to those stalwarts of medical research, genetically modified mice. Her first batch of rodents were tweaked so that their autophagosomes—structures that form around components which have been marked for recycling—glowed green. After these mice had spent half an hour on a treadmill, she found that the number of autophagosomes in their muscles had increased, and it went on increasing until they had been running for 80 minutes.
To find out what, if anything, this exercise-boosted autophagy was doing for mice, the team engineered a second strain that was unable to respond this way. Exercise, in other words, failed to stimulate their recycling mechanism. When this second group of modified mice were tested alongside ordinary ones, they showed less endurance and had less ability to take up sugar from their bloodstreams.