Exercise not only builds muscle and burns fat, it also changes your DNA, a new study finds.
Researchers, reporting in the journal Cell Metabolism, said laboratory experiments have found that when sedentary people start exercising, it produces an immediate change in their DNA – from the very first workout. The study also found that the caffeine in coffee appears to have the same effect on DNA in muscle tissues.

Working out doesn’t change a person’s underlying genetic code, but the DNA molecules in muscles are chemically and structurally altered by exercise, explained researcher Juleen Zierath of the Karolinska Institutet in Sweden. Those modifications appear to be the way exercise leads muscles to gain strength and boosts metabolism.

"Our muscles are really plastic," said Zierath. "We often say ‘You are what you eat.’ Well, muscle adapts to what you do. If you don't use it, you lose it, and this is one of the mechanisms that allows that to happen."

The new study found specific changes in DNA molecules in muscle taken from the legs of 14 young men and women after a burst of exercise on a stationary bicycle. Those changes take place in stretches of DNA involved in turning "on" genes important for muscles' adaptation to exercise.

When the researchers made muscles contract in lab dishes, they saw similar DNA changes. What’s more, caffeine had the same effect on muscle tissues.