ananyo writes "A trip to the gym could mean not just losing pounds — but also chemical modifications from DNA in the form of methyl groups. The presence (or absence) of methyl groups at certain positions on DNA can affect gene expression. Researchers at the Karolinska Institute in Stockholm looked at the methylation status of genes in small biopsies taken from the thigh muscles of healthy young adults before and after a stint on an exercise bike. They found that, for some genes involved in energy metabolism, the workout demethylated the promoter regions (stretches of DNA that facilitate the transcription of particular genes). Genes unrelated to metabolism remained methylated. Furthermore, similar demethylation could be seen when cultured muscle cells were given a massive (probably lethal) dose of caffeine."