Haruki Murakami, the excellent Japanese novelist, wrote about the sign inside his Japanese gym. It was something like,
"Fat is easy to get and hard to lose. Muscle is hard to get and easy to lose. Such is life."
It's similar to another Japanese expression about money --
"Getting money is like digging in sand with a needle, spending it is like water soaking into sand."
I remember where I read the first quote -- it was reading "What I Talk About When I Talk About Running" in 2008, when I was in Barcelona and living near Placa Espania. At the time, I happened to be on a fantastic routine of waking up at 4:30AM, reading and eating in a little Spanish shop that served a fantastic Spanish egg/potato/vegetable omlette until my gym opened, spending a couple hours in the gym, and then working until dinner before sleeping early.