I remember watching Running Man back during their first year airing, which was around 2010~2011 episodes.

There was a segment where the cast members doing a mission involving adding their total weight together (3 person per team) and Song Ji Hyo and the other 2 male members did their weight measure together.

So after they read the total weight, the 2 guys talked with each other and deduced that Song Ji Hyo weight was over 50kg, which surprised her that they knew her weight just from that.

So she denied having her weight over 50kg and jokingly said that her clothes and shoes added to her weight which is why it was over 50kg. This was a recurring joke later on other episodes.

If you watch the recent female idol group or celebrities, some of them even weigh less than 40kg which is scary and could result in health issues.