Only if you can make it "unique" in a way which distinguishes your PIP from the rest however it is very common. NTB has made some good points and if not done in a distinguished way then it may look like that you have done your PIP in the last minute.
I also like NTB's idea about tweens and the advertising effects on pre-pubescent teens but then again I would say this is common but probably not as common as your original idea.
And scrap the obesity idea. Sorry to be clear-cut about it, but really that's another common PIP topic.
As yosemite sam said, choose a more specific topic. Whatever that is is up to you but stay clear of obesity, alcoholism, drugs, fashion. Maybe you can do a PIP topic on beauty and how 'beautiful' you are to be in order to be famous. For example, you can look at face proportions, body shape and go more in-depth with regards to hip-to-waist ratio. Also, time can be a great factor, you can compare to how beauty was in the mid-20th century compared to now. Compare say, Audrey Hepburn, to Angelina Jolie.
The above is not too good but it's just an example to demonstrate how specific you must be.