I do feel that our profession (like firemen, military, etc) does stand to benefit from a public image that inspires confidence. The heavier boyz and girlz should do themselves and us a favor and improve their lifestyle. However...

Many airlines screen (formally or informally) for BMI and many other health indicators. HOWEVER...this is NOT done in any way, shape, or form with the safety interests of the travelling public in mind. It is done for two reasons
1) Liaibility cushion "well we checked his cholesteral when we hired him"
2) Minimize the likelhood that an employee will take expensive medical/disability leave in the future.

EVERY single company in the world would like to do #2, but it's highly illegal. The ONLY reason the airlines have been able to fight off the lawsuits on this subject is because it's easy to bamboozle twelve of our "peers" with talk about flight safety. Many airlines just verify that you have a current first class...are they measureably less safe? I doubt it.