At the danger of moving the debate on....
BMI (that's Body Mass Index) is probably a better measure than absolute girth. Equally, when (if???) you go to the gym, they're likely to have a chart which shows the healthy range of weights for a given height. For example, try this link:
Height against Weight
Something on these lines could be used as a sensible basis for recruitment. Weight in proportion to height is used for pilots (certainly at the initial medical), why not cabin crew? I'm 6'1" and 180lbs without getting paranoid about what I eat. If I can do it, anyone can.