Forget cabin crew and lets generalise...........
The best looking applicants for any jobs have an edge. Like it or not it is a fact. Yes personality counts, qualifications count, etc. but if all other factors are equal the "looker" will get the job.
Take a look at any airline web site or advert - now tell me do you see any "podgy" (not my word) crew in the photos.
If you really want to get the job, i think you know that you will need to have the correct weight/height ratio. Not very PC but sorry it is a reality in ANY job you apply for but perhaps more so in the more sought after jobs such as cabin crew...................