Opera singer checking in.
Aside from the fact that most are very vocally gifted, any generalization you can make about opera singers is worthless.
Indeed, some are overweight. Indeed, many are not. In my personal experience (having gone through multiple training programs and participated in numeous professional productions), the percentage of obese individuals among opera singers is lower than that of the general adult population, at least in America.
There is no aspect of being an opera singer that presents an absolute barrier to physical fitness or general health. Excercise, when intelligently done, does not harm the voice, and the travel, rehearsal, and social obbligations of singing are similar to other professions that require frequent travel and odd hours.
There are just as many hotties as horses in opera, and the percentage of hotties is larger than in the general population, especially among women. So-called “unattractive” (not tall, not handsome, not in shape) men have a better chance of succeeding than supposedly unattractive women because there are fewer men in the field and therefore they are in greater demand.
Opera’s reputation for having fat stars comes, quite mundanely, from the fact that being fat or plain does not disqualify one from succeeding in the field, which distinguishes it from film and contemporary pop music. It is an obstacle, though. A person has to have extreme talents to avoid body type descrimination. I am currently encouraging one of my more talented students to go on a disciplined weightloss program for just that reason. He has the talent to succeed, but it will be easier if he gets in shape.
Finally, I’m 6’3’’, 190lbs. I had moderate success as a singer before moving into more teaching and other professions to pay my bills. Never once was I cast, or not cast, for my looks.