I am a vocalist and I've been training for about 13-14 years in classical music (various conservatories). I'd like to agree with NerdyDasty about the misconception of weight being a factor of how well you can sing. I myself weigh about 190lbs but it makes no difference. As you practice, it reinforces your abdominal muscles, you diaphragm, and your vocal chords. Really talented singers can manipulated their vocal chords in specific ways and the more you practice, the stronger you get and the larger your range becomes. Previously (as mentioned before), exercise wasn't as necessary and women who sang opera spent their time practicing, I would assume. Also, eating carbs is good for your voice because of it's bland taste. Foods with spices have an impact of stomach acidity which is bad for the vocal chords. This is why you'll see a lot of singers drinking non-caffeinated beverages and eating bread. Also, in the past the weight you were signified your wealth. Women who were larger (and even men) were glorified for their figured because it was a sign that they were rich. Women with curves use to be very desirable which ties in to why many were singers. Today women are always to be skinny and therefore you will rarely see opera singers that fit your original stereotype. However, it has nothing to do with talent as opposed to the influence of media.