In my case I don't know that being "marriageable" was the issue. My mother was obese (albeit buxom and zaftig looking, which was an acceptable "look" for a woman in the 1930s, certainly preferable to looking like Twiggy which people associated with being a prisoner of war or a victim of a fatal disease)and had no trouble finding a husband and had had several lovers before that. In my case when I was growing up a lot of it had to do with class. Girls from the social class my mother had become part of (through getting a college education and marrying a professor) did not go through puberty at 10 and end up the size of Jayne Mansfield at 13. Thankfully the older I got the less important it was to be thin (as distinct from trying to maintain a reasonably healthy weight - and I don't think having a BMI of 25 or 26 is unhealthy, particularly). Most women in their 40s, 50s, and 60s are slightly overweight and men tend to prefer women who look like that, particularly if the women are curvy. I mean there's still the fashion model aesthetic, but that's not taken seriously by most people in the world most people live in.