Not surprising to me

Heavy girls likelier to have sex early: They're also less prone to use birth control, study shows

Certainly in terms of self-esteem, overweight and obese girls tend to have lower self-images than others, and that puts them at risk for being pressured to have sex without preparing properly for birth control. The need to feel special and to have external validation is common among people with low self-esteem. If someone gives a girl with low self-esteem attention, I think she will be more likely to latch onto them emotionally and do whatever it takes to keep them with her. That's certainly my experience. I didn't lose my virginity until I was a sophomore in college, at 18, but I had such low self-esteem that I really gave my brain over to the first person who said he loved me and felt I had to marry him to be a 'good girl'. I left the marriage 6 months in (but after 6 years together) because I finally came to my senses.