There has been some good research on male and female body shape preferences and, more interestingly, what each gender thinks the other prefers.
The finding is that women (especially Caucasian women) are far more likely than males to consider themselves heavier than the ideal, and also consistently think that men prefer a thinner figure than the preference actually indicated by men.
Men, on the other hand, tend to be happy with their body shape and to think women prefer a bulkier form than women actually indicate as their preference.