Fat chicks have more sex

In all species in which the female makes greater parental investment into the offspring than the male does (including humans and all mammals), mating is a female choice; it happens when the female wants it to happen and with whom she wants it to happen, not when the male wants it to happen or with whom he wants it to happen.

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Their statistical analysis shows that there is no significant difference between normal-weight women, on the one hand, and overweight and obese women, on the other, on their sexual orientation, age at first intercourse, frequency of heterosexual intercourse, and the number of lifetime or current male sexual partners. It means that, contrary to what one might expect, overweight and obese women are not having sex later, less frequently or with fewer partners than normal-weight women. There is a significant difference, however, on whether they have ever had sexual intercourse with men. Overweight (92.5%) and obese (91.5%) women are significantly more likely ever to have had sexual intercourse with men than normal-weight women (87.4%).

Psychology Today

If you give it away, there will be takers, but you may have to lower your expectations. These are the kind of people having that awesome neurotic sex they tell you about in Hollywood and celebrity magazines: bloaters, mental defectives, etc.

Women with options know their value and don't give it away. Same thing is true of men; those who are going somewhere in life aren't going to take some bloater up on her offer of free intercourse. They're going to direct their energy down more productive paths with less of a risk of having a half-walrus offspring.