An evolutionary argument could be made either way:
* overweight/obesity signals access to food or ability to sustain oneself (implying also being able to sustain offspring)
* underweight could act as a handicap (showing off ability to remain on par with more well-fed competitors)
The rational thing to prefer in a mate would obviously be a "healthy body" (i.e. neither underweight nor overweight, with moderate muscle build) but it's also obvious from any good luck at human societies that that isn't always the beauty ideal.
Talking of beauty ideals: on a less than evolutionary timescale we can see shifts in preference of tan or pale skin (e.g. historically fair skin was often considered more beautiful because it signalled wealth and not having to expose your skin to the elements).
There are certainly fetishes for all aspects and variations of the human physique but blanket labelling a preference for overweight/obese body shapes a fetish seems a bit subjective -- especially if you consider that as a technical term a fetish doesn't simply refer to something you like but something you are attracted to instead of a sexual partner (as a whole).
* overweight/obesity signals access to food or ability to sustain oneself (implying also being able to sustain offspring)
* underweight could act as a handicap (showing off ability to remain on par with more well-fed competitors)
The rational thing to prefer in a mate would obviously be a "healthy body" (i.e. neither underweight nor overweight, with moderate muscle build) but it's also obvious from any good luck at human societies that that isn't always the beauty ideal.
Talking of beauty ideals: on a less than evolutionary timescale we can see shifts in preference of tan or pale skin (e.g. historically fair skin was often considered more beautiful because it signalled wealth and not having to expose your skin to the elements).
There are certainly fetishes for all aspects and variations of the human physique but blanket labelling a preference for overweight/obese body shapes a fetish seems a bit subjective -- especially if you consider that as a technical term a fetish doesn't simply refer to something you like but something you are attracted to instead of a sexual partner (as a whole).