I think I heard mentioned on art classes that fat equaled wealth, and so fat ladies might be desirable.
But you have a point.
I had a Bangladeshi friend explain to me ~8 years ago that all the female Bangladeshi movie stars (not to be confused with Bollywood stars) were fat. For most of the population, being thin was a sign of not being able to afford much food, so fat women were the ideal. Just goes to show how subjective certain kinds of beauty are.
Ditto, a couple of hundred years ago being pale was fashionable - it meant you were rich enough to not work outside. Nowadays of course, we mostly work indoors - so being tanned is fashionable.
It depends on where you are. I spent 6 months in Jakarta, and due to cultural arbitrage, was able to date incredibly attractive women there because I was pale and fat, and I tend to go for women with darker complexions, who are considered ugly due to the same "working outside" cultural bias.
It's true in a lot of cultures. I know in pre-colonial Hawai'i, being huge was attractive. I hear it was true in parts of Africa, too. It's not true in the states just because the bar isn't that high to get 2-3k calories per day. I think it's generally true that standards of beauty follow whatever implies a higher standard of living. Look at America today: facial and hair complexion to show quality, not just quantity, of food; muscle tone and tan to show spare time out of a desk job doing exercise; and of course flamboyant displays of money, the ultimate objective measure of success.