Casually Walking:
Technically everyone has it, let me explain
It is widely believed that every single person will develop a want for a bigger partner under stress, because eons ago, when humans didn’t have an abundance of resources, stress usually came with a drought or a bad harvest, which meant someone larger had food
In the sense of the people who’s preference never “turns off”, well, that’s more difficult to gage, someone would have to go around asking everyone if they like fat, being fat, or any other relation to the fetish. And I’m sure a lot of people wouldn’t admit it due to the stigma surrounding beauty
Bellyempire:
So perhaps fat fetishism is based on stress in childhood
The theory that when under stress you desire a larger partner on a primal level is, as mentioned, widely held. It's not only an indication that they likely have access to more food, but also seen as an indication they are stronger and more likley to be able to protect you, and also likely healthier and able to produce and care for offspring. It's a survival thing.
However, I think stress in childhood is less likely to be the reason for becoming a chubby chaser or gainer, and more likely a cause for eating disorders developing, and eating disorders aren't the same as feederism and fat fetishism. They are very different and separate things that for some people may have an overlap, but I think it's a stertch to say that all cases of feederism and fat appreciation/admiration/fetishism stemmed from childhood stress.
Not every person that is into feederism or weight gain has an eating disorder, and there are an awful lot of people with an eating disorder that are not into feederism or weight gain at all and hate what their eating habits do to their body.
I think it's more likely that the kinds and sizes of bodies we are attracted to is just part of who we are, in much the same way that whatever gender we are attracted to is just part of who we are, and it's social conditioning that makes it taboo and in turn makes people feel ashamed of their attraction. I've no doubt there are swathes of people out there that hide and suppress their attractions and desires because they are terrified of being judged and ridiculed if anyone were to find out.
