Gaining

If you don't believe in evolution, I can't help you. If you do, I can think of several reasons why these fetishes would be adaptive:

1. Low birth weight babies are more likely to die in childhood. Larger women are unlikely to have low birth weight babies, even in times of food shortages. In many scenarios, men attracted to such women (FAs) would be more likely to reproduce.

2. In some societies, it may be difficult or even impossible to become overweight except for powerful men. Women attracted to such men (and their children) would have reproductive advantages.

3. In The World Until Yesterday: What Can We Learn from Traditional Societies? Jared Diamond describes traditional societies that go through cycles of food shortages and food surpluses. They gorge during the times of plenty to gain weight to help them get through the lean times. Feedism would be adaptive in such societies as it would encourage that behaviour.

Of course, in other societies and scenarios these fetishes are probably maladaptive. Everyone inherits a different genetic mix of these fetishes. Also, in most cases, these tendencies are probably activated (or not) by one's particular experience.

I.e., we're all different!

I also believe that this is evolutionary: Lets not forget that this fad for thinness is very short lived:
Fat was the most attractive way to be for millenia, while this obsession with thinness is only 100 to 200 years old.
I agree wholeheartedly with Dr. Feeder, in the old times being fat was a huge advantage, because you would survive bad times, while your thinner contemporaries starved to death.

Also, being fat means that you can have kids and even lose weight in bad times but then still have reserves. Our propensity to gain weight shows that the body liked that life insurance and that you could end up dead real fast when times got lean and you had to go for a whole year without much food.

I would not be surprised if animals become more fertile when they are fatter and have lots of food (which is the same for the body) and less fertile when they get thin (which means that food is rare).
You just have more resources to work with, overplenty and overflowing means also overflowing life force and offspring and hope for the future. And in the end, life force and energy equals sexual energy.
And getting horny by eating is that, the body knows it has a lot of energy, so lets procreate.

My theory would be that we feeders and feedees have the part that controls sexual energy very very old, from back then, when all men found fat women the most attractive or wanted to grow fat themselves, just because it means incredible wealth and also security for your life, that you would go on and keep living.

And feeders and feedees don't get confused by the media, don't get influenced by the fat shaming and all that blablablabla about losing weight and that fat is ugly. We just don't buy it, we KNOW that fat is sexy and sensual and the most attractive, naturally.

For me a feeder or feedee is a FA that is very very sure of what he/she believes: we don't just accept fat or merely love it, we worship it and logical conclusion: want more of it. Why wouldn't you?

If you like money, why not have more money? House? Have more housing space!
In pretty much everything, more is better and in weight and body size, that is the same.

If you have somebody you love, why wouldn't you want more of them, that they are more person?

Actually I didn't say that. The reality is more complicated I fear.

While SOMETIMES being fat is an advantage, e.g., in times of food shortages, a lot of the time it isn't. E.g., it's harder to hunt, flee from your enemies. So obesity and attraction to it has varied a lot over the years and between societies. Really, storing energy as fat is pretty inefficient. It's better to store food and stay thin if you can.

So what I'm saying is the human race is a mix of tendencies to gain and not gain. Feedists happen to have inherited more pro-fat tendencies than other people, and likely have gotten certain environmental triggers to get that going.

Sorry, did not want to misquote you.

Well, if you are fat, you don't need to run and hunt ;-)

You can sit home and work on better tools to hunt, you don't have to constantly be on guard and fighting to survive and not starve.
So after a time of plenty when everybody could eat themselves fat, the pressure was off compared to when you are thin.

Fat is after all energy reserves. We got that, after life taught us that having no reserves is deadly if you have to run for months and maybe years without food.

There are times and places where it's better to be fat, and times and places where it's better that some people are fat and some aren't.

But if you're saying it's ALWAYS advantageous to be fat I'll respectfully disagree. Maybe we can debate it at the next meet-up!