[Help] Question about waist size and gaining?

Is it expected that your waist size is going to get bigger when on a mass diet? And if so, how much do you afford yourself as the unavoidable fat gains before you realize you're just eating too much?

I am having a hard time eating so much without feeling full/bloated all the time and feeling like my stomach is pushing against my belt. I may not be big, but the one physical attribute I have that I am proud of is my upper body-to-waist ratio. Right now I look more like Spiderman and I'd hate to lose that and just look skinny-fat, but I'm wondering if I need to go through that phase to eventually look like Thor.

Thanks in advance for any helpful input?