This may sound stupid but can slouching cause belly fat?

it won't cause belly fat. eating more than you burn off causes belly fat

however, poor posture can lead to untoned abs muscles (as well as other musculo-skeletal problems) and they may sag and make it look like there's more belly fat than there is

solution: do exercise that works your whole body, including your core/abs, and also eat at a calorie deficit. i.e. tone up your whole body, including abs, and lose the belly flab through eating less than you burn off

Poor posture gives you the appearance of having more belly fat, and having good posture and a strong core can help reduce that.

^^^This.

They are right. It won't cause belly fat, but may cause the appearance.

The good news is, it's a quick and easy solution. Stand up straight, tighten those tummy muscles, and voila, trimmer looking abs :happy:

(I agree with what neandermagnon said … posture is important for many other reasons, especially avoiding back issues later in life, and it's important to build a strong core )