I used to go for a walk a lot, my body had developed well, but since I've only been sitting around at home on my mobile phone / laptop, am I developing?

No more. Do you think it has something to do with the fact that I don't go for a walk anymore?

Yes, with what else?

You could say it like this.

I always notice that when I come back from a long walk or one of my pathetic jogging attempts, I somehow feel like eating fruit or something instead of chips and sweets. If, on the other hand, I just sit at home all day, it's the other way around

That doesn't grow anymore either?

Maybe not