anything with lots of fiber should do the trick, like beans or flax seed ( my favorite because its very obvious when they clear the system) ive been doing 80 h fasts and i go very randomly now. its like my digestive system is taking much longer to digest the exact same thing i used to eat regularly ( once it was 3 days with no poo on a 4 day fast)it really depends where you are getting your 1500 calories from i think.
im pretty sure if you have gas your digestive system is still working right.. just slowly. i always have some gas. but then my brake fast is usually beans lentils flax and rice then i am back on the fast
in the mornings I drink two to three cups of water a little bit more than warm but not too hot that you cant just chug a cup of it. After the second cup, my stomach be making noises and by the third cup im running for the can and it makes me poop. Not to be graphic but thats what works for me. During the day I also chug water, so if I drink water Im not drinking just one of those tiny water cooler cups, im drinking like six cups of those tiny water cooler cups guessing theyre like 6 ounces a pop. Hope this helps