I don't know if they're natural. They're like fiber supplements for older folks (like metamucil or something) but I couldn't tolerate drinking that stuff so I bought them in tablets and they really did help with that full bloated sick feeling. They're not like a laxative either -- well they are -- but a very mild-acting one, it took 3 days.
See, I think the nicotine acts as a laxative, or your body becomes dependant on it in more ways than you realize because I have not been normal in the digestion arena since I quit 3 months ago and I didn't change the kind of foods I eat. I did start eating more of it though. I have a terrible fast food diet, I'm sure that doesn't help, but I've been trying to cook at home more often, It still didn't help.
Thing was, when I was all bloated and constipated I still felt hungry. Sick and hungry, and taking care of the constipation problem helped take care of that sick stomach hungry feeling and also now I have more energy to exercise and stuff. I'm not so tired and sluggish all the time.
Don't know if this will help you but it's worth a try -- get the tablets at the grocery store, they are not expensive at all.