That is a great question. It really depends on the individual gut and if they switch over 100%. Obviously if they are still putting animal products through, it’s going to be a challenge. I would recommend pre-biotics (the food healthy gut bacteria eat) in whole food form. Sauerkraut you make yourself is great (you can’t use store bought because they pasteurize it and kill all the good stuff). But all whole-plant foods have pre-biotics, including beans. I have heard some people say they used over the counter gas aids for awhile. Activated charcoal can be a short-term option, but there are side effects such as constipation. Be sure to drink LOTS of water if using them.
Another option is to try different kinds of beans to see which are easier to digest. I have found lentils to be the easiest and green peas have never bothered me. Also – if using dried beans, soak them at least overnight and rinse well (The bubbles that form on the top of the soaking water are some of what causes gas). Also make sure to cook your beans thoroughly.