While I practice intermittent fasting, I do not have symptoms of IBS. Intestines get to rest when there is not food going through them. Also, undigested food is held for a longer period in the small intestine, if there is not more food coming along the way. This allows the small intestine to fully digest the food before releasing it to the large intestine, which results in avoiding excess flatulence and having a healthier microbiome.
Food can make it to the large intestine in as little as 6 hours after consumption. If you have two meals spaced 4 hours apart, the food from the first meal will continue to be digested in the small intestine, even after the second meal is consumed. However, waiting longer allows the first meal to travel further along the small intestine, such that the second meal may trigger the release of the first meal into the large intestine, before being fully digested. This also can happen from over-eating.
It's also important not to eat before bedtime, because your body repairs itself during sleep, especially during the deep sleep cycles that happen in the first few hours of sleep. The body can work on repairing the small intestine if it isn't busy digesting.
Eight studies show that peppermint oil helps with the symptoms of IBS. See the details in the examine article. Update: they used to list all the studies, and now you need to pay subscription to access the full list
Coconut oil pulling bites (with peppermint):