While I practice intermittent fasting, I do not have symptoms of IBS. Intestines get to rest when there is not food going through them.

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. Unhealthy IBS small intestines tend to suffer from inflammation and digest poorly, which results in undigested food reaching the large intestine. Not fully digested food in the large intestine causes a large amount of flatulence, and an unhealthy 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 some hours longer may allow 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. There are also some other exceptions.

My experience is that an eating window of 6 hours during the day is optimal in preventing IBS. 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 better work on repairing the small intestine if it isn't busy digesting. See the intermittent fasting article for science sources.

Related reading: Carbohydrate Maldigestion and Malabsorption, Omer and Quigley 20180801.

https://www.healthline.com/nutrition/fodmaps-101
Low-FODMAP Diet for Treatment of Irritable Bowel Syndrome, Magge and Lembo 2012
https://en.wikipedia.org/wiki/Abdominal_distension

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):
https://thehonoursystem.com/peppermint-coconut-oil-pulling-bites

“Self-reported intolerance symptoms at home are not clearly related to lactose maldigestion in elderly.” Self-perceived lactose intolerance and lactose breath test in elderly, Casellas et al, 201312
“Of the maldigesters, 63% reported symptoms and 3% of the total sample reported severe symptoms.” Prevalence of lactose maldigestion. Influence and interaction of age, race, and sex, Rao et al 199407