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.
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):
“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
Pepto-Bismol is used to treat diarrhea and relieve the symptoms of an upset stomach. These symptoms can include:
Pepto-Bismol is thought to treat diarrhea by:
The active ingredient, bismuth subsalicylate, also has antacid properties that can help decrease heartburn, upset stomach, and nausea. healthline.com
Subjects treated with bismuth subsalicylate for up to 21 days have 3.5 times greater odds of preventing travelers’ diarrhea compared with placebo (95% CI 2.1, 5.9; p < 0.001). In addition, subjects with infectious diarrhea treated with bismuth subsalicylate had 3.7 times greater odds of diarrhea relief (recorded on diaries as subjective symptomatic improvement) compared to those receiving placebo (95% CI 2.1, 6.3; p < 0.001). Systematic Review and Meta-Analyses Assessment of the Clinical Efficacy of Bismuth Subsalicylate for Prevention and Treatment of Infectious Diarrhea, Brum et al 2021
Several studies have documented the efficacy of bismuth subsalicylate (BSS) for the prophylaxis and treatment of bacterial diarrhea. It is not known what effect, if any, BSS has on the normal bowel flora. We quantitated the fecal flora in healthy volunteers before and after they took BSS. In the first group, 8 ounces of BSS was given on two successive days. In the second group, a standard oral intestinal lavage preparation (GoLYTELY) was used to clean the colon and then 8 ounces of BSS was given during a 4-hour period. There were no changes in total microbial counts or in counts of individual groups such as enteric bacteria, Pseudomonas, Staphylococcus, Bacteroides, or Clostridium difficile. On day 2 the yeast counts rose 2.4 log10 colony-forming units/g in the group taking 16 ounces of BSS but did not increase in the group taking 8 ounces of BSS plus GoLYTELY. The counts returned to pretreatment levels by day 7. These results show that a 1- or 2-day course of BSS, even with an oral intestinal lavage preparation, did not have significant effects on the normal microbial populations in the fecal microflora. Effect of bismuth subsalicylate on fecal microflora, Gorbach, Cornick and Silva 1990
Microbial methylation of bismuth by the human gut microbiota has recently been reported. As the lipophilicity and thus the membrane permeability of bismuth are increased by these methylation processes, the toxic effects on human cells and on members of the beneficial “physiological” gut microbiota must be considered in medical application of bismuth-containing drugs. Medical Use of Bismuth: the Two Sides of the Coin, Frank Thomas Beatrix Bialek 2011
Bismuth subsalicylate treatment for 8 weeks (eight 262mg chewable tablets per day) is safe and well tolerated. This regimen appears to be efficacious for the treatment of microscopic colitis and is worthy of further study in a controlled trial. Efficacy of open-label bismuth subsalicylate for the treatment of microscopic colitis, Fine and Lee 1998
The present review examines the hypothesis that the mechanism of action of topical salicylates may involve protection of epithelial surfaces from colonization by certain microbes. Salicylates and the Microbiota: A New Mechanistic Understanding of an Ancient Drug's Role in Dermatological and Gastrointestinal Disease, Dammam 2013
There is some speculation that combining certain foods will cause maldigestion. The hypothesis is that different foods require different digestive processes, and a combination results in poor digestion, resulting in gas. I haven't looked into the science much, but found this article that makes a full attempt to answer this question: