You and I both want to know! I don't have all the answers, but I'd like to share some of my thoughts on this, since it is one of the most frequent queries I receive. I look forward to reader and professional comments on this one.
I think we can all agree that bacterial fermention in the gut is normal and desirable to a certain point. The bacteria in our guts have their own jobs to do for us, and they have to eat--fermentation is how they do it. This normal state of affairs can be disrupted by illnesses, infections, use of antibiotics, or food intolerance or allergies. If too much gas is produced as a result of bacterial imbalance, it can be part of the IBS picture
Or, the bacterial fermentation piece might be perfectly normal, but your nervous system may be so sensitive that you experience normal gas expansion of the colon and abdomen as a painful sensation.
When we use a FODMAPs restricted diet we deprive certain gut bacteria of their favorite foods. This decreases gas production. But we don't want to give up the health benefits of the short chain fatty acids (SCFAs) and other substances that gut bacteria produce for us.
A key point is that each species of bacteria has its own favorite food, and produces a unique combination of gases and SCFAs. People with IBS (and eating a FODMAPs-restricted diet) need a gut stocked with critters that like to ferment non-FODMAPS carbohydrates, don't produce gas, and do produce large amounts of desirable SCFAs. Oh, and it wouldn't hurt if they could also control gut pH, help the immune system function properly, and "box out" bad bacteria. And they should be safe, of course. Bifidobacteria appear to be the best candidates.
Enter probiotics. When we take probiotic supplements we are ingesting microbes that we think will help, in large enough quantities to have a medicinal effect. Probiotics in general show a lot of promise for treatment of IBS, but we have much, more more to learn about them. Specific probiotics that have been studied and have evidence showing a good treatment effect are: Bifidobacterium infantis (best), Bifidobacterium animalis, and VSL#3 (a patented blend of different species of bacteria).
People who are immunocompromised (due to illness or immune-suppressing drugs) or who are critically ill should not take probiotics without discussing the risks and benefits with a health care provider.
My next post will cover the nitty-gritty of how and when to take probiotics when using my FODMAPS-elimination diet program. Stay tuned!