I couldn't help thinking more about the story I linked to above, because the experiment it was about was really very short. They took a handful of omnivores and had them go plant-based for a short time. It would make sense that their microbiomes would take some time to sort out and get back to an equilibrium. Then too my own experience is that I am
less gassy since ditching animal-based, but I had just assumed that's because dairy always gave me horrible gas.
So I was thinking that this problem probably deserves more attention, since it seems like digestive issues really do affect some people more than others. I've been trying to read about it but it seems like it's something even the experts are still learning about.
Part of what makes it so complicated is that our microbiomes are so individual. Two healthy people can have microbiomes that look different, but obviously they both 'work'. And scientists are still trying to pin down which individual species can cause problems. There does seem to be a consensus that having a balance between different types can be beneficial.
One approach seems to be to feed the good bacteria with prebiotics (ie soluble fiber).
But that can cause problems for some people, because sometimes some of the problematic bacteria can cause mischief when a person eats or takes some prebiotics (such as inulin). I think that the idea behind the low-FODMAP diet is to actually avoid foods that cause discomfort. But I wonder if the reason they cause too much discomfort for some people is because of their own individual microbiome? I think I read somewhere that some kinds of prebiotics are better tolerated, at least in small amounts--psyllium for example, I believe.
If a person just stuck it out and kept trying to feed the good bacteria and starve the bad, would it eventually work? Or does it depend on what mix of organisms you are starting with? Would it work for some people and not for others?
Another approach is to battle the bad bacteria with antibiotics, like this small study done in Canada:
Modulation of the gut microbiota composition by rifaximin in non-const | CEG (dovepress.com)
"Of the patients, 80% (12/15) met the criteria for the key clinical end point of adequate relief of global IBS symptoms during the evaluation period. Patients with adequate relief of global IBS symptoms also reported adequate relief of bloating and abdominal pain/discomfort."
Then, too, some advocate adding beneficial bacteria (with probiotics).
Part of the idea, I think, is that adding good bacteria can help keep the bad bacteria in check. That sounds good, but there are a couple of things that can go wrong. For one, it can end up that the probiotics do a better job of living higher up in the digestive system rather than making it all the way to where they are needed in the colon. That can lead to something called 'small-intestine bacterial overgrowth' (SIBO), which can actually make things even worse. The other problem is that not all probiotics are the same. Some probiotics you can buy actually have some bacteria that are already found in overabundance in people who have digestive problems--again, making a bad problem worse.
A couple of types of bacteria that may actually be helpful are called reuteri and also bifidobacterium. There are even people who advocate using them in an enema to avoid the SIBO problem. I don't know how many people would be willing to go that far, or if it would even help. This review is about using reuteri for colic in babies, but it has been used for older people too.
Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis - PubMed (nih.gov)
One more thing some people advocate is eating fermented foods like sauerkraut and kimchi. The idea behind this is that the good (intentionally cultured) bacteria battle the bad bacteria but also this: it is actually the substances
created by the good bacteria (called 'metabolites', I think) that really get in the way of the bad bacteria over-proliferating and running away with things. So something like sauerkraut is loaded not only with the good bacteria, but also with the good metabolites it made while it was fermenting--and they both can tamp down the bad bacteria population.
This is a study done in Denmark (or maybe Norway?). Scientists wanted to know if sauerkraut would help people with 'irritable bowel syndrome' (IBS). It did reduce symptoms, even in the group that was getting the pasteurized sauerkraut. I guess maybe because the pasteurized still had the metabolites, even if the bacteria had been reduced or eliminated by the sterilization process.
Lacto-fermented sauerkraut contains a natural variety of lactic acid bacteria (LAB) and has not previously been studied in the treatment of irritable bowel syndrome (IBS) patients. The present study investigated the effect of a daily lacto-fermented sauerkraut supplement in relation to IBS...
pubs.rsc.org
If it were me, I'd try that first--pretty safe, not too expensive.
Well, I doubt Veganite's friend really wants any of my well-meaning advice, but if some other internet wanderer finds their way here looking for answers, that is my little offering.