Could the specific characteristics of some undesirable bacteria, sufferers may carry, destabilize the gut & lead to FBO & messy stools?Not that I know of.If you have sulfur reducing bacteria filling up the ecological niche that methane producing and sulfur reducing bacteria compete for your farts will have more odor than people who have methane producing (or neither) bacteria filling this niche.This does not seem to cause leaky fecal odors all the time regardless of hygeine. It just makes the farts stink. FWIW many if not most of those who have FBO problems do not see any reduction in odor from anything proven to reduce the levels of sulfurous gases from the sulfur reducing bacteria. Some do.Bacteria alone probably doesn't have a huge effect on stool consistency. I'd bet on IBS which can disrupt the progressions of stool through the colon so it only gets to the end when it is the perfect consistency. A lot of that seems to be in the control system of the gut (nervous system and some immune system cells) and I doubt any bacteria by itself can do way more to you than you do to yourself. They can participate at bit, but I doubt you could inoculate a healthy person one with one or a few species of bacteria and have that by itself cause messy stools.Although low in percentage terms wouldn't the quantity of undigested food (due to intolerance) hitting the large intestine feed these problem bacteria leading to a worsening of any symptoms?IF and only IF your symptoms are effected by gas volume. People with carbohydrate intolerances when they eat the carb they cannot digest will have a bit more carbs (in addition to all the carbs no human on the planet digests that always in every human feed the colon bacteria) for the bacteria.I know of no evidence to suggest it only feeds the bacteria you don't like. All the bacteria food is pretty generic bacteria food and doesn't specifically effect only one or two species.If I took 100 totally normal people who have no FBO, no excessive farting, no symptoms of anything and test them for carbohydrate intolerance some of them will have it and never, ever have any symptoms as they process that relatively small increase in gas volume over normal from all the bacteria food every human eats every day very well and never notice it.People with IBS often have issues with gas volume, even very normal gas volumes, and sometimes benefit from reducing bacteria food in their diet even when they have NO carbohydrate intolerances.The carb intolerance may make certain foods more problematic but they do not by themselves cause IBS, or FBO or any specific stool consistency.Would you say that consuming food for which one has an intolerance can exacerbate symptoms?If and ONLY IF you don't tolerate the gas produced (and gases from carbs are not smelly, only sulfur containing foods like protein really contribute to gas odor)Couldn't the action or waste of some undesirable bacteria destabilize the gut & putrefy its content even if its percentage volume is relatively low?If you don't tolerate the gas, you may have symptoms, but the odor you are thinking of doesn't come from carbohydrates. You like the smell of bread while it is rising, or beer while it is brewing? Carbs ferment. They do not putrefy.Would you agree that although a different environment & specifics, a typical garden compost can illustrate the possible result of undesirable bacteria.I agree some people do better with certain subsets of the normal bacteria that you find in normal humans with no symptoms of anything. The bacteria aren't doing it to you so much as how your body responds to things like gas levels may cause discomfort. There are some host-bacteria interactions but every species of bacteria you want to give the full blame to is living in other humans and causing them no problems at all.