IBS and vegetarian diet?

The least-gassy legume product in my experience is tempeh. The history is interesting. It comes from Indonesia where a fungus called oligosporus was domesticated and harnessed for fermenting legumes. Tempeh is most often made with soy, but can be and has been made with almost any other legume. You can even buy tempeh culture online and culture your own beans, but they should have the skins taken off them first because the mycelium can't get past the tough bean 'jackets', so that limits the home-culture hobbyist to beans that you can buy with their jackets off (like mung beans in some specialty or ethnic markets) or to taking the skins off yourself. When it is growing it looks like a grade school science project-- lots of fluffy white mold! This condenses down into something that looks less frightening after it is boiled.

Mushrooms (another fungus) have been touted by some as one of the foods that may fend off Alzheimer's. Could the fungus in tempeh offer similar benefits? I hope so, because I enjoy it often.

The tempeh you buy in the store has been vacuum-packed to keep it fresh. It almost always has a bitter taste that puts most people off. I seem to be rather impervious to bitter tastes and can enjoy tempeh simply braised, but better cooks than me have written about ways to make it more appealing.

Another option I've tried is a modern variation on traditional East-Indian foods like dosas. The basic formula is to soak beans or lentils for a few hours (again, without skins on them, such as red lentils), drain and rinse again, puree in a strong blender with just enough filtered (chorine-free or chlorine-reduced) water, pour into a very clean (preferably sterilized) glass container with plenty of room for it to expand, stir in a very good probiotic pill, cover loosely (with a glass plate for example), and ferment several hours in a warm place, like a dresser drawer lined with a heating blanket on the lowest of 4 settings (you don't want it too hot)-- or just anywhere warm, like in the shade on a very warm day. It gets bubbles in it and separates a bit, liquid on the bottom and fluffier on top. Stir to even that out. Then add any desired flavorings and cook like thin pancakes or crepes.

Traditionally dosas are made with both legumes and grains fermented together. That probably helps with taste and texture. I've done both ways. You can find lots of bloggers writing about either tempeh- or dosa- making, if you or other cooks you know are interested.

It may sound intimidating, but if I can do it anyone can! You just need to do some research beforehand to learn what to expect. If anyone is interested, I'd be glad to try to answer any questions.

Also, have you already tried things like bean-o and gas-x?

Yes and they help somewhat with discomfort and prevention - I also take IB Gard (peppermint oil capsule) when I am going to eat something that can be difficult for me to digest. But sometimes that just isn’t enough and my tolerance isn’t predictable.

I'm glad you brought this up because it's interesting to me that different people react differently to foods. I think some of this may be genetics, and maybe some of it is about the very individual -and very changeable - microbiome community we each have in our digestive systems.

Additionally, I wonder if there might also be ways to prepare foods that make them more gut-friendly. I wonder if part of why things like dosas and tempeh are part of traditional diets could have something to do with the fungi/bacteria/etc 'eating' some of the undigestible components? So that they are somewhat neutralized in the final product?

I was particularly curious about the saponins in beans and lentils, and when I did a quick internet search, this is one of the sites that came up:
https://healthygut.com/how-to-properly-prepare-beans/
Skimming through the page, I had heard about soaking beans in baking soda solution to make them cook up softer, but I'd never heard of soaking in an acid solution. In fact, a different site https://www.camelliabrand.com/soaking-salting-dried-beans-dos-donts-myths-more/
says,
"In terms of which ingredients you add and when, it is worth noting that acidic ingredients such as tomato sauce, wine, lemon juice or vinegar can prevent bean softening because acids act on the starch within bean cells, preventing them from swelling."
I have no idea if that would actually help. If you try it, I'd be curious to hear how it goes.

In terms of the lentil loaf specifically, I wonder if lentils would be more trouble-making --both because we don't usually pre-soak-and-rinse them, as many people usually do with other beans? And maybe the higher ratio of skins to meaty-insides could have something to do with it too?

. . . more tips from yet another webpage . . .
https://eatbeautiful.net/how-to-soak-beans-for-4-days-to-prevent-gas-which-beans-digest-best/
"Lastly, if you’re re-introducing beans"
"Do so slowly. Start with just 2 tablespoons to a quarter cup the first day, and increase gradually, so your body can get used to the increased fiber.
During digestion, the soluble fiber in beans clings to toxic bile. (Beans help to excrete toxins from the body!) But if eaten with fat, the fiber will cling to that instead. Do not add a lot of fat to your beans, and you will have less gas. When the fiber clings to the bile, less gas results. (This observation comes from Dr. Garrett Smith, who helps patients recover from vitamin A toxicity by implementing aspects of Karen Hurd’s Bean Protocol.)
Use a digestive aid: a splash of apple cider vinegar with your beans, digestive bitters with your meal or digestive enzymes that contain alpha-galactosidase."

Again, I haven't tried any of these myself, and you certainly can't believe everything you read!- but maybe something can give you some ideas about where to start.

A detailed description of some Indian cuisine, the same basic concept I outlined above, if your son and/or daughter-in-law want to be adventurous:
https://www.indianhealthyrecipes.com/handvo/

An little bit of info from wikipedia:
https://en.wikipedia.org/wiki/Dhokla

I soak my beans for 3 days in water, changing the water 3 times a day. Sugars which are hard to digest are removed during soaking, During the hot months of summer I add a little ice to the soak water during the day and refrigerate the pot of soaking beans overnight.
In addition I take the Walmart generic brand for Beano, it does not have mannitol in it which is an artificial sweetener that can cause digestive upset. I think Target also has a mannitol free form of Beano.
Another way to make beans more digestible is to sprout them. You can find on-line sources for how to do this. I tried garbanzo beans and it worked quite well, lentils are also suppose to be easy.

Thanks for the info re the Beano alternatives, I will try them. I assume when you say you are soaking beans, you mean dry ones, correct? For convenience my daughter-in-law typically uses canned beans when she cooks except for lentils. I’ve never heard of pre-soaking lentils but now I’m also hearing that canned lentils are digested more easily?

Yes, I soak dried beans and then pressure cook them. Pressure cooking breaks down sugars in beans, I forgot to include that in my explanation. I have read that canned beans are easier to digest also and assume the cooking process is similar to that of a pressure cooker. Avoid black beans for awhile, I find they are harder to digest which makes sense as they taste sweeter to me.
When using canned beans you might want to rinse them in water to remove the sugars that leached out of the beans during processing.
I have not tried canned lentils but should give them a try.