Why do some soy products give me a nasty stomach ache when other products are fine?

[NewYearSameMe]

The back story is that I ran out of krill oil supplements and bought a pack that is not my usual brand. I started taking them at bedtime on Tuesday and have woken up with stomach pain every night since. This morning I woke up and remembered that the pain was similar to the pain I had when I tried soya milk (I'm lactose intolerant so don't drink cows' milk). I checked the pack and it had soy lecithin and soy isoflavones so it probably is the cause. I can eat tofu and edamame with no problem at all so I don't understand why other soy products affect me so badly. Is it something to do with how they are processed?

Fermented vs non-fermented products?

I can't really find a difference that makes sense. Tofu, soy sauce, soy flour (small amount added to a lot of bread) and edamame (steamed beans in the pod) are all fine, so some fermented things and some not. Soy milk and now extracts in supplements cause pain within a few hours and I can't really see the difference. Especially between soy flour and soy milk which I think is just ground up dried beans with added water and then filtered.

Carrageenan? I'm intolerant to some plant milks that have it in. Took me ages to work out what it was that was upsetting me.

There wasn't any carageen in the krill oil supplement so I don't think it's that. I've bought some of my regular brand now and it only contains krill oil and fish oil, whereas the brand I tried last week had about 20 ingredients.

Anyway, all is well again in my digestive system. I could feel the discomfort working its way down and getting milder as it went, and now there's no pain at all. So at least it's just a temporary discomfort and no lasting damage.

Google FODMAP, the original Australian website, probably explains the whole lactose, soya thing. Not all of the dietary advice will apply to you but it might give you some guidance.

Thanks Zadoc, I'll have a look at that.