... not tried soya/tofu yet but it was one of my faves especially in miso.
Then perhaps don't startspecially bearing in mind your stomach problems. Miso's different: it's fermented, which renders it more digestible. Contrary to industry propagandawe're talking absurdly wealthy agribusiness herepeople in Asia don't eat
that much soy and traditionally tend to
ferment it. This is because of the "antinutrients" it contains. Google this for more information:
soy antinutrients
Also, did you know Buddhist monks used to eat it to
curb their sexual urges? It contains phyto-oestrogensplant componuds that resemble
female sex-hormone. Does that sounds like a good deal? Google:
soy phytoestrogens
(U.S. spelling will get you more links.)
Same antinutrient deal goes for all pulses (although soy is the worst). Traditionally, these foodstuffs were soaked for hours, lactic-fermented, and/or boiled for extended periods. That wasn't for nothing. Similar issues exist with cereal grains.
If you've got trouble with your stomach it's likely your gut flora is disturbed. Antibiotic use, and a few other things, can do that. It's a helluva problemand not just for humans:
Cellular and humoral immunodepression in vultures feeding upon medicated livestock carrion
http://rspb.royalsocietypublishing.org/content/276/1665/2307.full.pdf
I'd definitely seek medical advice, but in the meantime a good quality probiotic can't do any harm and will likely do some good. Lactic-fermented foods such as yoghurt and (real) sauerkraut can also help.
Prebiotics might do, too:
http://en.wikipedia.org/wiki/Prebiotic_(nutrition)
Gelatinous stocks and soups are also good. They're soothing to the stomach and help you to digest the flesh-foods you mention. Nowadays, people tend to eat too much muscle meat and miss the organ meats and the skin-and-bones (in broths or whatever). It's not a good thing.