I'm curious as to what sorts of viral, bacterial, or otherwise physiological sources could cause stomach discomfort in a vegetarian and in the presence of all of the following (in other words, having utilized): elimination diets, a low carb diet, intermittent fasting and grain elimination.
In vegans who have abdominal bloating/distension and excessive gas but otherwise feel healthy, the cause can be the ingestion of too much:
- Soluble fiber from legumes, oats, barley, rye, figs, prunes, artichokes, sweet potatoes, passion fruit, avocadoes (more foods)
(They are other vegan sources of protein, apart from legumes, such as bread, amaranth, cornmeal, kamut, quinoa, nuts, seeds (especially hemp) and hummus, that have less soluble fiber, so they should cause less gas.)
- Foods with high fructose/glucose ratio: apples, pears, mangoes, agave, watermelons, honey and foods and beverages sweetened by high fructose corn syrup (in case of fructose malabsorption) (UWHealth, more foods with high F/G ratio)
There can be certain foods that may irritate you from no apparent reason.
Vegans are often not aware of iron deficiency, but this tends to be common and can cause gastrointestinal symptoms.
To check for celiac disease, one could start a complete gluten-free diet after which the symptoms can improve in few weeks.
If nothing of the above helps, the next step can be to check for eventual food allergies (blood and skin tests), intestinal parasites (stool test), etc.