My son never had stomach problems. However, for the most part, he has always preferred 'plainer' foods. Although he likes spicy foods, he's never liked foods with lots of ingredients or toppings, i.e. plain meat and potatoes type of meals rather than stews, stirfries, etc.
An interesting side note, my daughter has always eaten and liked almost everything (as exotic as you can imagine! LOL), but had a distaste for some very common things that surprised me (i.e., melons, corn). It turned out that she has slight sensitivies/allergies to these foods. Her allergist suggested that, even as a young child, she may not have felt 'well' after eating these foods and instinctively avoided them.
Makes me wonder if that same instinctive mechanism is what developed my son's preferences for 'plainer' foods??? Perhaps, there were foods that bothered his stomach that he just avoided???
Just a thought...