Is your husband taking prescription strength enzymes at all? What works for me is to take them throughout a meal. One with first bite of meal, one in middle of meal and one toward the end of the meal. I take Creon, but there are other brands available as well.
If he isn't seeing his doctor already about the weight loss and vomiting, he should.
My experience is that the symptoms you mention, gas, bloating and abdominal pain should be helped and in some cases eliminated by taking enzymes in enough quantity. Dumping syndrome can happen if you eat things high in sugar content. Some of the protein drinks, like Ensure, can have lots of sugar. It is often trial and error until you find what foods affect you adversely. Keeping a food diary helped me. Also, for some folks it helps to drink liquids after the meal, or between meals instead of during meals. Weight loss can be caused by malabsorption of food, and in my case, getting the enzymes started and learning to how to take them stopped the weight loss.
Hope your husband's situation improves soon.