Mikeey, if sugar bothers your pouch, you should know that dried fruits are highly concentrated in sugar. I suppose if prunes help you have formed BMs, you could slice one or two into your oatmeal for the fiber and sweetness. Food replacement drinks such as Ensure are high in carbs. Read the label before buying it. If something has more than 5 grams of carbohydrates per serving, that is a lot of sugar in one helping.
Mushrooms, asparagus are different in each person. You could buy the smallest quantity to cook and see how it affects you. If you love shrimp, try it and see. No one can know but you. One piece of advice my surgeon gave me was to introduce all foods to my new pouch, but to CHEW it thoroughly and carefully.
If you want to gain weight, try adding high fat, high protein foods such as peanut butter, almond butter, hazelnut butter, any nut butter is high fat and has protein. Avocado is high fat, and it's a good fat. I have it on toast, or in a sandwich in place of mayonnaise. Extra virgin olive oil is a good fat to drizzle on cooked vegetables, potatoes, into a bowl of soup, great for stir frying your shrimp! Eggs are high fat and protein. Cheddar cheese on toast or as a snack, same. Whole milk. Canned cream soups are high fat. Google high fat, protein food. Don't be afraid of food. Try small amounts.