Get Lexi on a good probiotic & digestive enzyme. Bromelain in pineapple is what digests proteins, it's in digestive enzymes. Sometimes, pineapple doesn't work bc it only breaks down protein enzymes & doesn't help break down carbs from most kibbles. I would avoid foods heavy in potato or grains, that's what comes out the other end undigested & still smells like food to them.
HowStuffWorks "Bromelain: Enemy of Proteins Everywhere "