@jerusa Purina Pro Plan is a good food line. With that said, the same diet doesn't work for every dog. Normally for an underweight dog I would recommend a higher fat diet, likely a 30/20 formula (30% protein, 20% fat). However, his digestive issues could indicate a problem digesting fat in the first place, so I always recommend double checking with your veterinarian if your pet has issues. Some 30/20 formulas include:
