EPI is Exocrine Pancreatic Insufficiency basically the pancrease stops functioning and enzymes are needed for life to help the body process the goodness in foods but I am a learner to all this but that seems the basis of it. There are many other things that also help along the way eg B12 shots weekly diet antibiotics for the secondary condition of EPI which is SIBO the story goes on and on and the bills and products. Basically its a long hall of trial and era it seems but they tell me once the condition is stable which could take months the dogs can return to a healthy weight and lifestyle. This is a link I have found helpfull on my journey http://www.epi4dogs.com/