for my female lab when she became ill (from contaminated dog food) and lost all kinds of weight I quickly fattened her up by going all natural, boneless chicken (because she hates beef) or ground pork, brown rice, potatoes, 1 tomato, carrots and celery. I browned the meat and then I added everything into a pot added some water and made a thick stew, I sometimes would add 1/2 cup lentils , to avoid her only eating the meat I would break it down with a stick blender a little bit. I would make enough for a few days and once she was able to go back on dog food I kept on adding 1/2 cup to her dry food. the natural diet bounced her right back and within 2 weeks I had to take her off because she got too thick. I now only buy all natural dry dog food its expensive and its delivered from a mill in Toronto to the local feed store here in my town. she eventually lost the extra few pounds and she is in optimal health now. If I see one of my dogs is getting thin, usually happens in spring... I make the stew and add a bit to their dry food, works every time!!