My oldest gal, London, is about 12. She has always been thin, even when I first got her at about 2 years of age as a rescue, but over the past few months, she has lost even more weight. Vets all say she is fine, nothing wrong with her, just a fast metabolism and a high activity level. But I'd really like for her to put on some weight at this point. I know it's got to be cold going outside to go to the bathroom when she is so thin and has no insulation. I'm trying to think of things that I could add to her food to give her a good source of fat. I was thinking eggs? I also thought of canned fish, but isn't fish pretty lean? Any other ideas? Increasing food, trying many different foods, etc. have never made very much of a difference in her weight. She is a picky eater and sometimes eats like a bird.