When we first had Gypsy, she was awfully skinny and didn’t help herself by refusing food.  After several visits to the vets, we found that she was intolerant to many foods and so was probably not eating as she constantly felt poorly.  Thankfully we discovered Nature’s Menu http://www.naturesmenu.co.uk whose food she loves (especially the chicken and salmon combo!) so she soon reach a healthy weight, ready to go out and explore the world.