texaszet

My cat has been gradually losing weight for two months for no reason. She had a complete check-up at the vet on Monday (full physical exam, blood work, and fecal), but everything came back completely normal. Nothing was even on the cusp of being abnormal. Since my cat is a purebred Maine Coon (they grow for 3-5 years) and only 19 months, my vet recommended putting her back on kitten food to increase her caloric and protein intake. She acts totally normal (as in runs laps around my apartment for a few hours every day), is very affectionate, and eats a lot, but she is just losing weight. Has anyone else experienced something like this?