All my cats are free feeders and one especially Misha is a big girl but we started to worry last year as she looked bigger than normal and started limping - we had her tested for everything and anything but internally all fine and no signs of arthritis, etc so vets put her in the fat club (even though I had said she wasn't a piggy cat - she hates anything bar her biscuits and hates soft food), anyways after many weigh ins and her weight fluctuating without any rhyme or reason the vet decided she has a somatic cat and some cats weight just does fluctuate madly!