cats having a pro absorbing protiens

my domestic short hair approx 7 yrs old has a problem absorbing or losing protien through here intestins. which has made here very thin(kind of sickly looking)and has little muscle mass. she's been to the vets, had blood work done and the result is that she losing the protiensbut is maintaining weight and maybe gained a pound. Im feeding here dry, canned, and real beef and chicken all the time. with not much results. does anyone have some ideas i can try/ help her put some much need weight back on?

YOu need to find out WHY... I suggest asking the vet if there is a feline specialist in your area ....

What tests have been run??