Did your vet do any x-rays? I assume he/she did a complete urinalysis in addition to the bloodwork and that he checked for the more esoteric things like cat HIV...?
I had three cats last year who went into a sort of food aversion. They continued to drink water, so I didn't worry very much. One finally ejected very packed hairball sausages (she had been droopy for about 2 months), one had crystals in his bladder and couldn't urinate easily, so he gave up eating as well (he did, however, continue to drink). He is now on a maintance diet with low mangnesium. The last one we never did find out the reason. She went off one evening, came back four days later, and was thin again and had a much improved temper. The vet was simply unable to figure it out, and we did all the tests. Our next step was internal explorations, but fortunately she overheard us and took care of things herself! Smart kitty.
There are various things to help with poor eaters. There is a very nice liver paste you can give -- about half a teaspoon a day. You can explore liquid-type things ( maybe she would take some ground up chicken in a little good-old fashioned chicken soup...? My vet swears that it's the best thing for a sick cat -- or human! -- I have kept both sick dogs and sick cats hydrated with chicken soup, using a large syringe and frequent applications...)
And Sandie is right about depression. Both dogs and cats can become severely depressed, and, like people, they can sort of stop living after a point (anorexia is an example -- at some point, you turn a corner and simply don't want to eat anymore and your body refuses even intervenous feeding). So really be serious about the suggestion to check if something changed in the quality or durations of your interaction with the cat.
Once when I had a friend come to stay while she was visiting Israel, my cats -- almost all of them -- stopped eating, and only drank water outside in the yard. The house felt crowded to them, that was plain, but she didn't like cats in the room she slept in, and since I gave her mine (the only good bed in the place), the cats were barred from it day and night. In the daytime, they like to sleep on top of the thick horseblankets I put on it to protect it. They and the dogs sleep all over the bed during the day. At night, several of the dogs prefer to be under the TV table and the youngest cats want to sleep at the foot of the bed because they feel more secure. When my friend was here, they couldn't do these familiar things, and my whole pride and pack began to pine. Fortunately my friend went home after three weeks. The first day they could get back in, I had three dogs (at that time) and 14 cats all piled onto the bed (a small single) in a huge tangle of legs and bodies. They repeated this rather frantic behavior for almost two weeks after she went, and kept coming into the house to check that she was really gone.
I learned from all this that cats in particular, but even the more adaptable dogs, can really become insecure and nervy when their special territories are invaded by outside influences. Next visit, I will get my friend a camp cot for the computer room (which the animals don't come in unless I am working there), and I will maintain the sanctity of the bedroom for the mental health of my "family."