Hunger strike

My 7 year old cat has stopped eating his food. I am feeding Origen. He has gotten very thin. His teeth and gums are fine. He has no worms. He is still active and playing. He just eats enough to survive but he is very hungry. He has even snatched food right out of my hands. This is something he has never done before. I tried another pet store food and he ate it for one day and wouldn't eat it again. I give him moist food once a week and do not feed him any table scraps. I have stopped feeding him his favorite treat "Temptations" in hopes that he will eat his food but he doesn't. Am I missing something?

Sounds like he's gone stubborn on you. He's bored with his food, he doesn't want it any more, & you aren't listening. The other brand you offered wasn't right, as far as he was concerned.
   
It's amazing how stubborn a cat can be.
   
There's no reason why you shouldn't change his food brand. Go to the local pet superstore & get some sample packs of Iams, Hills Science Diet, Royal Canin, Authority & NutroMax kibble, all perfectly good brands that I've fed my cats off & on for the last 30 years. Ask at the desk for sample packs, they usually have some on hand.
   
Also pick up one can of 3 or 4 of the above brands. Mix a quarter-can of wet to about three-fourths of his usual serving of dry kibble. This may interest him more.
   
I feed my cats dry in the morning, & the wet-dry mix above in the evening, & I change the canned brand/flavor every couple of days - I buy an assortment of brands & flavors & rotate them.
   
Dump the water from the tunafish can on his food whenever you open a can. Most cats love this.
   
To put some more weight on him, give him some kitten food mixed in with the standard adult food for a few weeks - more calories is good for a thin cat.