skinny but eats alot!

she has lost alot of weight (half over a couple of years), had blood tests done, could becoming diabetic. 2 yrs later, no signs of diabetes, still eats a tremendous amount yet not gaining any weight. No sign of worms. Bathroom habits are normal. Water intake normal. Question is in regards to her appetite, she eats so much. Yet she`s not terribly active being a senior. Live in the country with access outdoors.

Have her checked for an overactive thyroid. This causes cats to eat a lot yet still lose weight. It revs the system into overdrive.
   
If that's it, it's easy to treat: a daily pill to quiet the thyroid gland takes care of it. I had a cat with this problem, he was fine after he got his pills.