Changes in cat eating and defecation patterns

I am the owner of an almost 4 yr old female indoor cat that I adopted nearly a year ago. Up until now, she has been very healthy and her eating and urination/defecation patterns appeared normal. For the past three weeks (give or take a few days), she has been insatiably hungry, eating her food very quickly, and within minutes going to her litter box to (usually) defecate. Additionally her energy level has increased significantly and her behaviors seem out of character, as she is normally a reserved lap cat. No lethargy or weight loss has been noticed. In fact, despite her insatiability, no weight gain has been noted either.
   
Any ideas of what might be causing this?
   
Thank you!

It could be an overactive thyroid gland. Wolfing food is a red flag for this. This can be easily treated by a daily pill.
   
It could also be diabetes. This can be treated with insulin.
   
I've had both a hyperthyroid cat & a diabetic cat.
   
Go to the vet & have a full panel of blood tests done on the cat. Whatever the problem is will likely show up in the tests. They cost about $200 (Wash. D.C. area prices, maybe less in less expensive areas) & are worth every penny.