Hyperthyroidism?

Our two old cats are now constantly hungry.  We don't know if it is a case of no longer being able to supplement their diet with prey or more likely a common condition in older cats called Hyperthyroidism: but the amount they want to eat has quadrupled.

I suspected it 6 months ago and a blood test showed that one of them was borderline for this condition.  Their demands are getting worse and we are now living with constant miaowing for food - and Indie (the black one) is not a slim Jim.

Very tricky.