I Am 70 Yr Old And Weigh 270, I Was

I am 70 yr old and weigh 270, I was 300 until Dr. put me on water pills I went down to 250 in a few months. then I had aKidney removed & had to go to 1/2 of a water pill my weight is coming back up. I don't really eat that much my nutritionist says I need to eat more. I have kept a log of two years and average 1200- 1500 cal/day. I am Diabete type 2 and my A!C is between 6.5 & 7.0. My wife and I are together 24 hrs a day and she has sneak food when I am in the den to keep from loosing weight. We eat the same things and split meals if we eat out. We both have Polio and wear leg braces but we get in a mile walk a day I don't know what more to do.