I have a cat that is 15 years old and was diagnosed with diabetes on April 20th. He had his fructosamine levels checked on May 20th and they said they were looking really good and almost in the range that they want him in (which was surprising for being on a 1 unit twice day dosage). My vet initially told me to stop his free feeding diet and switch to feeding him twice a day and that is what I have been doing for the past month+. My only concern is that he is very very skinny (his spine is easily felt and the area around his hips looks almost emaciated). Can I feed him more throughout the day to help him gain weight back or will that affect his glucose levels too much? I am not concerned with him not eating at injection time because any time he sees food he will be willing to eat.
I have a kitty who was in the same situation, age, weight, diagnosis, hungry reaching for the counter.....
Our vet also started with low insulin. But you need to get Kitty's weight up. Doc said liver will shut down without getting weight up.
So, we increased dosage of insulin. First to 2 units morning and another 2 at dinner. But it wasn't enough. Now he's on 4 breakfast, 3 dinner. Keep whip cream around in case giving too much insulin, to place on Kitty's gums is what vet told us, IF kitty passes out from too much insulin. That hasn't happened to us, Thank God - and it's an excuse for me to keep whip cream around. Lol
Also, I keep food out all the time. Crunchy, whatever favorites, treats. With very low weight, give some rotisserie chicken to my kitty. Yes, we know seasoning can be bad. But 15 years old and a boney spine is worse. Get the kitty eating. My kitty is fortunately NOT lactose intolerant, so milk helped put on some weight, but must be occasional treat.
Feed kitty all day round, but give them them yummy wet food for breakfast and dinner insulin times.
I'm not a vet, but spent a fortune on pates, all kinds to see what would stimulate kitty'appetite. Now, meals are a big deal. An hour long process. I found that after tossing blue buffalo burst treats into pate watered down to a thick bisque gravy, he would lap at it, because he's been spoiled by milk and rotisserie chicken. But with crunchy food out all day now, he nibbles while I'm at work, so not all his diet is yummy people food like rotisserie chicken.
15 is old. You have done a great job. Increase dosage, monitor and feed kitty everything and anything.
Btw, slowly increase dosage. If on 1 breakfast 1 dinner, start by going to 2 breakfast and 1 dinner.
Then 2 b-fast 2 dinner.
My kitty was a 14 pound kitten down to 7 pounds. Eating but not gaining weight. Always hungry. Insulin helped but not until dosage was increased. Vet will charge each time to tell you to slightly increase and monitor.
My 14 pound, now 7 pound increased slowly but is now at 4 units for breakfast, 3 units for dinner, fussing through the kitty pate bisque I make, knowing I have rotisserie chicken backup. It's not the best solution, but he's at 14 pounds again. Sad eyes when I tell him no milk. I even picked up whole milk because they say it's better than low-fat as kitties really shouldn't have any. But he needed to gain weight.
Delectables Stew treats for 15+ years, and Bisque for 10+ years is now also an every meal regular. I add water which helps keep them hydrated and wash out the foil pouch - if any hidden gravy is inside. They're a little over a buck but was less expensive than keep returning to the vet.
In summary:
Increased dosage, slowly.
Kept crunchy food out always.
Spoil the kitty at 15 years, anything kitty wants - get kitty eating.
Best of luck. Prayers with you and yours. Godspeed.

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I have attached a picture of how he looks now. (He was trying to see if we had any food for him on the counter, my poor baby)
View attachment 53819