I have a question about food. When I look at the Pierson chart I find foods that she lists as low carb but when I put them into the carb calculator I find that although the food is low WET matter basis, it comes out much higher on a DRY matter basis. I usually try to find a food that comes out low on both accounts but does it matter? Is the WET matter basis what we go by because it is wet food?
carb calculator is here
https://www.caticles.com/carb-calculator-for-cat-food/
First, I would never use that calculator to calculate % calories from carbs. It uses guaranteed analysis (GA) which means there is a range of the macronutrients (fats, carbs, proteins).
Here is a long, but informative post I did on calculating % calories carbs. On
this page, under Q2, there is an Excel SS linked that is the best % calories from carbs calculator.
Second, there is no such thing as a wet food basis

There is an “as fed” or “as served” which includes moisture and I believe that’s what you must mean and a “dry matter basis”.
Third, the values on Dr. Lisa’s chart have already been converted to % calories from carbs so you can’t use those numbers to plug into a calculator.
The way dry food is formulated, it is made to be addictive to cats so that’s why it’s often difficult to transition them to a canned food. But it can be done (I’ve had to do it

). If you haven’t read
Dr. Lisa’s post on why NO dry food is best for cat’s, I’ve linked it so you can read it and she discusses how to transition a cat from dry to wet.
Here is another option for transitioning and the one I used for my cat.
The reason why the tight regulation (TR) protocol for Lantus/Levemir/Biosimilar users and the MPM don’t allow any dry food is that, even if the dry food is low carb, it takes longer to bring the BG up from low numbers and it stays in the system longer. Cats are obligate carnivores and in cats fed primarily a meat diet (canned or balanced raw), the carbs often come from carbs the meat when it was alive ate. Yes, there are some canned and raw foods which have blueberries, squash, etc added to them but these are not carbs that stay in the system long. For feeding our diabetic kitties, we want to find the canned or balanced raw LC food which best maintains their BG but, if the BG is low, can bring the BG back up quickly. Dry foods, even LC ones, don’t do this. Keep in mind that some cats, like my own Gracie, did better with wet foods that were in the 6% calories from carbs range. The tendency is to go straight for the 2% foods but that’s not always what best benefits a diabetic cat in working with insulin.
Having said all that, it’s more important for Opie to eat than whether you do MPM. That means if you have to start from scratch and give him the dry food he will eat while you are slowly transitioning him, then you’ll just need to do Start Low Go Slow until he’s eating wet food regularly. This takes time so be patient.
Please let me know if you have other questions.