Here’s where they are totally right and totally wrong at the same time. From the Mayo Clinic site (Avoid weight gain while taking insulin).
Take your insulin only as directed. Don’t skip or reduce your insulin dosages to ward off weight gain. Although you might shed pounds if you take less insulin than prescribed, the risks are serious. Without enough insulin, your blood sugar level will rise — and so will your risk of diabetes complications.
I get what they are saying. If you need insulin to regulate your blood sugar and you go off it then you’ve got serious problems up to death. The thing a diabetic should be watching isn’t the amount you were prescribed. It should be the amount needed to regulate your blood sugar. No more.
My doctor started me out by telling me that I needed to take 40 units of long-lasting insulin. When that led to a high HbA1C number he said that I needed to add meal-time insulin. I wish they would not call it that. So many false things there. He told me to use the 2nd Insulin and use 8 units before every meal. The diabetic nurse told me that was wrong and she had him fix the prescription.
They got me nutritional training and told me to count carbs. Not count as in limit, but to bolus for the amount of grams of carbs in what I was eating. Good advice for high carb meals. Not great when you consider gluconeogenesis. That all got me to a decent point of glucose control but was about 60 units a day (40 of basal and 20 of “meal-time” (fast acting) Insulin. In the last 5 years I have progressed to around 100 units a day (varies by my carb intake). It’s only now that I am getting lower than when I was diagnosed.
I am using less by doing LCHF (really mostly LC) and Intermittent Fasting (IF). Yesterday I used a total of 47 units of Insulin. I will lower my basal (constant) Insulin rate tomorrow to drive my Insulin levels even lower.