I find that in my own case, the intrinsic variability of insulin needs is so extreme that the only way I can stabilize things adequately is to weigh all the food I eat and eat exactly the same food at exactly the same time every day. I would have to make a conscious decision to readjust these parameters if I wanted to gain weight, and I’ve never had any reason to want to do that, though once, on the first day of classes, a student in the front row in a course I was giving whispered to her friend, “He’s so skinny he looks sick!”
I also weigh myself regularly, since that is a good way to check for diabetic renal disease without bothering with a creatinine test, since fluid weight gain is a sign the kidneys are not processing urine as they should. But the only way to make this weighing informative is to eat the same thing all the time so as not to gain non-fluid weight.
The only variable is the amount I have to eat to correct lows, and that does induce some variation, but I have more or less worked that into the daily caloric intake allowed.
These habits come from the way diabetes was treated when I was first diagnosed in 1966, and I was put on an assigned ration of calories of carbohydrate, protein, and fat, and never allowed to stray from it. I was starving all the time and dreamed every night of nothing but food, since the diet was way below the normal consumption of an ordinary teenage male. I suspect that the Joslin’s Clinic, which kept me on that cruel diet, might have been secretly trying to give me some compensatory longevity advantage, since experiments with mice in the 1950s had shown that if they were placed on a starvation diet when young, they lived longer. It may also have been because old ideas die hard, and since it was necessary to starve diabetic children in the pre-insulin era, and that time was only 40 years after it, somehow they still felt starving diabetic children was a necessary treatment.