This patient support community is for questions related to juvenile diabetes including celiac disease, depression, diabetic complications, hyperglycemia / diabetic keto-acidosis, hypoglycemia, islet cell transplantation, nutritional issues, parenting a diabetic child, pregnancy, pump therapy, school issues, and teens with diabetes.
It often takes hours for all our food to be digested, but carbohydrates are digested more quickly. Simple sugars are digested even more quickly & some are initially digested in our mouth. Fats & proteins take longer.
Depending on what we eat, we could get a blood sugar rise in just a few minutes or -- if it's complex carbohydrates mixed with proteins and fats, the rise will be more gradual and over a long period of time, as you mention.
I'm not a physician or nutritionist, but this is how I understand digestion to work. I try to take my insulin (dose & timing) based on what's in the food I'm eating.