That’s the kind of question I expect from people who have recently changed to a new “protocol” -exercise, diet and behavior and aren’t sure what to do. Never be afraid to ask questions, to question the answers, because no one knows everything about anything.
What to do with fiber depends on whether you are a termite, a cow or a human, so you are better off asking this of a vet than an “medical doctor” or a “nutritionist”.
Unless you consider wood chips and hay as food, you should subtract dietary all fiber from your carb counts. Fiber is either soluble or insoluble in the human gut, but it is always indigestible.
If anybody tells you otherwise, they believe; they do not know.
They do not understand digestion or how to interpret the nonsense on food labels. Fiber is only under carbohydrates because it is not lipid or protein. Fiber should be shown as an inactive ingredient, as is done for medicine and supplements.
If fiber is listed as included under “Total carbs”, subtract all if it. It has no nutritional value for humans.
I don’t care what philosophy a doctor or nutritionist believes in. Those are “medical opinions”, not facts, but based on anecdotes and faith, like a religion.
I make decisions that effect my health based on facts and knowledge. As a human with type 1, if I didn’t subtract fiber from net carbs,no matter what I used as a insulin to carb ratio, I might as well be guessing.
btw, If you don’t look at added sugars as a percentage of the carbs in a meal, the response you get during the first two hours after you eat will be a surprise. If you don’t include enough or include too little fiber, your bathroom visits will too.
If you work to keep your diabetes well managed long enough you will find ways to simplify decisions because its too much work otherwise. You will eat more predictable meals of predictable sizes that include what you like to eat and nothing you don’t. You will condition your gut to expect certain size meals at certain times. That "diet will gradually change and you will become skilled at finding substitutes, one change at a time. You will look at new food and compare them to ones you know. Estimating food content will either become instinctive, or you will have a short list that you can refer to, not an encyclopedia of foods.
I have 4 breakfasts, 4 lunches and 6 dinner that I eat +45 weeks a year. My food diary has meal numbers, each meal has approximately 40 net carbs. I can substitute an ingredient for one of the fixed ones ad have a pretty close estimate of the effect,
If you are forced to eat food whose composition is unknown to you, the best you can do is compare it to things you know and compensate afterwards. When I eat out on vacation I mostly order things I know, with the variations being in fat and protein.