Insulin users - do you use total carbs, or adjust based on fiber/sugar alcohols?

My husband is a long time DM2 insulin user, and has frequently been having low BG recently.

For background info - I am currently eating a keto diet for fertility purposes, but this has meant he is eating more fiber via vegetables, sugar alternatives and bread alternatives. His doctor has told him not to subtract any of the fiber or sugar alcohol content, and I'm worried this is part of the reason.

He has not lost any weight either, he has actually gained a lot since COVID, so I don't think his insulin sensitivity has improved.

Hoping to hear some of your personal experiences!