Bulk ingredient for keto/low carb flour substitute mix with gluten
Konjac flour, which consists mainly glucomannan gum, is a natural low-carb bulking ingredient. I have never used it in baking, but I ate noodles made of it. It does have its taste though, so you should probably try eating some shirataki noodles before ordering and baking with this flour to know if you can tolerate the taste.