I have to be honest. I don’t think much of most nutrition advice from dieticians. In my case, after I was diagnosed I had conflict with my wife. I could not tolerate the amount of carbs in her cooking. Over that first year after diagnosis I eventually took over cooking and even shopping. My wife would still have tantrums at some meals asking “where are my carbs!” Over time we have worked through the issues. I learned to offer carbilicious selections for those in my family that want and could eat them. And over the years my wife has adopted low carb eating and lost weight.
I dramatically up my calories by eating lots of fat. For instance, if you have fish, then top it with this sauce which can add a add another 500-1000 calories per serving. I know you are saying that you are having digestion problems with fat. It may be that you have had some sort of gut isses. I might suggest trying to use probiotics and fermented foods to see if you can get your gut working better. You can get some basic probiotics in the vitamin aisle at the grocery store. I also eat all kinds of fermented foods like sauerkraut, pickles and yogurt. Another thing to do is up your fiber. On really good source of fiber is a type of noodle called shirataki (search the forum for this term). Shirataki has no carbs and is basically all fiber. It can be substituted for noodles, it makes a passable replacement for spaghetti noodles and really shines in pan fried noodles or in noodle soups.
Just some thoughts.