| Sandpaper = non-white. Bran, whole wheat, multi-grain, etc. White flour is about as bad as sugar. Whole grains are digested much more slowly and don't spike our sugars. When mixed with these, proteins, and fats, fast acting foods are absorbed more slowly too.
He does need fat. It is a vital part of our diets. He does not need a lot. Others hare can and will recommend types, but it's more a long term thing.
Salt isn't needed. We eat too much of it. Again, it's a long term thing affecting our cardiovascular systems.
I don't think a short term lack of salt or fat would cause his symptoms. He needs food (energy). Without insulin we starve despite filling ourselves with food. Insulin is what lets our cells use it. He very likely does need insulin to feel better, oth for energy and for getting his BGs down, but that's up to the doctors to determine. His metformin may still be enough. | 
