Please clarify one thing - does he have
diverticulitis, which is infection in the pockets in his bowels or
diverticulosis which are just the pockets in his bowels, uninfected. The two are treated entirely different and would make a world of difference in his care plan and his blood sugar control via his diet.
I am going to go with diverticulosis as otherwise he would not have been sent home without followup and allowed fiber and would be on antibiotics.
Your uncle's BMI is 18 indicating he is
underweight and malnourished and should have been referred to a dietitian for management of his weight, his diet, his blood sugar(you didn't say how high was high). It also sounds like he may be protein deficient with multiple nutrient deficiencies and an unbalanced fiber intake which would need to be balanced between water soluble/insoluble very slowly along with increased hydration and included into total allowable daily carbohydrates. And, where is his protein? His body ate his muscles up!!!! By the way, the flax muffins are treating his diverticulosis, so you can sort of give him a break there.
I am going to refer you to a dietitian to try to help him get on a reasonable nutritional plan that will gradually increase his calories and protein/nutrients according to his needs. You may find a dietitian near you by searching for The Academy of Nutrition and Dietitian. They have a tab that says "Find a Dietitian Near You", Click on that and enter your zip code. Hopefully someone in your area will pop up. If that doesn't work, there is a State Board of Dietetics in every State and Texas should have one also. They may be able to find someone to assist or even come to the home.
I don't see meat, cheese, milk or milk products, cheese, cottage cheese, fruits, vegetables, all these foods are missing from what you tell me he is eating. He is still grieving as well I am sensing. Has he ever seen a grief counselor? Do you think he would go or that it would help him? Eating problems are very often tied in with emotional holes in our lives.
Think about it. It is great he has someone like you to care and worry about him. He deserves quality of life too. My best wishes . . .Kathryn Shattler, MS,RDN