We have a dear friend who is both diabetic and has kidney disease, so also has to eat low-potassium. As I'm sure you know, most of the items on these diets are polar opposites...a diabetic is told to eat whole grains, yet a diabetic with kidney disease must eat only white breads, never whole grains. It's not easy, and the dietician is the way to go...check online for recipes and cookbooks that are geared for diabetics with kidney disease. We bought one for our friend, and it has home made sausage recipes, muffins, and all sorts of things that made meals interesting for her again. You can't be his mother, but you can be his helpmeet. Look for resources together online, try to find the challenge of coming up with the best tasting food that meets the criteria. Fresh herbs change the taste of simple salads, and by having small munchy sorts of things on hand that fit his diet, he'll be less likely to try someone else's food. Best of luck!