If you're looking to cut carbs...a diet program that nutrionists hate, but has been proven to be both effective AND healthy in multiple studies...you want to get rid of both rice and potatoes.
The best carbs are the ones with high fiber counts. Pretty basically, anything you want to feed him, read the label. It will give total carbs and fiber. Subtract fiber from total carbs, and that difference is the portion that turns to sugar. The higher the fiber amount as compared to the difference, the better. Both rice and potatoes have very poor ratios.
Another thing to consider is the glycemic index of the food. Along with the fiber/goes-to-sugar count, some foods turn to sugar far more slowly. My hubby was very pleased to find out that cake with a LOT of chocolate does not turn to sugar well at all. In fact, when he was watching his blood sugar carefully, we found that he could eat a very generous portion of chocolate cake with chocolate frosting without seeing any large rise in blood sugar.
My suggestion...as a wife that struggles with serving food that my husband likes and is not too unhealthy for him...is to carefully study both food labels and a glycemic index table, and see if you can gradually change the food in your house to higher fiber and lower glycemic index...without making your husband decided to drive to the closest store to load up on Twinkies.
Good Luck!!!