Both buckwheat and brown rice are rated medium on glycemic index, 54 and 55 respectively. I don't understand why buckwheat would be allowed on a diet and not b rice regardless of how the food is classified.
I had asked dr jeff that question some months ago when I was doing his diet. Ironically he allowed b rice but not bwheat. I was disappointed but went with his model.
In any event, I love buckwheat/kasha. I now eat it as breakfast cereal or with lunch. Also make a muffin type bread with it.