The killer gratin: sweet potato, eggplant, and gorgonzola As I mentioned, sweet potato has a glycemic index of 50, which is relatively low compared to regular potatoes, especially when combined with the fiber from the eggplant and the fat from the cheese, which will lower the overall glycemic index of the recipe. We also added a slice of ham to go with it. It was delicious, my taste buds still remember it.