Chestnut Flour

While chestnut flour is still considered a high glycemic index food (the
source I consulted rated it a ~65 on the index; a food must be 50-55 or
lower to be considered 'low'), it is still considerably lower on the GI
scale than typical flours used for baking, glutinous and gluten-free
alike, such as white rice flour (GI=~95), potato starch (GI=~95),
Arrowroot starch (GI=~85) and white (wheat) flour (GI=~85)**. To be
sure, it's considerably more expensive (and hard to find), but for those
of you looking for lower GI, GF substitutes for the white rice flour in
your recipes, chestnut flour could be a good option... so long as you're
not allergic to tree nuts, that is.

http://www.tamaraduker.com/2009/09/discovering-chestnut-flour/