Brown rice flour (aka BRF), the product of powdering brown rice, is a popular substrate for growing mushrooms. Its use as a substrate was made popular by the use of cake spawns in the PF Tek method of growing. It is most often powdered into a flour and combined with vermiculite.
Comparison to white rice
Brown rice and white rice have similar amounts of calories, carbohydrates, fat and protein. Many types of brown rice however contain far more fat than white rice. Reports suggest that the use of white rice in growing mushrooms results in differing chemistry within the mushroom and dramatically lessened potency of magic mushrooms. See the shroomery white rice grow log for details on limited potency.