I'm not sure but I think even poverty-stricken people in many parts of Asia will only eat white rice. If they received brown rice they might not even eat it! In other parts of Asia they eat red rice or black rice which is a different whole rice variety, so it just depends on the place.
Anyway if you combine the GABA rice for poverty with the warrior diet idea, they can eat their main meal in the evening of GABA rice and then it won't matter if they are sleepy. Whether or not they eat in the day won't matter too much, and they can eat any other items they may have available or find.