So, fewer carbs = less glucose in your system, which means your body will have to start burning fat as your fuel source. (nerdfitness.com)
Because glucose has been moved to your fat cells, there is less circulating glucose and therefore less glucose available to your brain. (rachaelattard.com)
Because there fit is poor, the door does not open fully and therefore less glucose comes in than normal. (idmprogram.com)